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<span class="navbar-brand">Gtk4 tutorial</span>
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<a class="nav-link" href="sec30.html">Prev: section30</a>
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<a class="nav-link" href="sec32.html">Next: section32</a>
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<div class="col-xl-10 col-xxl-9">
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<h1 id="gtkexpression">GtkExpression</h1>
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<p>GtkExpression is a fundamental type. It is not a descendant of
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GObject. GtkExpression provides a way to describe references to values.
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GtkExpression needs to be evaluated to obtain a value.</p>
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<p>It is similar to arithmetic calculation.</p>
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<pre><code>1 + 2 = 3</code></pre>
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<p><code>1+2</code> is an expression. It shows the way how to calculate.
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<code>3</code> is the value comes from the expression. Evaluation is to
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calculate the expression and get the value.</p>
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<p>GtkExpression is a way to get a value. Evaluation is like a
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calculation. A value is got by evaluating the expression.</p>
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<h2 id="constant-expression">Constant expression</h2>
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<p>A constant expression (GtkConstantExpression) provides constant value
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or instance when it is evaluated.</p>
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<div class="sourceCode" id="cb2"><pre class="sourceCode c"><code class="sourceCode c"><span id="cb2-1"><a href="#cb2-1" aria-hidden="true" tabindex="-1"></a> GValue value <span class="op">=</span> G_VALUE_INIT<span class="op">;</span></span>
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<span id="cb2-2"><a href="#cb2-2" aria-hidden="true" tabindex="-1"></a> expression <span class="op">=</span> gtk_constant_expression_new <span class="op">(</span>G_TYPE_INT<span class="op">,</span><span class="dv">100</span><span class="op">);</span></span>
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<span id="cb2-3"><a href="#cb2-3" aria-hidden="true" tabindex="-1"></a> gtk_expression_evaluate <span class="op">(</span>expression<span class="op">,</span> NULL<span class="op">,</span> <span class="op">&</span>value<span class="op">);</span></span></code></pre></div>
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<ul>
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<li>GtkExpression uses GValue to hold a value. GValue is a structure and
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container to hold a type and value. It must be initialized with
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<code>G_VALUE_INIT</code>, first. Be careful that <code>value</code> is
|
||
a structure, not a pointer to a structure.</li>
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<li>Constant expression is created with
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<code>gtk_constant_expression_new</code> function. The parameter of the
|
||
function is a type (GType) and a value (or instance). This expression
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||
holds a constant value. <code>G_TYPE_INT</code> is a type that is
|
||
registered to the type system. It is integer type. Some types are shown
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in the following table.</li>
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<li><code>gtk_expression_evaluate</code> evaluates the expression. It
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has three parameters, the expression to evaluate, <code>this</code>
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instance and a pointer to a GValue for being set with the value.
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<code>this</code> instance isn’t necessary for constant expressions.
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Therefore, the second argument is NULL.
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<code>gtk_expression_evaluate</code> returns TRUE if it successfully
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evaluates the expression. Otherwise it returns FALSE.</li>
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<li>If it returns TRUE, the GValue <code>value</code> is set with the
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value of the expression. The type of the value is int.</li>
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</ul>
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<table>
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<thead>
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<tr class="header">
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<th style="text-align: left;">GType</th>
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<th style="text-align: left;">C type</th>
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<th style="text-align: left;">type name</th>
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<th style="text-align: left;">notes</th>
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</tr>
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</thead>
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<tbody>
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<tr class="odd">
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<td style="text-align: left;">G_TYPE_CHAR</td>
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<td style="text-align: left;">char</td>
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<td style="text-align: left;">gchar</td>
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<td style="text-align: left;"></td>
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</tr>
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<tr class="even">
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<td style="text-align: left;">G_TYPE_BOOLEAN</td>
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<td style="text-align: left;">int</td>
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<td style="text-align: left;">gboolean</td>
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<td style="text-align: left;"></td>
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</tr>
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<tr class="odd">
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<td style="text-align: left;">G_TYPE_INT</td>
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<td style="text-align: left;">int</td>
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<td style="text-align: left;">gint</td>
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<td style="text-align: left;"></td>
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</tr>
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<tr class="even">
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<td style="text-align: left;">G_TYPE_FLOAT</td>
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<td style="text-align: left;">float</td>
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<td style="text-align: left;">gfloat</td>
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<td style="text-align: left;"></td>
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</tr>
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<tr class="odd">
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<td style="text-align: left;">G_TYPE_DOUBLE</td>
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<td style="text-align: left;">double</td>
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<td style="text-align: left;">gdouble</td>
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<td style="text-align: left;"></td>
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</tr>
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<tr class="even">
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<td style="text-align: left;">G_TYPE_POINTER</td>
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<td style="text-align: left;">void *</td>
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<td style="text-align: left;">gpointer</td>
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||
<td style="text-align: left;">general pointer</td>
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||
</tr>
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<tr class="odd">
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<td style="text-align: left;">G_TYPE_STRING</td>
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||
<td style="text-align: left;">char *</td>
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||
<td style="text-align: left;">gchararray</td>
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||
<td style="text-align: left;">null-terminated Cstring</td>
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||
</tr>
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||
<tr class="even">
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||
<td style="text-align: left;">G_TYPE_OBJECT</td>
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<td style="text-align: left;"></td>
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||
<td style="text-align: left;">GObject</td>
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||
<td style="text-align: left;"></td>
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||
</tr>
|
||
<tr class="odd">
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||
<td style="text-align: left;">GTK_TYPE_WINDOW</td>
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||
<td style="text-align: left;"></td>
|
||
<td style="text-align: left;">GtkWindow</td>
|
||
<td style="text-align: left;"></td>
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||
</tr>
|
||
</tbody>
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||
</table>
|
||
<p>A sample program <code>exp_constant_simple.c</code> is in
|
||
<code>src/expression</code> directory.</p>
|
||
<div class="sourceCode" id="cb3"><pre
|
||
class="sourceCode numberSource C numberLines"><code class="sourceCode c"><span id="cb3-1"><a href="#cb3-1"></a><span class="pp">#include </span><span class="im"><gtk/gtk.h></span></span>
|
||
<span id="cb3-2"><a href="#cb3-2"></a></span>
|
||
<span id="cb3-3"><a href="#cb3-3"></a><span class="dt">int</span></span>
|
||
<span id="cb3-4"><a href="#cb3-4"></a>main <span class="op">(</span><span class="dt">int</span> argc<span class="op">,</span> <span class="dt">char</span> <span class="op">**</span>argv<span class="op">)</span> <span class="op">{</span></span>
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||
<span id="cb3-5"><a href="#cb3-5"></a> GtkExpression <span class="op">*</span>expression<span class="op">;</span></span>
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||
<span id="cb3-6"><a href="#cb3-6"></a> GValue value <span class="op">=</span> G_VALUE_INIT<span class="op">;</span></span>
|
||
<span id="cb3-7"><a href="#cb3-7"></a></span>
|
||
<span id="cb3-8"><a href="#cb3-8"></a> <span class="co">/* Create an expression */</span></span>
|
||
<span id="cb3-9"><a href="#cb3-9"></a> expression <span class="op">=</span> gtk_constant_expression_new <span class="op">(</span>G_TYPE_INT<span class="op">,</span><span class="dv">100</span><span class="op">);</span></span>
|
||
<span id="cb3-10"><a href="#cb3-10"></a> <span class="co">/* Evaluate the expression */</span></span>
|
||
<span id="cb3-11"><a href="#cb3-11"></a> <span class="cf">if</span> <span class="op">(</span>gtk_expression_evaluate <span class="op">(</span>expression<span class="op">,</span> NULL<span class="op">,</span> <span class="op">&</span>value<span class="op">))</span></span>
|
||
<span id="cb3-12"><a href="#cb3-12"></a> g_print <span class="op">(</span><span class="st">"The value is %d.</span><span class="sc">\n</span><span class="st">"</span><span class="op">,</span> g_value_get_int <span class="op">(&</span>value<span class="op">));</span></span>
|
||
<span id="cb3-13"><a href="#cb3-13"></a> <span class="cf">else</span></span>
|
||
<span id="cb3-14"><a href="#cb3-14"></a> g_print <span class="op">(</span><span class="st">"The constant expression wasn't evaluated correctly.</span><span class="sc">\n</span><span class="st">"</span><span class="op">);</span></span>
|
||
<span id="cb3-15"><a href="#cb3-15"></a> gtk_expression_unref <span class="op">(</span>expression<span class="op">);</span></span>
|
||
<span id="cb3-16"><a href="#cb3-16"></a> g_value_unset <span class="op">(&</span>value<span class="op">);</span></span>
|
||
<span id="cb3-17"><a href="#cb3-17"></a></span>
|
||
<span id="cb3-18"><a href="#cb3-18"></a> <span class="cf">return</span> <span class="dv">0</span><span class="op">;</span></span>
|
||
<span id="cb3-19"><a href="#cb3-19"></a><span class="op">}</span></span></code></pre></div>
|
||
<ul>
|
||
<li>9: A constant expression is created. It holds an int value 100. The
|
||
variable <code>expression</code> points the expression.</li>
|
||
<li>11-14: Evaluates the expression. If it successes, show the value to
|
||
the stdout. Otherwise show an error message.</li>
|
||
<li>15-16: Releases the expression and unsets the GValue.</li>
|
||
</ul>
|
||
<p>Constant expression is usually used to give a constant value or
|
||
instance to another expression.</p>
|
||
<h2 id="property-expression">Property expression</h2>
|
||
<p>A property expression (GtkPropertyExpression) looks up a property in
|
||
a GObject instance. For example, a property expression that refers
|
||
“label” property in a GtkLabel object is created like this.</p>
|
||
<div class="sourceCode" id="cb4"><pre class="sourceCode C"><code class="sourceCode c"><span id="cb4-1"><a href="#cb4-1" aria-hidden="true" tabindex="-1"></a>expression <span class="op">=</span> gtk_property_expression_new <span class="op">(</span>GTK_TYPE_LABEL<span class="op">,</span> another_expression<span class="op">,</span> <span class="st">"label"</span><span class="op">);</span></span></code></pre></div>
|
||
<p>The second parameter <code>another_expression</code> is one of:</p>
|
||
<ul>
|
||
<li>An expression that gives a GtkLabel instance when it is
|
||
evaluated.</li>
|
||
<li>NULL. When NULL is given, a GtkLabel instance will be given when it
|
||
is evaluated. The instance is called <code>this</code> object.</li>
|
||
</ul>
|
||
<p>For example,</p>
|
||
<div class="sourceCode" id="cb5"><pre class="sourceCode C"><code class="sourceCode c"><span id="cb5-1"><a href="#cb5-1" aria-hidden="true" tabindex="-1"></a>label <span class="op">=</span> gtk_label_new <span class="op">(</span><span class="st">"Hello"</span><span class="op">);</span></span>
|
||
<span id="cb5-2"><a href="#cb5-2" aria-hidden="true" tabindex="-1"></a>another_expression <span class="op">=</span> gtk_constant_expression_new <span class="op">(</span>GTK_TYPE_LABEL<span class="op">,</span> label<span class="op">);</span></span>
|
||
<span id="cb5-3"><a href="#cb5-3" aria-hidden="true" tabindex="-1"></a>expression <span class="op">=</span> gtk_property_expression_new <span class="op">(</span>GTK_TYPE_LABEL<span class="op">,</span> another_expression<span class="op">,</span> <span class="st">"label"</span><span class="op">);</span></span></code></pre></div>
|
||
<p>If <code>expression</code> is evaluated, the second parameter
|
||
<code>another_expression</code> is evaluated in advance. The value of
|
||
<code>another_expression</code> is the <code>label</code> (GtkLabel
|
||
instance). Then, <code>expression</code> looks up “label” property of
|
||
the label and the evaluation results in “Hello”.</p>
|
||
<p>In the example above, the second argument of
|
||
<code>gtk_property_expression_new</code> is another expression. But the
|
||
second argument can be NULL. If it is NULL, <code>this</code> instance
|
||
is used instead. <code>this</code> is given by
|
||
<code>gtk_expression_evaluate</code> function.</p>
|
||
<p>There’s a simple program <code>exp_property_simple.c</code> in
|
||
<code>src/expression</code> directory.</p>
|
||
<div class="sourceCode" id="cb6"><pre
|
||
class="sourceCode numberSource C numberLines"><code class="sourceCode c"><span id="cb6-1"><a href="#cb6-1"></a><span class="pp">#include </span><span class="im"><gtk/gtk.h></span></span>
|
||
<span id="cb6-2"><a href="#cb6-2"></a></span>
|
||
<span id="cb6-3"><a href="#cb6-3"></a><span class="dt">int</span></span>
|
||
<span id="cb6-4"><a href="#cb6-4"></a>main <span class="op">(</span><span class="dt">int</span> argc<span class="op">,</span> <span class="dt">char</span> <span class="op">**</span>argv<span class="op">)</span> <span class="op">{</span></span>
|
||
<span id="cb6-5"><a href="#cb6-5"></a> GtkWidget <span class="op">*</span>label<span class="op">;</span></span>
|
||
<span id="cb6-6"><a href="#cb6-6"></a> GtkExpression <span class="op">*</span>expression<span class="op">;</span></span>
|
||
<span id="cb6-7"><a href="#cb6-7"></a> GValue value <span class="op">=</span> G_VALUE_INIT<span class="op">;</span></span>
|
||
<span id="cb6-8"><a href="#cb6-8"></a></span>
|
||
<span id="cb6-9"><a href="#cb6-9"></a> gtk_init <span class="op">();</span></span>
|
||
<span id="cb6-10"><a href="#cb6-10"></a> label <span class="op">=</span> gtk_label_new <span class="op">(</span><span class="st">"Hello world."</span><span class="op">);</span></span>
|
||
<span id="cb6-11"><a href="#cb6-11"></a> <span class="co">/* Create an expression */</span></span>
|
||
<span id="cb6-12"><a href="#cb6-12"></a> expression <span class="op">=</span> gtk_property_expression_new <span class="op">(</span>GTK_TYPE_LABEL<span class="op">,</span> NULL<span class="op">,</span> <span class="st">"label"</span><span class="op">);</span></span>
|
||
<span id="cb6-13"><a href="#cb6-13"></a> <span class="co">/* Evaluate the expression */</span></span>
|
||
<span id="cb6-14"><a href="#cb6-14"></a> <span class="cf">if</span> <span class="op">(</span>gtk_expression_evaluate <span class="op">(</span>expression<span class="op">,</span> label<span class="op">,</span> <span class="op">&</span>value<span class="op">))</span></span>
|
||
<span id="cb6-15"><a href="#cb6-15"></a> g_print <span class="op">(</span><span class="st">"The value is %s.</span><span class="sc">\n</span><span class="st">"</span><span class="op">,</span> g_value_get_string <span class="op">(&</span>value<span class="op">));</span></span>
|
||
<span id="cb6-16"><a href="#cb6-16"></a> <span class="cf">else</span></span>
|
||
<span id="cb6-17"><a href="#cb6-17"></a> g_print <span class="op">(</span><span class="st">"The property expression wasn't evaluated correctly.</span><span class="sc">\n</span><span class="st">"</span><span class="op">);</span></span>
|
||
<span id="cb6-18"><a href="#cb6-18"></a> gtk_expression_unref <span class="op">(</span>expression<span class="op">);</span></span>
|
||
<span id="cb6-19"><a href="#cb6-19"></a> g_value_unset <span class="op">(&</span>value<span class="op">);</span></span>
|
||
<span id="cb6-20"><a href="#cb6-20"></a></span>
|
||
<span id="cb6-21"><a href="#cb6-21"></a> <span class="cf">return</span> <span class="dv">0</span><span class="op">;</span></span>
|
||
<span id="cb6-22"><a href="#cb6-22"></a><span class="op">}</span></span></code></pre></div>
|
||
<ul>
|
||
<li>9-10: <code>gtk_init</code> initializes GTK GUI toolkit. It isn’t
|
||
usually necessary because the GtkApplication default startup handler
|
||
does the initialization. A GtkLabel instance is created with the text
|
||
“Hello world.”.</li>
|
||
<li>12: A property expression is created. It looks a “label” property of
|
||
a GtkLabel instance. But at the creation, no instance is given because
|
||
the second argument is NULL. The expression just knows how to take the
|
||
property from a future-given GtkLabel instance.</li>
|
||
<li>14-17: The function <code>gtk_expression_evaluate</code> evaluates
|
||
the expression with a ‘this’ instance <code>label</code>. The result is
|
||
stored in the GValue <code>value</code>. The function
|
||
<code>g_value_get_string</code> gets a string from the GValue. But the
|
||
string is owned by the GValue so you must not free the string.</li>
|
||
<li>18-19: Releases the expression and unset the GValue. At the same
|
||
time the string in the GValue is freed.</li>
|
||
</ul>
|
||
<p>If the second argument of <code>gtk_property_expression_new</code>
|
||
isn’t NULL, it is another expression. The expression is owned by a newly
|
||
created property expression. So, when the expressions are useless, you
|
||
just release the last expression. Then it releases another expression it
|
||
has.</p>
|
||
<h2 id="closure-expression">Closure expression</h2>
|
||
<p>A closure expression calls closure when it is evaluated. A closure is
|
||
a generic representation of a callback (a pointer to a function). For
|
||
information about closure, see <a
|
||
href="https://docs.gtk.org/gobject/concepts.html#the-gobject-messaging-system">GObject
|
||
API Reference – The GObject messaging system</a>. There are simple
|
||
closure example files <code>closure.c</code> and
|
||
<code>closure_each.c</code> in the <code>src/expression</code>
|
||
directory.</p>
|
||
<p>There are two types of closure expressions, GtkCClosureExpression and
|
||
GtkClosureExpression. They corresponds to GCClosure and GClosure
|
||
respectively. When you program in C language, GtkCClosureExpression and
|
||
GCClosure are appropriate.</p>
|
||
<p>A closure expression is created with
|
||
<code>gtk_cclosure_expression_new</code> function.</p>
|
||
<div class="sourceCode" id="cb7"><pre class="sourceCode C"><code class="sourceCode c"><span id="cb7-1"><a href="#cb7-1" aria-hidden="true" tabindex="-1"></a><span class="dt">int</span></span>
|
||
<span id="cb7-2"><a href="#cb7-2" aria-hidden="true" tabindex="-1"></a>callback <span class="op">(</span>GObject <span class="op">*</span>object<span class="op">,</span> <span class="dt">int</span> x<span class="op">,</span> <span class="dt">const</span> <span class="dt">char</span> <span class="op">*</span>s<span class="op">)</span></span></code></pre></div>
|
||
<p>The following is <code>exp_closure_simple.c</code> in
|
||
<code>src/expression</code>.</p>
|
||
<div class="sourceCode" id="cb8"><pre
|
||
class="sourceCode numberSource C numberLines"><code class="sourceCode c"><span id="cb8-1"><a href="#cb8-1"></a><span class="pp">#include </span><span class="im"><gtk/gtk.h></span></span>
|
||
<span id="cb8-2"><a href="#cb8-2"></a></span>
|
||
<span id="cb8-3"><a href="#cb8-3"></a><span class="dt">static</span> <span class="dt">int</span></span>
|
||
<span id="cb8-4"><a href="#cb8-4"></a>calc <span class="op">(</span>GtkLabel <span class="op">*</span>label<span class="op">)</span> <span class="op">{</span> <span class="co">/* this object */</span></span>
|
||
<span id="cb8-5"><a href="#cb8-5"></a> <span class="dt">const</span> <span class="dt">char</span> <span class="op">*</span> s<span class="op">;</span></span>
|
||
<span id="cb8-6"><a href="#cb8-6"></a> <span class="dt">int</span> i<span class="op">,</span> j<span class="op">;</span></span>
|
||
<span id="cb8-7"><a href="#cb8-7"></a></span>
|
||
<span id="cb8-8"><a href="#cb8-8"></a> s <span class="op">=</span> gtk_label_get_text <span class="op">(</span>label<span class="op">);</span> <span class="co">/* s is owned by the label. */</span></span>
|
||
<span id="cb8-9"><a href="#cb8-9"></a> sscanf <span class="op">(</span>s<span class="op">,</span> <span class="st">"%d+%d"</span><span class="op">,</span> <span class="op">&</span>i<span class="op">,</span> <span class="op">&</span>j<span class="op">);</span></span>
|
||
<span id="cb8-10"><a href="#cb8-10"></a> <span class="cf">return</span> i<span class="op">+</span>j<span class="op">;</span></span>
|
||
<span id="cb8-11"><a href="#cb8-11"></a><span class="op">}</span></span>
|
||
<span id="cb8-12"><a href="#cb8-12"></a></span>
|
||
<span id="cb8-13"><a href="#cb8-13"></a><span class="dt">int</span></span>
|
||
<span id="cb8-14"><a href="#cb8-14"></a>main <span class="op">(</span><span class="dt">int</span> argc<span class="op">,</span> <span class="dt">char</span> <span class="op">**</span>argv<span class="op">)</span> <span class="op">{</span></span>
|
||
<span id="cb8-15"><a href="#cb8-15"></a> GtkExpression <span class="op">*</span>expression<span class="op">;</span></span>
|
||
<span id="cb8-16"><a href="#cb8-16"></a> GValue value <span class="op">=</span> G_VALUE_INIT<span class="op">;</span></span>
|
||
<span id="cb8-17"><a href="#cb8-17"></a> GtkLabel <span class="op">*</span>label<span class="op">;</span></span>
|
||
<span id="cb8-18"><a href="#cb8-18"></a></span>
|
||
<span id="cb8-19"><a href="#cb8-19"></a> gtk_init <span class="op">();</span></span>
|
||
<span id="cb8-20"><a href="#cb8-20"></a> label <span class="op">=</span> GTK_LABEL <span class="op">(</span>gtk_label_new <span class="op">(</span><span class="st">"123+456"</span><span class="op">));</span></span>
|
||
<span id="cb8-21"><a href="#cb8-21"></a> g_object_ref_sink <span class="op">(</span>label<span class="op">);</span></span>
|
||
<span id="cb8-22"><a href="#cb8-22"></a> expression <span class="op">=</span> gtk_cclosure_expression_new <span class="op">(</span>G_TYPE_INT<span class="op">,</span> NULL<span class="op">,</span> <span class="dv">0</span><span class="op">,</span> NULL<span class="op">,</span></span>
|
||
<span id="cb8-23"><a href="#cb8-23"></a> G_CALLBACK <span class="op">(</span>calc<span class="op">),</span> NULL<span class="op">,</span> NULL<span class="op">);</span></span>
|
||
<span id="cb8-24"><a href="#cb8-24"></a> <span class="cf">if</span> <span class="op">(</span>gtk_expression_evaluate <span class="op">(</span>expression<span class="op">,</span> label<span class="op">,</span> <span class="op">&</span>value<span class="op">))</span> <span class="co">/* 'this' object is the label. */</span></span>
|
||
<span id="cb8-25"><a href="#cb8-25"></a> g_print <span class="op">(</span><span class="st">"%d</span><span class="sc">\n</span><span class="st">"</span><span class="op">,</span> g_value_get_int <span class="op">(&</span>value<span class="op">));</span></span>
|
||
<span id="cb8-26"><a href="#cb8-26"></a> <span class="cf">else</span></span>
|
||
<span id="cb8-27"><a href="#cb8-27"></a> g_print <span class="op">(</span><span class="st">"The closure expression wasn't evaluated correctly.</span><span class="sc">\n</span><span class="st">"</span><span class="op">);</span></span>
|
||
<span id="cb8-28"><a href="#cb8-28"></a> gtk_expression_unref <span class="op">(</span>expression<span class="op">);</span></span>
|
||
<span id="cb8-29"><a href="#cb8-29"></a> g_value_unset <span class="op">(&</span>value<span class="op">);</span></span>
|
||
<span id="cb8-30"><a href="#cb8-30"></a> g_object_unref <span class="op">(</span>label<span class="op">);</span></span>
|
||
<span id="cb8-31"><a href="#cb8-31"></a> </span>
|
||
<span id="cb8-32"><a href="#cb8-32"></a> <span class="cf">return</span> <span class="dv">0</span><span class="op">;</span></span>
|
||
<span id="cb8-33"><a href="#cb8-33"></a><span class="op">}</span></span></code></pre></div>
|
||
<ul>
|
||
<li>3-11: A call back function. The parameter is only one and it is a
|
||
‘this’ object. It is a GtkLabel and its label is assumed to be
|
||
“(number)+(number)”.</li>
|
||
<li>8-10: Retrieves two integers from the label and returns the sum of
|
||
them. This function has no error report. If you want to return error
|
||
report, change the return value type to be a pointer to a structure of
|
||
gboolean and integer. One for error and the other for the sum. The first
|
||
argument of <code>gtk_cclosure_expression_new</code> is
|
||
<code>G_TYPE_POINTER</code>. There is a sample program
|
||
<code>exp_closure_with_error_report</code> in
|
||
<code>src/expression</code> directory.</li>
|
||
<li>19: The function `gtk_init`` initializes GTK. It is necessary for
|
||
GtkLabel.</li>
|
||
<li>20: A GtkLabel instance is created with “123+456”.</li>
|
||
<li>21: The instance has floating reference. It is changed to an
|
||
ordinary reference count.</li>
|
||
<li>22-23: Creates a closure expression. Its return value type is
|
||
<code>G_TYPE_INT</code> and no parameters or ‘this’ object.</li>
|
||
<li>24: Evaluates the expression with the label as a ‘this’ object.</li>
|
||
<li>25: If the evaluation successes, the sum of “123+456”, which is 579,
|
||
is shown.</li>
|
||
<li>27: If it fails, an error message appears.</li>
|
||
<li>28-30: Releases the expression and the label. Unsets the value.</li>
|
||
</ul>
|
||
<p>Closure expression is flexible than other type of expression because
|
||
you can specify your own callback function.</p>
|
||
<h2 id="gtkexpressionwatch">GtkExpressionWatch</h2>
|
||
<p>GtkExpressionWatch is a structure, not an object. It represents a
|
||
watched GtkExpression. Two functions create GtkExpressionWatch
|
||
structure. They are <code>gtk_expression_bind</code> and
|
||
<code>gtk_expression_watch</code>.</p>
|
||
<h3 id="gtk_expression_bind-function">gtk_expression_bind function</h3>
|
||
<p>This function binds the target object’s property to the expression.
|
||
If the value of the expression changes, the property reflects the value
|
||
immediately.</p>
|
||
<div class="sourceCode" id="cb9"><pre class="sourceCode C"><code class="sourceCode c"><span id="cb9-1"><a href="#cb9-1" aria-hidden="true" tabindex="-1"></a>GtkExpressionWatch<span class="op">*</span></span>
|
||
<span id="cb9-2"><a href="#cb9-2" aria-hidden="true" tabindex="-1"></a>gtk_expression_bind <span class="op">(</span></span>
|
||
<span id="cb9-3"><a href="#cb9-3" aria-hidden="true" tabindex="-1"></a> GtkExpression<span class="op">*</span> self<span class="op">,</span></span>
|
||
<span id="cb9-4"><a href="#cb9-4" aria-hidden="true" tabindex="-1"></a> GObject<span class="op">*</span> target<span class="op">,</span></span>
|
||
<span id="cb9-5"><a href="#cb9-5" aria-hidden="true" tabindex="-1"></a> <span class="dt">const</span> <span class="dt">char</span><span class="op">*</span> property<span class="op">,</span></span>
|
||
<span id="cb9-6"><a href="#cb9-6" aria-hidden="true" tabindex="-1"></a> GObject<span class="op">*</span> this_</span>
|
||
<span id="cb9-7"><a href="#cb9-7" aria-hidden="true" tabindex="-1"></a><span class="op">)</span></span></code></pre></div>
|
||
<p>This function takes the ownership of the expression. So, if you want
|
||
to own the expression, call <code>gtk_expression_ref ()</code> to
|
||
increase the reference count of the expression. And you should unref it
|
||
when it is useless. If you don’t own the expression, you don’t care
|
||
about releasing the expression.</p>
|
||
<p>An example <code>exp_bind.c</code> and <code>exp_bind.ui</code> is in
|
||
<code>src/expression</code> directory.</p>
|
||
<figure>
|
||
<img src="image/exp_bind.png" alt="exp_bind" />
|
||
<figcaption aria-hidden="true">exp_bind</figcaption>
|
||
</figure>
|
||
<p>It includes a label and a scale. If you move the slider to the right,
|
||
the scale value increases and the number on the label also increases. In
|
||
the same way, if you move it to the left, the number on the label
|
||
decreases. The label is bound to the scale value via an adjustment.</p>
|
||
<div class="sourceCode" id="cb10"><pre
|
||
class="sourceCode numberSource xml numberLines"><code class="sourceCode xml"><span id="cb10-1"><a href="#cb10-1"></a><span class="fu"><?xml</span><span class="ot"> version=</span><span class="st">'1.0'</span><span class="ot"> encoding=</span><span class="st">'UTF-8'</span><span class="fu">?></span></span>
|
||
<span id="cb10-2"><a href="#cb10-2"></a><<span class="kw">interface</span>></span>
|
||
<span id="cb10-3"><a href="#cb10-3"></a> <<span class="kw">object</span><span class="ot"> class=</span><span class="st">'GtkApplicationWindow'</span><span class="ot"> id=</span><span class="st">'win'</span>></span>
|
||
<span id="cb10-4"><a href="#cb10-4"></a> <<span class="kw">property</span><span class="ot"> name=</span><span class="st">'default-width'</span>>600</<span class="kw">property</span>></span>
|
||
<span id="cb10-5"><a href="#cb10-5"></a> <<span class="kw">child</span>></span>
|
||
<span id="cb10-6"><a href="#cb10-6"></a> <<span class="kw">object</span><span class="ot"> class=</span><span class="st">'GtkBox'</span>></span>
|
||
<span id="cb10-7"><a href="#cb10-7"></a> <<span class="kw">property</span><span class="ot"> name=</span><span class="st">'orientation'</span>>GTK_ORIENTATION_VERTICAL</<span class="kw">property</span>></span>
|
||
<span id="cb10-8"><a href="#cb10-8"></a> <<span class="kw">child</span>></span>
|
||
<span id="cb10-9"><a href="#cb10-9"></a> <<span class="kw">object</span><span class="ot"> class=</span><span class="st">'GtkLabel'</span><span class="ot"> id=</span><span class="st">'label'</span>></span>
|
||
<span id="cb10-10"><a href="#cb10-10"></a> <<span class="kw">property</span><span class="ot"> name=</span><span class="st">"label"</span>>10</<span class="kw">property</span>></span>
|
||
<span id="cb10-11"><a href="#cb10-11"></a> </<span class="kw">object</span>></span>
|
||
<span id="cb10-12"><a href="#cb10-12"></a> </<span class="kw">child</span>></span>
|
||
<span id="cb10-13"><a href="#cb10-13"></a> <<span class="kw">child</span>></span>
|
||
<span id="cb10-14"><a href="#cb10-14"></a> <<span class="kw">object</span><span class="ot"> class=</span><span class="st">'GtkScale'</span>></span>
|
||
<span id="cb10-15"><a href="#cb10-15"></a> <<span class="kw">property</span><span class="ot"> name=</span><span class="st">'adjustment'</span>></span>
|
||
<span id="cb10-16"><a href="#cb10-16"></a> <<span class="kw">object</span><span class="ot"> class=</span><span class="st">'GtkAdjustment'</span><span class="ot"> id=</span><span class="st">'adjustment'</span>></span>
|
||
<span id="cb10-17"><a href="#cb10-17"></a> <<span class="kw">property</span><span class="ot"> name=</span><span class="st">'upper'</span>>20.0</<span class="kw">property</span>></span>
|
||
<span id="cb10-18"><a href="#cb10-18"></a> <<span class="kw">property</span><span class="ot"> name=</span><span class="st">'lower'</span>>0.0</<span class="kw">property</span>></span>
|
||
<span id="cb10-19"><a href="#cb10-19"></a> <<span class="kw">property</span><span class="ot"> name=</span><span class="st">'value'</span>>10.0</<span class="kw">property</span>></span>
|
||
<span id="cb10-20"><a href="#cb10-20"></a> <<span class="kw">property</span><span class="ot"> name=</span><span class="st">'step-increment'</span>>1.0</<span class="kw">property</span>></span>
|
||
<span id="cb10-21"><a href="#cb10-21"></a> <<span class="kw">property</span><span class="ot"> name=</span><span class="st">'page-increment'</span>>5.0</<span class="kw">property</span>></span>
|
||
<span id="cb10-22"><a href="#cb10-22"></a> <<span class="kw">property</span><span class="ot"> name=</span><span class="st">'page-size'</span>>0.0</<span class="kw">property</span>></span>
|
||
<span id="cb10-23"><a href="#cb10-23"></a> </<span class="kw">object</span>></span>
|
||
<span id="cb10-24"><a href="#cb10-24"></a> </<span class="kw">property</span>></span>
|
||
<span id="cb10-25"><a href="#cb10-25"></a> <<span class="kw">property</span><span class="ot"> name=</span><span class="st">'digits'</span>>0</<span class="kw">property</span>></span>
|
||
<span id="cb10-26"><a href="#cb10-26"></a> <<span class="kw">property</span><span class="ot"> name=</span><span class="st">'draw-value'</span>>true</<span class="kw">property</span>></span>
|
||
<span id="cb10-27"><a href="#cb10-27"></a> <<span class="kw">property</span><span class="ot"> name=</span><span class="st">'has-origin'</span>>true</<span class="kw">property</span>></span>
|
||
<span id="cb10-28"><a href="#cb10-28"></a> <<span class="kw">property</span><span class="ot"> name=</span><span class="st">'round-digits'</span>>0</<span class="kw">property</span>></span>
|
||
<span id="cb10-29"><a href="#cb10-29"></a> </<span class="kw">object</span>></span>
|
||
<span id="cb10-30"><a href="#cb10-30"></a> </<span class="kw">child</span>></span>
|
||
<span id="cb10-31"><a href="#cb10-31"></a> </<span class="kw">object</span>></span>
|
||
<span id="cb10-32"><a href="#cb10-32"></a> </<span class="kw">child</span>></span>
|
||
<span id="cb10-33"><a href="#cb10-33"></a> </<span class="kw">object</span>></span>
|
||
<span id="cb10-34"><a href="#cb10-34"></a></<span class="kw">interface</span>></span></code></pre></div>
|
||
<p>The ui file describes the following parent-child relationship.</p>
|
||
<pre><code>GtkApplicationWindow (win) -- GtkBox -+- GtkLabel (label)
|
||
+- GtkScale</code></pre>
|
||
<p>Four GtkScale properties are defined.</p>
|
||
<ul>
|
||
<li>adjustment. GtkAdjustment provides the followings.
|
||
<ul>
|
||
<li>upper and lower: the range of the scale.</li>
|
||
<li>value: current value of the scale. It reflects the value of the
|
||
scale.</li>
|
||
<li>step increment and page increment: When a user press an arrow key or
|
||
page up/down key, the scale moves by the step increment or page
|
||
increment respectively.</li>
|
||
<li>page-size: When an adjustment is used with a scale, page-size is
|
||
zero.</li>
|
||
</ul></li>
|
||
<li>digits: The number of decimal places that are displayed in the
|
||
value.</li>
|
||
<li>draw-value: Whether the value is displayed.</li>
|
||
<li>has-origin: Whether the scale has the origin. If it’s true, an
|
||
orange bar appears between the origin and the current point.</li>
|
||
<li>round-digits: The number of digits to round the value to when it
|
||
changes. For example, if it is zero, the slider moves to an integer
|
||
point.</li>
|
||
</ul>
|
||
<div class="sourceCode" id="cb12"><pre
|
||
class="sourceCode numberSource C numberLines"><code class="sourceCode c"><span id="cb12-1"><a href="#cb12-1"></a><span class="pp">#include </span><span class="im"><gtk/gtk.h></span></span>
|
||
<span id="cb12-2"><a href="#cb12-2"></a></span>
|
||
<span id="cb12-3"><a href="#cb12-3"></a>GtkExpressionWatch <span class="op">*</span>watch<span class="op">;</span></span>
|
||
<span id="cb12-4"><a href="#cb12-4"></a></span>
|
||
<span id="cb12-5"><a href="#cb12-5"></a><span class="dt">static</span> <span class="dt">int</span></span>
|
||
<span id="cb12-6"><a href="#cb12-6"></a>f2i <span class="op">(</span>GObject <span class="op">*</span>object<span class="op">,</span> <span class="dt">double</span> d<span class="op">)</span> <span class="op">{</span></span>
|
||
<span id="cb12-7"><a href="#cb12-7"></a> <span class="cf">return</span> <span class="op">(</span><span class="dt">int</span><span class="op">)</span> d<span class="op">;</span></span>
|
||
<span id="cb12-8"><a href="#cb12-8"></a><span class="op">}</span></span>
|
||
<span id="cb12-9"><a href="#cb12-9"></a></span>
|
||
<span id="cb12-10"><a href="#cb12-10"></a><span class="dt">static</span> <span class="dt">int</span></span>
|
||
<span id="cb12-11"><a href="#cb12-11"></a>close_request_cb <span class="op">(</span>GtkWindow <span class="op">*</span>win<span class="op">)</span> <span class="op">{</span></span>
|
||
<span id="cb12-12"><a href="#cb12-12"></a> gtk_expression_watch_unwatch <span class="op">(</span>watch<span class="op">);</span></span>
|
||
<span id="cb12-13"><a href="#cb12-13"></a> <span class="cf">return</span> false<span class="op">;</span></span>
|
||
<span id="cb12-14"><a href="#cb12-14"></a><span class="op">}</span></span>
|
||
<span id="cb12-15"><a href="#cb12-15"></a></span>
|
||
<span id="cb12-16"><a href="#cb12-16"></a><span class="dt">static</span> <span class="dt">void</span></span>
|
||
<span id="cb12-17"><a href="#cb12-17"></a>app_activate <span class="op">(</span>GApplication <span class="op">*</span>application<span class="op">)</span> <span class="op">{</span></span>
|
||
<span id="cb12-18"><a href="#cb12-18"></a> GtkApplication <span class="op">*</span>app <span class="op">=</span> GTK_APPLICATION <span class="op">(</span>application<span class="op">);</span></span>
|
||
<span id="cb12-19"><a href="#cb12-19"></a> gtk_window_present <span class="op">(</span>gtk_application_get_active_window<span class="op">(</span>app<span class="op">));</span></span>
|
||
<span id="cb12-20"><a href="#cb12-20"></a><span class="op">}</span></span>
|
||
<span id="cb12-21"><a href="#cb12-21"></a></span>
|
||
<span id="cb12-22"><a href="#cb12-22"></a><span class="dt">static</span> <span class="dt">void</span></span>
|
||
<span id="cb12-23"><a href="#cb12-23"></a>app_startup <span class="op">(</span>GApplication <span class="op">*</span>application<span class="op">)</span> <span class="op">{</span></span>
|
||
<span id="cb12-24"><a href="#cb12-24"></a> GtkApplication <span class="op">*</span>app <span class="op">=</span> GTK_APPLICATION <span class="op">(</span>application<span class="op">);</span></span>
|
||
<span id="cb12-25"><a href="#cb12-25"></a> GtkBuilder <span class="op">*</span>build<span class="op">;</span></span>
|
||
<span id="cb12-26"><a href="#cb12-26"></a> GtkWidget <span class="op">*</span>win<span class="op">,</span> <span class="op">*</span>label<span class="op">;</span></span>
|
||
<span id="cb12-27"><a href="#cb12-27"></a> GtkAdjustment <span class="op">*</span>adjustment<span class="op">;</span></span>
|
||
<span id="cb12-28"><a href="#cb12-28"></a> GtkExpression <span class="op">*</span>expression<span class="op">,</span> <span class="op">*</span>params<span class="op">[</span><span class="dv">1</span><span class="op">];</span></span>
|
||
<span id="cb12-29"><a href="#cb12-29"></a></span>
|
||
<span id="cb12-30"><a href="#cb12-30"></a> <span class="co">/* Builds a window with exp.ui resource */</span></span>
|
||
<span id="cb12-31"><a href="#cb12-31"></a> build <span class="op">=</span> gtk_builder_new_from_resource <span class="op">(</span><span class="st">"/com/github/ToshioCP/exp/exp_bind.ui"</span><span class="op">);</span></span>
|
||
<span id="cb12-32"><a href="#cb12-32"></a> win <span class="op">=</span> GTK_WIDGET <span class="op">(</span>gtk_builder_get_object <span class="op">(</span>build<span class="op">,</span> <span class="st">"win"</span><span class="op">));</span></span>
|
||
<span id="cb12-33"><a href="#cb12-33"></a> label <span class="op">=</span> GTK_WIDGET <span class="op">(</span>gtk_builder_get_object <span class="op">(</span>build<span class="op">,</span> <span class="st">"label"</span><span class="op">));</span></span>
|
||
<span id="cb12-34"><a href="#cb12-34"></a> <span class="co">// scale = GTK_WIDGET (gtk_builder_get_object (build, "scale"));</span></span>
|
||
<span id="cb12-35"><a href="#cb12-35"></a> adjustment <span class="op">=</span> GTK_ADJUSTMENT <span class="op">(</span>gtk_builder_get_object <span class="op">(</span>build<span class="op">,</span> <span class="st">"adjustment"</span><span class="op">));</span></span>
|
||
<span id="cb12-36"><a href="#cb12-36"></a> gtk_window_set_application <span class="op">(</span>GTK_WINDOW <span class="op">(</span>win<span class="op">),</span> app<span class="op">);</span></span>
|
||
<span id="cb12-37"><a href="#cb12-37"></a> g_signal_connect <span class="op">(</span>win<span class="op">,</span> <span class="st">"close-request"</span><span class="op">,</span> G_CALLBACK <span class="op">(</span>close_request_cb<span class="op">),</span> NULL<span class="op">);</span></span>
|
||
<span id="cb12-38"><a href="#cb12-38"></a> g_object_unref <span class="op">(</span>build<span class="op">);</span></span>
|
||
<span id="cb12-39"><a href="#cb12-39"></a></span>
|
||
<span id="cb12-40"><a href="#cb12-40"></a> <span class="co">/* GtkExpressionWatch */</span></span>
|
||
<span id="cb12-41"><a href="#cb12-41"></a> params<span class="op">[</span><span class="dv">0</span><span class="op">]</span> <span class="op">=</span> gtk_property_expression_new <span class="op">(</span>GTK_TYPE_ADJUSTMENT<span class="op">,</span> NULL<span class="op">,</span> <span class="st">"value"</span><span class="op">);</span></span>
|
||
<span id="cb12-42"><a href="#cb12-42"></a> expression <span class="op">=</span> gtk_cclosure_expression_new <span class="op">(</span>G_TYPE_INT<span class="op">,</span> NULL<span class="op">,</span> <span class="dv">1</span><span class="op">,</span> params<span class="op">,</span> G_CALLBACK <span class="op">(</span>f2i<span class="op">),</span> NULL<span class="op">,</span> NULL<span class="op">);</span></span>
|
||
<span id="cb12-43"><a href="#cb12-43"></a> watch <span class="op">=</span> gtk_expression_bind <span class="op">(</span>expression<span class="op">,</span> label<span class="op">,</span> <span class="st">"label"</span><span class="op">,</span> adjustment<span class="op">);</span> <span class="co">/* watch takes the ownership of the expression. */</span></span>
|
||
<span id="cb12-44"><a href="#cb12-44"></a><span class="op">}</span></span>
|
||
<span id="cb12-45"><a href="#cb12-45"></a></span>
|
||
<span id="cb12-46"><a href="#cb12-46"></a><span class="pp">#define APPLICATION_ID "com.github.ToshioCP.exp_watch"</span></span>
|
||
<span id="cb12-47"><a href="#cb12-47"></a></span>
|
||
<span id="cb12-48"><a href="#cb12-48"></a><span class="dt">int</span></span>
|
||
<span id="cb12-49"><a href="#cb12-49"></a>main <span class="op">(</span><span class="dt">int</span> argc<span class="op">,</span> <span class="dt">char</span> <span class="op">**</span>argv<span class="op">)</span> <span class="op">{</span></span>
|
||
<span id="cb12-50"><a href="#cb12-50"></a> GtkApplication <span class="op">*</span>app<span class="op">;</span></span>
|
||
<span id="cb12-51"><a href="#cb12-51"></a> <span class="dt">int</span> stat<span class="op">;</span></span>
|
||
<span id="cb12-52"><a href="#cb12-52"></a></span>
|
||
<span id="cb12-53"><a href="#cb12-53"></a> app <span class="op">=</span> gtk_application_new <span class="op">(</span>APPLICATION_ID<span class="op">,</span> G_APPLICATION_DEFAULT_FLAGS<span class="op">);</span></span>
|
||
<span id="cb12-54"><a href="#cb12-54"></a></span>
|
||
<span id="cb12-55"><a href="#cb12-55"></a> g_signal_connect <span class="op">(</span>app<span class="op">,</span> <span class="st">"startup"</span><span class="op">,</span> G_CALLBACK <span class="op">(</span>app_startup<span class="op">),</span> NULL<span class="op">);</span></span>
|
||
<span id="cb12-56"><a href="#cb12-56"></a> g_signal_connect <span class="op">(</span>app<span class="op">,</span> <span class="st">"activate"</span><span class="op">,</span> G_CALLBACK <span class="op">(</span>app_activate<span class="op">),</span> NULL<span class="op">);</span></span>
|
||
<span id="cb12-57"><a href="#cb12-57"></a></span>
|
||
<span id="cb12-58"><a href="#cb12-58"></a> stat <span class="op">=</span>g_application_run <span class="op">(</span>G_APPLICATION <span class="op">(</span>app<span class="op">),</span> argc<span class="op">,</span> argv<span class="op">);</span></span>
|
||
<span id="cb12-59"><a href="#cb12-59"></a> g_object_unref <span class="op">(</span>app<span class="op">);</span></span>
|
||
<span id="cb12-60"><a href="#cb12-60"></a> <span class="cf">return</span> stat<span class="op">;</span></span>
|
||
<span id="cb12-61"><a href="#cb12-61"></a><span class="op">}</span></span></code></pre></div>
|
||
<p>The point of the program is:</p>
|
||
<ul>
|
||
<li>41-42: Two expressions are defined. One is a property expression and
|
||
the other is a closure expression. The property expression looks up the
|
||
“value” property of the adjustment instance. The closure expression just
|
||
converts the double into an integer.</li>
|
||
<li>43: <code>gtk_expression_bind</code> binds the label property of the
|
||
GtkLabel instance to the integer returned by the closure expression. It
|
||
creates a GtkExpressionWatch structure. The binding works during the
|
||
watch lives. When the window is destroyed, the scale and adjustment are
|
||
also destroyed. And the watch recognizes the value of the expression
|
||
changes and tries to change the property of the label. Obviously, it is
|
||
not a correct behavior. The watch should be unwatched before the window
|
||
is destroyed.</li>
|
||
<li>37: Connects the “close-request” signal on the window to a handler
|
||
<code>close_request_cb</code>. This signal is emitted when the close
|
||
button is clicked. The handler is called just before the window closes.
|
||
It is the right moment to make the GtkExpressionWatch unwatched.</li>
|
||
<li>10-14: “close-request” signal handler. The function
|
||
<code>gtk_expression_watch_unwatch (watch)</code> makes the watch stop
|
||
watching the expression. It also releases the expression.</li>
|
||
</ul>
|
||
<p>If you want to bind a property to an expression,
|
||
<code>gtk_expression_bind</code> is the best choice. You can do it with
|
||
<code>gtk_expression_watch</code> function, but it is less suitable.</p>
|
||
<h3 id="gtk_expression_watch-function">gtk_expression_watch
|
||
function</h3>
|
||
<div class="sourceCode" id="cb13"><pre class="sourceCode C"><code class="sourceCode c"><span id="cb13-1"><a href="#cb13-1" aria-hidden="true" tabindex="-1"></a>GtkExpressionWatch<span class="op">*</span></span>
|
||
<span id="cb13-2"><a href="#cb13-2" aria-hidden="true" tabindex="-1"></a>gtk_expression_watch <span class="op">(</span></span>
|
||
<span id="cb13-3"><a href="#cb13-3" aria-hidden="true" tabindex="-1"></a> GtkExpression<span class="op">*</span> self<span class="op">,</span></span>
|
||
<span id="cb13-4"><a href="#cb13-4" aria-hidden="true" tabindex="-1"></a> GObject<span class="op">*</span> this_<span class="op">,</span></span>
|
||
<span id="cb13-5"><a href="#cb13-5" aria-hidden="true" tabindex="-1"></a> GtkExpressionNotify notify<span class="op">,</span></span>
|
||
<span id="cb13-6"><a href="#cb13-6" aria-hidden="true" tabindex="-1"></a> gpointer user_data<span class="op">,</span></span>
|
||
<span id="cb13-7"><a href="#cb13-7" aria-hidden="true" tabindex="-1"></a> GDestroyNotify user_destroy</span>
|
||
<span id="cb13-8"><a href="#cb13-8" aria-hidden="true" tabindex="-1"></a><span class="op">)</span></span></code></pre></div>
|
||
<p>The function doesn’t take the ownership of the expression. It differs
|
||
from <code>gtk_expression_bind</code>. So, you need to release the
|
||
expression when it is useless. It creates a GtkExpressionWatch
|
||
structure. The third parameter <code>notify</code> is a callback to
|
||
invoke when the expression changes. You can set <code>user_data</code>
|
||
to give it to the callback. The last parameter is a function to destroy
|
||
the <code>user_data</code> when the watch is unwatched. Put NULL if you
|
||
don’t need them.</p>
|
||
<p>Notify callback has the following format.</p>
|
||
<div class="sourceCode" id="cb14"><pre class="sourceCode C"><code class="sourceCode c"><span id="cb14-1"><a href="#cb14-1" aria-hidden="true" tabindex="-1"></a><span class="dt">void</span></span>
|
||
<span id="cb14-2"><a href="#cb14-2" aria-hidden="true" tabindex="-1"></a>notify <span class="op">(</span></span>
|
||
<span id="cb14-3"><a href="#cb14-3" aria-hidden="true" tabindex="-1"></a> gpointer user_data</span>
|
||
<span id="cb14-4"><a href="#cb14-4" aria-hidden="true" tabindex="-1"></a><span class="op">)</span></span></code></pre></div>
|
||
<p>This function is used to do something when the value of the
|
||
expression changes. But if you want to bind a property to the value, use
|
||
<code>gtk_expression_bind</code> instead.</p>
|
||
<p>There’s a sample program <code>exp_watch.c</code> in
|
||
<code>src/expression</code> directory. It outputs the width of the
|
||
window to the standard output.</p>
|
||
<figure>
|
||
<img src="image/exp_watch.png" alt="exp_watch" />
|
||
<figcaption aria-hidden="true">exp_watch</figcaption>
|
||
</figure>
|
||
<p>When you resize the window, the width is displayed in the
|
||
terminal.</p>
|
||
<div class="sourceCode" id="cb15"><pre
|
||
class="sourceCode numberSource C numberLines"><code class="sourceCode c"><span id="cb15-1"><a href="#cb15-1"></a><span class="pp">#include </span><span class="im"><gtk/gtk.h></span></span>
|
||
<span id="cb15-2"><a href="#cb15-2"></a></span>
|
||
<span id="cb15-3"><a href="#cb15-3"></a>GtkExpression <span class="op">*</span>expression<span class="op">;</span></span>
|
||
<span id="cb15-4"><a href="#cb15-4"></a>GtkExpressionWatch <span class="op">*</span>watch<span class="op">;</span></span>
|
||
<span id="cb15-5"><a href="#cb15-5"></a></span>
|
||
<span id="cb15-6"><a href="#cb15-6"></a><span class="dt">static</span> <span class="dt">void</span></span>
|
||
<span id="cb15-7"><a href="#cb15-7"></a>notify <span class="op">(</span>gpointer user_data<span class="op">)</span> <span class="op">{</span></span>
|
||
<span id="cb15-8"><a href="#cb15-8"></a> GValue value <span class="op">=</span> G_VALUE_INIT<span class="op">;</span></span>
|
||
<span id="cb15-9"><a href="#cb15-9"></a></span>
|
||
<span id="cb15-10"><a href="#cb15-10"></a> <span class="cf">if</span> <span class="op">(</span>gtk_expression_watch_evaluate <span class="op">(</span>watch<span class="op">,</span> <span class="op">&</span>value<span class="op">))</span></span>
|
||
<span id="cb15-11"><a href="#cb15-11"></a> g_print <span class="op">(</span><span class="st">"width = %d</span><span class="sc">\n</span><span class="st">"</span><span class="op">,</span> g_value_get_int <span class="op">(&</span>value<span class="op">));</span></span>
|
||
<span id="cb15-12"><a href="#cb15-12"></a> <span class="cf">else</span></span>
|
||
<span id="cb15-13"><a href="#cb15-13"></a> g_print <span class="op">(</span><span class="st">"evaluation failed.</span><span class="sc">\n</span><span class="st">"</span><span class="op">);</span></span>
|
||
<span id="cb15-14"><a href="#cb15-14"></a><span class="op">}</span></span>
|
||
<span id="cb15-15"><a href="#cb15-15"></a></span>
|
||
<span id="cb15-16"><a href="#cb15-16"></a><span class="dt">static</span> <span class="dt">int</span></span>
|
||
<span id="cb15-17"><a href="#cb15-17"></a>close_request_cb <span class="op">(</span>GtkWindow <span class="op">*</span>win<span class="op">)</span> <span class="op">{</span></span>
|
||
<span id="cb15-18"><a href="#cb15-18"></a> gtk_expression_watch_unwatch <span class="op">(</span>watch<span class="op">);</span></span>
|
||
<span id="cb15-19"><a href="#cb15-19"></a> gtk_expression_unref <span class="op">(</span>expression<span class="op">);</span></span>
|
||
<span id="cb15-20"><a href="#cb15-20"></a> <span class="cf">return</span> false<span class="op">;</span></span>
|
||
<span id="cb15-21"><a href="#cb15-21"></a><span class="op">}</span></span>
|
||
<span id="cb15-22"><a href="#cb15-22"></a></span>
|
||
<span id="cb15-23"><a href="#cb15-23"></a><span class="dt">static</span> <span class="dt">void</span></span>
|
||
<span id="cb15-24"><a href="#cb15-24"></a>app_activate <span class="op">(</span>GApplication <span class="op">*</span>application<span class="op">)</span> <span class="op">{</span></span>
|
||
<span id="cb15-25"><a href="#cb15-25"></a> GtkApplication <span class="op">*</span>app <span class="op">=</span> GTK_APPLICATION <span class="op">(</span>application<span class="op">);</span></span>
|
||
<span id="cb15-26"><a href="#cb15-26"></a> gtk_window_present <span class="op">(</span>gtk_application_get_active_window<span class="op">(</span>app<span class="op">));</span></span>
|
||
<span id="cb15-27"><a href="#cb15-27"></a><span class="op">}</span></span>
|
||
<span id="cb15-28"><a href="#cb15-28"></a></span>
|
||
<span id="cb15-29"><a href="#cb15-29"></a><span class="dt">static</span> <span class="dt">void</span></span>
|
||
<span id="cb15-30"><a href="#cb15-30"></a>app_startup <span class="op">(</span>GApplication <span class="op">*</span>application<span class="op">)</span> <span class="op">{</span></span>
|
||
<span id="cb15-31"><a href="#cb15-31"></a> GtkApplication <span class="op">*</span>app <span class="op">=</span> GTK_APPLICATION <span class="op">(</span>application<span class="op">);</span></span>
|
||
<span id="cb15-32"><a href="#cb15-32"></a> GtkWidget <span class="op">*</span>win<span class="op">;</span></span>
|
||
<span id="cb15-33"><a href="#cb15-33"></a></span>
|
||
<span id="cb15-34"><a href="#cb15-34"></a> win <span class="op">=</span> GTK_WIDGET <span class="op">(</span>gtk_application_window_new <span class="op">(</span>app<span class="op">));</span></span>
|
||
<span id="cb15-35"><a href="#cb15-35"></a> g_signal_connect <span class="op">(</span>win<span class="op">,</span> <span class="st">"close-request"</span><span class="op">,</span> G_CALLBACK <span class="op">(</span>close_request_cb<span class="op">),</span> NULL<span class="op">);</span></span>
|
||
<span id="cb15-36"><a href="#cb15-36"></a></span>
|
||
<span id="cb15-37"><a href="#cb15-37"></a> expression <span class="op">=</span> gtk_property_expression_new <span class="op">(</span>GTK_TYPE_WINDOW<span class="op">,</span> NULL<span class="op">,</span> <span class="st">"default-width"</span><span class="op">);</span></span>
|
||
<span id="cb15-38"><a href="#cb15-38"></a> watch <span class="op">=</span> gtk_expression_watch <span class="op">(</span>expression<span class="op">,</span> win<span class="op">,</span> notify<span class="op">,</span> NULL<span class="op">,</span> NULL<span class="op">);</span></span>
|
||
<span id="cb15-39"><a href="#cb15-39"></a><span class="op">}</span></span>
|
||
<span id="cb15-40"><a href="#cb15-40"></a></span>
|
||
<span id="cb15-41"><a href="#cb15-41"></a><span class="pp">#define APPLICATION_ID "com.github.ToshioCP.exp_watch"</span></span>
|
||
<span id="cb15-42"><a href="#cb15-42"></a></span>
|
||
<span id="cb15-43"><a href="#cb15-43"></a><span class="dt">int</span></span>
|
||
<span id="cb15-44"><a href="#cb15-44"></a>main <span class="op">(</span><span class="dt">int</span> argc<span class="op">,</span> <span class="dt">char</span> <span class="op">**</span>argv<span class="op">)</span> <span class="op">{</span></span>
|
||
<span id="cb15-45"><a href="#cb15-45"></a> GtkApplication <span class="op">*</span>app<span class="op">;</span></span>
|
||
<span id="cb15-46"><a href="#cb15-46"></a> <span class="dt">int</span> stat<span class="op">;</span></span>
|
||
<span id="cb15-47"><a href="#cb15-47"></a></span>
|
||
<span id="cb15-48"><a href="#cb15-48"></a> app <span class="op">=</span> gtk_application_new <span class="op">(</span>APPLICATION_ID<span class="op">,</span> G_APPLICATION_DEFAULT_FLAGS<span class="op">);</span></span>
|
||
<span id="cb15-49"><a href="#cb15-49"></a></span>
|
||
<span id="cb15-50"><a href="#cb15-50"></a> g_signal_connect <span class="op">(</span>app<span class="op">,</span> <span class="st">"startup"</span><span class="op">,</span> G_CALLBACK <span class="op">(</span>app_startup<span class="op">),</span> NULL<span class="op">);</span></span>
|
||
<span id="cb15-51"><a href="#cb15-51"></a> g_signal_connect <span class="op">(</span>app<span class="op">,</span> <span class="st">"activate"</span><span class="op">,</span> G_CALLBACK <span class="op">(</span>app_activate<span class="op">),</span> NULL<span class="op">);</span></span>
|
||
<span id="cb15-52"><a href="#cb15-52"></a></span>
|
||
<span id="cb15-53"><a href="#cb15-53"></a> stat <span class="op">=</span>g_application_run <span class="op">(</span>G_APPLICATION <span class="op">(</span>app<span class="op">),</span> argc<span class="op">,</span> argv<span class="op">);</span></span>
|
||
<span id="cb15-54"><a href="#cb15-54"></a> g_object_unref <span class="op">(</span>app<span class="op">);</span></span>
|
||
<span id="cb15-55"><a href="#cb15-55"></a> <span class="cf">return</span> stat<span class="op">;</span></span>
|
||
<span id="cb15-56"><a href="#cb15-56"></a><span class="op">}</span></span></code></pre></div>
|
||
<ul>
|
||
<li>37: A property expression looks up the “default-width” property of
|
||
the window.</li>
|
||
<li>38: Create a watch structure for the expression. The callback
|
||
<code>notify</code> is called every time the value of the expression
|
||
changes. The ‘this’ object is <code>win</code>, so the expression
|
||
returns the default width of the window.</li>
|
||
<li>6-14: The callback function <code>notify</code>. It uses
|
||
<code>gtk_expression_watch_evaluate</code> to get the value of the
|
||
expression. The ‘this’ object is given in advance (when the watch is
|
||
created). It outputs the window width to the standard output.</li>
|
||
<li>16-21: A handler for the “close-request”signal on the window. It
|
||
stops the watch. In addition, it releases the reference to the
|
||
expression. Because <code>gtk_expression_watch</code> doesn’t take the
|
||
ownership of the expression, you own it. So, the release is
|
||
necessary.</li>
|
||
</ul>
|
||
<h2 id="gtkexpression-in-ui-files">Gtkexpression in ui files</h2>
|
||
<p>GtkBuilder supports GtkExpressions. There are four tags.</p>
|
||
<ul>
|
||
<li>constant tag to create constant expression. Type attribute specifies
|
||
the type name of the value. If no type is specified, the type is assumed
|
||
to be an object. The content is the value of the expression.</li>
|
||
<li>lookup tag to create property expression. Type attribute specifies
|
||
the type of the object. Name attribute specifies the property name. The
|
||
content is an expression or object which has the property to look up. If
|
||
there’s no content, ‘this’ object is used.</li>
|
||
<li>closure tag to create closure expression. Type attribute specifies
|
||
the type of the returned value. Function attribute specifies the
|
||
callback function. The contents of the tag are arguments that are
|
||
expressions.</li>
|
||
<li>binding tag to bind a property to an expression. It is put in the
|
||
content of an object tag. Name attribute specifies the property name of
|
||
the object. The content is an expression.</li>
|
||
</ul>
|
||
<div class="sourceCode" id="cb16"><pre
|
||
class="sourceCode xml"><code class="sourceCode xml"><span id="cb16-1"><a href="#cb16-1" aria-hidden="true" tabindex="-1"></a><<span class="kw">constant</span><span class="ot"> type=</span><span class="st">"gchararray"</span>>Hello world</<span class="kw">constant</span>></span>
|
||
<span id="cb16-2"><a href="#cb16-2" aria-hidden="true" tabindex="-1"></a><<span class="kw">lookup</span><span class="ot"> name=</span><span class="st">"label"</span><span class="ot"> type=</span><span class="st">"GtkLabel"</span>>label</<span class="kw">lookup</span>></span>
|
||
<span id="cb16-3"><a href="#cb16-3" aria-hidden="true" tabindex="-1"></a><<span class="kw">closure</span><span class="ot"> type=</span><span class="st">"gint"</span><span class="ot"> function=</span><span class="st">"callback_function"</span>></<span class="kw">closure</span>></span>
|
||
<span id="cb16-4"><a href="#cb16-4" aria-hidden="true" tabindex="-1"></a><<span class="kw">bind</span><span class="ot"> name=</span><span class="st">"label"</span>></span>
|
||
<span id="cb16-5"><a href="#cb16-5" aria-hidden="true" tabindex="-1"></a> <<span class="kw">lookup</span><span class="ot"> name=</span><span class="st">"default-width"</span>>win</<span class="kw">lookup</span>></span>
|
||
<span id="cb16-6"><a href="#cb16-6" aria-hidden="true" tabindex="-1"></a></<span class="kw">bind</span>></span></code></pre></div>
|
||
<p>These tags are usually used for GtkBuilderListItemFactory.</p>
|
||
<div class="sourceCode" id="cb17"><pre
|
||
class="sourceCode xml"><code class="sourceCode xml"><span id="cb17-1"><a href="#cb17-1" aria-hidden="true" tabindex="-1"></a><<span class="kw">interface</span>></span>
|
||
<span id="cb17-2"><a href="#cb17-2" aria-hidden="true" tabindex="-1"></a> <<span class="kw">template</span><span class="ot"> class=</span><span class="st">"GtkListItem"</span>></span>
|
||
<span id="cb17-3"><a href="#cb17-3" aria-hidden="true" tabindex="-1"></a> <<span class="kw">property</span><span class="ot"> name=</span><span class="st">"child"</span>></span>
|
||
<span id="cb17-4"><a href="#cb17-4" aria-hidden="true" tabindex="-1"></a> <<span class="kw">object</span><span class="ot"> class=</span><span class="st">"GtkLabel"</span>></span>
|
||
<span id="cb17-5"><a href="#cb17-5" aria-hidden="true" tabindex="-1"></a> <<span class="kw">binding</span><span class="ot"> name=</span><span class="st">"label"</span>></span>
|
||
<span id="cb17-6"><a href="#cb17-6" aria-hidden="true" tabindex="-1"></a> <<span class="kw">lookup</span><span class="ot"> name=</span><span class="st">"string"</span><span class="ot"> type=</span><span class="st">"GtkStringObject"</span>></span>
|
||
<span id="cb17-7"><a href="#cb17-7" aria-hidden="true" tabindex="-1"></a> <<span class="kw">lookup</span><span class="ot"> name=</span><span class="st">"item"</span>>GtkListItem</<span class="kw">lookup</span>></span>
|
||
<span id="cb17-8"><a href="#cb17-8" aria-hidden="true" tabindex="-1"></a> </<span class="kw">lookup</span>></span>
|
||
<span id="cb17-9"><a href="#cb17-9" aria-hidden="true" tabindex="-1"></a> </<span class="kw">binding</span>></span>
|
||
<span id="cb17-10"><a href="#cb17-10" aria-hidden="true" tabindex="-1"></a> </<span class="kw">object</span>></span>
|
||
<span id="cb17-11"><a href="#cb17-11" aria-hidden="true" tabindex="-1"></a> </<span class="kw">property</span>></span>
|
||
<span id="cb17-12"><a href="#cb17-12" aria-hidden="true" tabindex="-1"></a> </<span class="kw">template</span>></span>
|
||
<span id="cb17-13"><a href="#cb17-13" aria-hidden="true" tabindex="-1"></a></<span class="kw">interface</span>></span></code></pre></div>
|
||
<p>GtkBuilderListItemFactory uses GtkBuilder to extends the GtkListItem
|
||
with the XML data.</p>
|
||
<p>In the xml file above, “GtkListItem” is an instance of the
|
||
GtkListItem template. It is the ‘this’ object given to the expressions.
|
||
(The information is in the <a href="https://blog.gtk.org/2020/09/">GTK
|
||
Development Blog</a>).</p>
|
||
<p>GtkBuilder calls <code>gtk_expression_bind</code> function when it
|
||
finds a binding tag. The function sets the ‘this’ object like this:</p>
|
||
<ol type="1">
|
||
<li>If the binding tag has object attribute, the object will be the
|
||
‘this’ object.</li>
|
||
<li>If the current object of the GtkBuilder exists, it will be the
|
||
‘this’ object. That’s why a GtkListItem instance is the ‘this’ object of
|
||
the XML data for a GtkBuilderListItemFactory.</li>
|
||
<li>Otherwise, the target object of the binding tag will be the ‘this’
|
||
object.</li>
|
||
</ol>
|
||
<p>GTK 4 document doesn’t describe information about “this” object when
|
||
expressions are defined in a ui file. The information above is found
|
||
from the GTK 4 source files and it is possible to include mistakes. If
|
||
you have accurate information, please let me know.</p>
|
||
<p>A sample program <code>exp.c</code> and a ui file <code>exp.ui</code>
|
||
is in <code>src/expression</code> directory. The ui file includes
|
||
lookup, closure and bind tags. No constant tag is included. However,
|
||
constant tags are not used so often.</p>
|
||
<figure>
|
||
<img src="image/exp.png" alt="exp.c" />
|
||
<figcaption aria-hidden="true">exp.c</figcaption>
|
||
</figure>
|
||
<p>If you resize the window, the size is shown at the title of the
|
||
window. If you type characters in the entry, the same characters appear
|
||
on the label.</p>
|
||
<p>The ui file is as follows.</p>
|
||
<div class="sourceCode" id="cb18"><pre
|
||
class="sourceCode numberSource xml numberLines"><code class="sourceCode xml"><span id="cb18-1"><a href="#cb18-1"></a><span class="fu"><?xml</span><span class="ot"> version=</span><span class="st">"1.0"</span><span class="ot"> encoding=</span><span class="st">"UTF-8"</span><span class="fu">?></span></span>
|
||
<span id="cb18-2"><a href="#cb18-2"></a><<span class="kw">interface</span>></span>
|
||
<span id="cb18-3"><a href="#cb18-3"></a> <<span class="kw">object</span><span class="ot"> class=</span><span class="st">"GtkApplicationWindow"</span><span class="ot"> id=</span><span class="st">"win"</span>></span>
|
||
<span id="cb18-4"><a href="#cb18-4"></a> <<span class="kw">binding</span><span class="ot"> name=</span><span class="st">"title"</span>></span>
|
||
<span id="cb18-5"><a href="#cb18-5"></a> <<span class="kw">closure</span><span class="ot"> type=</span><span class="st">"gchararray"</span><span class="ot"> function=</span><span class="st">"set_title"</span>></span>
|
||
<span id="cb18-6"><a href="#cb18-6"></a> <<span class="kw">lookup</span><span class="ot"> name=</span><span class="st">"default-width"</span><span class="ot"> type=</span><span class="st">"GtkWindow"</span>></<span class="kw">lookup</span>></span>
|
||
<span id="cb18-7"><a href="#cb18-7"></a> <<span class="kw">lookup</span><span class="ot"> name=</span><span class="st">"default-height"</span><span class="ot"> type=</span><span class="st">"GtkWindow"</span>></<span class="kw">lookup</span>></span>
|
||
<span id="cb18-8"><a href="#cb18-8"></a> </<span class="kw">closure</span>></span>
|
||
<span id="cb18-9"><a href="#cb18-9"></a> </<span class="kw">binding</span>></span>
|
||
<span id="cb18-10"><a href="#cb18-10"></a> <<span class="kw">property</span><span class="ot"> name=</span><span class="st">"default-width"</span>>600</<span class="kw">property</span>></span>
|
||
<span id="cb18-11"><a href="#cb18-11"></a> <<span class="kw">property</span><span class="ot"> name=</span><span class="st">"default-height"</span>>400</<span class="kw">property</span>></span>
|
||
<span id="cb18-12"><a href="#cb18-12"></a> <<span class="kw">child</span>></span>
|
||
<span id="cb18-13"><a href="#cb18-13"></a> <<span class="kw">object</span><span class="ot"> class=</span><span class="st">"GtkBox"</span>></span>
|
||
<span id="cb18-14"><a href="#cb18-14"></a> <<span class="kw">property</span><span class="ot"> name=</span><span class="st">"orientation"</span>>GTK_ORIENTATION_VERTICAL</<span class="kw">property</span>></span>
|
||
<span id="cb18-15"><a href="#cb18-15"></a> <<span class="kw">child</span>></span>
|
||
<span id="cb18-16"><a href="#cb18-16"></a> <<span class="kw">object</span><span class="ot"> class=</span><span class="st">"GtkLabel"</span>></span>
|
||
<span id="cb18-17"><a href="#cb18-17"></a> <<span class="kw">binding</span><span class="ot"> name=</span><span class="st">"label"</span>></span>
|
||
<span id="cb18-18"><a href="#cb18-18"></a> <<span class="kw">lookup</span><span class="ot"> name=</span><span class="st">"text"</span>></span>
|
||
<span id="cb18-19"><a href="#cb18-19"></a> buffer</span>
|
||
<span id="cb18-20"><a href="#cb18-20"></a> </<span class="kw">lookup</span>></span>
|
||
<span id="cb18-21"><a href="#cb18-21"></a> </<span class="kw">binding</span>></span>
|
||
<span id="cb18-22"><a href="#cb18-22"></a> </<span class="kw">object</span>></span>
|
||
<span id="cb18-23"><a href="#cb18-23"></a> </<span class="kw">child</span>></span>
|
||
<span id="cb18-24"><a href="#cb18-24"></a> <<span class="kw">child</span>></span>
|
||
<span id="cb18-25"><a href="#cb18-25"></a> <<span class="kw">object</span><span class="ot"> class=</span><span class="st">"GtkEntry"</span>></span>
|
||
<span id="cb18-26"><a href="#cb18-26"></a> <<span class="kw">property</span><span class="ot"> name=</span><span class="st">"buffer"</span>></span>
|
||
<span id="cb18-27"><a href="#cb18-27"></a> <<span class="kw">object</span><span class="ot"> class=</span><span class="st">"GtkEntryBuffer"</span><span class="ot"> id=</span><span class="st">"buffer"</span>></<span class="kw">object</span>></span>
|
||
<span id="cb18-28"><a href="#cb18-28"></a> </<span class="kw">property</span>></span>
|
||
<span id="cb18-29"><a href="#cb18-29"></a> </<span class="kw">object</span>></span>
|
||
<span id="cb18-30"><a href="#cb18-30"></a> </<span class="kw">child</span>></span>
|
||
<span id="cb18-31"><a href="#cb18-31"></a> </<span class="kw">object</span>></span>
|
||
<span id="cb18-32"><a href="#cb18-32"></a> </<span class="kw">child</span>></span>
|
||
<span id="cb18-33"><a href="#cb18-33"></a> </<span class="kw">object</span>></span>
|
||
<span id="cb18-34"><a href="#cb18-34"></a></<span class="kw">interface</span>></span></code></pre></div>
|
||
<ul>
|
||
<li>4-9: The title property of the main window is bound to a closure
|
||
expression. Its callback function <code>set_title</code> is defined in
|
||
the C source file. It returns a string because the type attribute of the
|
||
tag is “gchararray”. Two parameters are given to the function. They are
|
||
width and height of the window. Lookup tags don’t have contents, so
|
||
‘this’ object is used to look up the properties. The ‘this’ object is
|
||
<code>win</code>, which is the target of the binding (<code>win</code>
|
||
includes the binding tag).</li>
|
||
<li>17-21: The “label” property of the GtkLabel instance is bound to the
|
||
“text” property of <code>buffer</code>, which is the buffer of GtkEntry
|
||
defined in line 25. If a user types characters in the entry, the same
|
||
characters appear on the label.</li>
|
||
</ul>
|
||
<p>The C source file is as follows.</p>
|
||
<div class="sourceCode" id="cb19"><pre
|
||
class="sourceCode numberSource C numberLines"><code class="sourceCode c"><span id="cb19-1"><a href="#cb19-1"></a><span class="pp">#include </span><span class="im"><gtk/gtk.h></span></span>
|
||
<span id="cb19-2"><a href="#cb19-2"></a></span>
|
||
<span id="cb19-3"><a href="#cb19-3"></a><span class="dt">char</span> <span class="op">*</span></span>
|
||
<span id="cb19-4"><a href="#cb19-4"></a>set_title <span class="op">(</span>GtkWidget <span class="op">*</span>win<span class="op">,</span> <span class="dt">int</span> width<span class="op">,</span> <span class="dt">int</span> height<span class="op">)</span> <span class="op">{</span></span>
|
||
<span id="cb19-5"><a href="#cb19-5"></a> <span class="cf">return</span> g_strdup_printf <span class="op">(</span><span class="st">"%d x %d"</span><span class="op">,</span> width<span class="op">,</span> height<span class="op">);</span></span>
|
||
<span id="cb19-6"><a href="#cb19-6"></a><span class="op">}</span></span>
|
||
<span id="cb19-7"><a href="#cb19-7"></a></span>
|
||
<span id="cb19-8"><a href="#cb19-8"></a><span class="dt">static</span> <span class="dt">void</span></span>
|
||
<span id="cb19-9"><a href="#cb19-9"></a>app_activate <span class="op">(</span>GApplication <span class="op">*</span>application<span class="op">)</span> <span class="op">{</span></span>
|
||
<span id="cb19-10"><a href="#cb19-10"></a> GtkApplication <span class="op">*</span>app <span class="op">=</span> GTK_APPLICATION <span class="op">(</span>application<span class="op">);</span></span>
|
||
<span id="cb19-11"><a href="#cb19-11"></a> gtk_window_present <span class="op">(</span>gtk_application_get_active_window<span class="op">(</span>app<span class="op">));</span></span>
|
||
<span id="cb19-12"><a href="#cb19-12"></a><span class="op">}</span></span>
|
||
<span id="cb19-13"><a href="#cb19-13"></a></span>
|
||
<span id="cb19-14"><a href="#cb19-14"></a><span class="dt">static</span> <span class="dt">void</span></span>
|
||
<span id="cb19-15"><a href="#cb19-15"></a>app_startup <span class="op">(</span>GApplication <span class="op">*</span>application<span class="op">)</span> <span class="op">{</span></span>
|
||
<span id="cb19-16"><a href="#cb19-16"></a> GtkApplication <span class="op">*</span>app <span class="op">=</span> GTK_APPLICATION <span class="op">(</span>application<span class="op">);</span></span>
|
||
<span id="cb19-17"><a href="#cb19-17"></a> GtkBuilder <span class="op">*</span>build<span class="op">;</span></span>
|
||
<span id="cb19-18"><a href="#cb19-18"></a> GtkWidget <span class="op">*</span>win<span class="op">;</span></span>
|
||
<span id="cb19-19"><a href="#cb19-19"></a></span>
|
||
<span id="cb19-20"><a href="#cb19-20"></a> build <span class="op">=</span> gtk_builder_new_from_resource <span class="op">(</span><span class="st">"/com/github/ToshioCP/exp/exp.ui"</span><span class="op">);</span></span>
|
||
<span id="cb19-21"><a href="#cb19-21"></a> win <span class="op">=</span> GTK_WIDGET <span class="op">(</span>gtk_builder_get_object <span class="op">(</span>build<span class="op">,</span> <span class="st">"win"</span><span class="op">));</span></span>
|
||
<span id="cb19-22"><a href="#cb19-22"></a> gtk_window_set_application <span class="op">(</span>GTK_WINDOW <span class="op">(</span>win<span class="op">),</span> app<span class="op">);</span></span>
|
||
<span id="cb19-23"><a href="#cb19-23"></a> g_object_unref <span class="op">(</span>build<span class="op">);</span></span>
|
||
<span id="cb19-24"><a href="#cb19-24"></a><span class="op">}</span></span>
|
||
<span id="cb19-25"><a href="#cb19-25"></a></span>
|
||
<span id="cb19-26"><a href="#cb19-26"></a><span class="pp">#define APPLICATION_ID "com.github.ToshioCP.exp"</span></span>
|
||
<span id="cb19-27"><a href="#cb19-27"></a></span>
|
||
<span id="cb19-28"><a href="#cb19-28"></a><span class="dt">int</span></span>
|
||
<span id="cb19-29"><a href="#cb19-29"></a>main <span class="op">(</span><span class="dt">int</span> argc<span class="op">,</span> <span class="dt">char</span> <span class="op">**</span>argv<span class="op">)</span> <span class="op">{</span></span>
|
||
<span id="cb19-30"><a href="#cb19-30"></a> GtkApplication <span class="op">*</span>app<span class="op">;</span></span>
|
||
<span id="cb19-31"><a href="#cb19-31"></a> <span class="dt">int</span> stat<span class="op">;</span></span>
|
||
<span id="cb19-32"><a href="#cb19-32"></a></span>
|
||
<span id="cb19-33"><a href="#cb19-33"></a> app <span class="op">=</span> gtk_application_new <span class="op">(</span>APPLICATION_ID<span class="op">,</span> G_APPLICATION_DEFAULT_FLAGS<span class="op">);</span></span>
|
||
<span id="cb19-34"><a href="#cb19-34"></a></span>
|
||
<span id="cb19-35"><a href="#cb19-35"></a> g_signal_connect <span class="op">(</span>app<span class="op">,</span> <span class="st">"startup"</span><span class="op">,</span> G_CALLBACK <span class="op">(</span>app_startup<span class="op">),</span> NULL<span class="op">);</span></span>
|
||
<span id="cb19-36"><a href="#cb19-36"></a> g_signal_connect <span class="op">(</span>app<span class="op">,</span> <span class="st">"activate"</span><span class="op">,</span> G_CALLBACK <span class="op">(</span>app_activate<span class="op">),</span> NULL<span class="op">);</span></span>
|
||
<span id="cb19-37"><a href="#cb19-37"></a></span>
|
||
<span id="cb19-38"><a href="#cb19-38"></a> stat <span class="op">=</span>g_application_run <span class="op">(</span>G_APPLICATION <span class="op">(</span>app<span class="op">),</span> argc<span class="op">,</span> argv<span class="op">);</span></span>
|
||
<span id="cb19-39"><a href="#cb19-39"></a> g_object_unref <span class="op">(</span>app<span class="op">);</span></span>
|
||
<span id="cb19-40"><a href="#cb19-40"></a> <span class="cf">return</span> stat<span class="op">;</span></span>
|
||
<span id="cb19-41"><a href="#cb19-41"></a><span class="op">}</span></span></code></pre></div>
|
||
<ul>
|
||
<li>4-6: The callback function. It returns a string (w)x(h), where the w
|
||
and h are the width and height of the window. String duplication is
|
||
necessary.</li>
|
||
</ul>
|
||
<p>The C source file is very simple because almost everything is done in
|
||
the ui file.</p>
|
||
<h2 id="conversion-between-gvalues">Conversion between GValues</h2>
|
||
<p>If you bind different type properties, type conversion is
|
||
automatically done. Suppose a label property (string) is bound to
|
||
default-width property (int).</p>
|
||
<div class="sourceCode" id="cb20"><pre
|
||
class="sourceCode xml"><code class="sourceCode xml"><span id="cb20-1"><a href="#cb20-1" aria-hidden="true" tabindex="-1"></a><<span class="kw">object</span><span class="ot"> class=</span><span class="st">"GtkLabel"</span>></span>
|
||
<span id="cb20-2"><a href="#cb20-2" aria-hidden="true" tabindex="-1"></a> <<span class="kw">binding</span><span class="ot"> name=</span><span class="st">"label"</span>></span>
|
||
<span id="cb20-3"><a href="#cb20-3" aria-hidden="true" tabindex="-1"></a> <<span class="kw">lookup</span><span class="ot"> name=</span><span class="st">"default-width"</span>></span>
|
||
<span id="cb20-4"><a href="#cb20-4" aria-hidden="true" tabindex="-1"></a> win</span>
|
||
<span id="cb20-5"><a href="#cb20-5" aria-hidden="true" tabindex="-1"></a> </<span class="kw">lookup</span>></span>
|
||
<span id="cb20-6"><a href="#cb20-6" aria-hidden="true" tabindex="-1"></a> </<span class="kw">binding</span>></span>
|
||
<span id="cb20-7"><a href="#cb20-7" aria-hidden="true" tabindex="-1"></a></<span class="kw">object</span>></span></code></pre></div>
|
||
<p>The expression created by the lookup tag returns a int type GValue.
|
||
On the other hand “label” property holds a string type GValue. When a
|
||
GValue is copied to another GValue, the type is automatically converted
|
||
if possible. If the current width is 100, an int <code>100</code> is
|
||
converted to a string <code>"100"</code>.</p>
|
||
<p>If you use <code>g_object_get</code> and <code>g_object_set</code> to
|
||
copy properties, the value is automatically converted.</p>
|
||
<h2 id="meson.build">Meson.build</h2>
|
||
<p>The source files are in <code>src/expression</code> directory. You
|
||
can build all the files at once.</p>
|
||
<pre><code>$ cd src/expression
|
||
$ meson setup _build
|
||
$ ninja -C _build</code></pre>
|
||
<p>For example, if you want to run “exp”, which is the executable file
|
||
from “exp.c”, type <code>_build/exp</code>. You can run other programs
|
||
as well.</p>
|
||
<p>The file <code>meson.build</code> is as follows.</p>
|
||
<div class="sourceCode" id="cb22"><pre
|
||
class="sourceCode numberSource numberLines"><code class="sourceCode"><span id="cb22-1"><a href="#cb22-1"></a>project('exp', 'c')</span>
|
||
<span id="cb22-2"><a href="#cb22-2"></a></span>
|
||
<span id="cb22-3"><a href="#cb22-3"></a>gtkdep = dependency('gtk4')</span>
|
||
<span id="cb22-4"><a href="#cb22-4"></a></span>
|
||
<span id="cb22-5"><a href="#cb22-5"></a>gnome=import('gnome')</span>
|
||
<span id="cb22-6"><a href="#cb22-6"></a>resources = gnome.compile_resources('resources','exp.gresource.xml')</span>
|
||
<span id="cb22-7"><a href="#cb22-7"></a></span>
|
||
<span id="cb22-8"><a href="#cb22-8"></a>sourcefiles=files('exp.c')</span>
|
||
<span id="cb22-9"><a href="#cb22-9"></a></span>
|
||
<span id="cb22-10"><a href="#cb22-10"></a>executable('exp', sourcefiles, resources, dependencies: gtkdep, export_dynamic: true, install: false)</span>
|
||
<span id="cb22-11"><a href="#cb22-11"></a>executable('exp_constant', 'exp_constant.c', dependencies: gtkdep, export_dynamic: true, install: false)</span>
|
||
<span id="cb22-12"><a href="#cb22-12"></a>executable('exp_constant_simple', 'exp_constant_simple.c', dependencies: gtkdep, export_dynamic: true, install: false)</span>
|
||
<span id="cb22-13"><a href="#cb22-13"></a>executable('exp_property_simple', 'exp_property_simple.c', dependencies: gtkdep, export_dynamic: true, install: false)</span>
|
||
<span id="cb22-14"><a href="#cb22-14"></a>executable('closure', 'closure.c', dependencies: gtkdep, export_dynamic: true, install: false)</span>
|
||
<span id="cb22-15"><a href="#cb22-15"></a>executable('closure_each', 'closure_each.c', dependencies: gtkdep, export_dynamic: true, install: false)</span>
|
||
<span id="cb22-16"><a href="#cb22-16"></a>executable('exp_closure_simple', 'exp_closure_simple.c', dependencies: gtkdep, export_dynamic: true, install: false)</span>
|
||
<span id="cb22-17"><a href="#cb22-17"></a>executable('exp_closure_with_error_report', 'exp_closure_with_error_report.c', dependencies: gtkdep, export_dynamic: true, install: false)</span>
|
||
<span id="cb22-18"><a href="#cb22-18"></a>executable('exp_bind', 'exp_bind.c', resources, dependencies: gtkdep, export_dynamic: true, install: false)</span>
|
||
<span id="cb22-19"><a href="#cb22-19"></a>executable('exp_watch', 'exp_watch.c', dependencies: gtkdep, export_dynamic: true, install: false)</span>
|
||
<span id="cb22-20"><a href="#cb22-20"></a>executable('exp_test', 'exp_test.c', resources, dependencies: gtkdep, export_dynamic: true, install: false)</span></code></pre></div>
|
||
</div>
|
||
</div>
|
||
</div>
|
||
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||
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||
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