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Define Child object
Very simple editor
We made a very simple file viewer in the previous section. Now we go on to rewrite it and make a very simple editor. Its source file name is tfe1.c (text file editor 1).
GtkTextView originally has a feature of multi line editing. Therefore, we don't need to rewrite the program from scratch. We just add two things to the file viewer.
- Static memory is needed to store a pointer to GFile.
- We need to implement file write function.
A couple of ways are possible to get memories to keep GFile.
- Use global variables.
- make a child widget object and extend the memories allocated to the widget.
Using global variables is easy to implement. Define a sufficient size array of pointers to GFile. For example,
GFile *f[20];
And f[i] corresponds to i-th GtkNotebookPage.
However, there are two problems.
One is the size of the array.
If a user gives arguments more than that, bad thing may happen.
The other is the difficulty of maintenance of the program.
It is a small program so far.
However, if you continue developing it, then its size grows bigger and bigger.
Generally speaking, the bigger the program size, the more difficult to maintain global variables.
Making child widget object is a good idea in terms of maintenance. However, one thing you need to be careful is the difference between "child object" and "child widget". What we are thinking about now is "child object". A child object includes its parent object. And a child widget object derives everything from the parent widget object.
We will define TfeTextView as a child widget object of GtkTextView. It has everything that GtkTextView has. For example, TfeTextView has GtkTextbuffer correspods to GtkTextView inside TfeTextView. And important thing is that TfeTextView can have a memory to keep a pointer to GFile.
However, to understand the general theory about gobjects is very hard especially for beginners. So, I will just show you the way how to write the code and avoid the theoretical side in the next section.
How to define a child widget of GtkTextView
Let's define TfeTextView widget object which is a child object of GtkTextView. First, look at the program below.
#define TFE_TYPE_TEXT_VIEW tfe_text_view_get_type ()
G_DECLARE_FINAL_TYPE (TfeTextView, tfe_text_view, TFE, TEXT_VIEW, GtkTextView)
struct _TfeTextView
{
GtkTextView parent;
GFile *file;
};
G_DEFINE_TYPE (TfeTextView, tfe_text_view, GTK_TYPE_TEXT_VIEW);
static void
tfe_text_view_init (TfeTextView *tv) {
}
static void
tfe_text_view_class_init (TfeTextViewClass *class) {
}
void
tfe_text_view_set_file (TfeTextView *tv, GFile *f) {
tv -> file = f;
}
GFile *
tfe_text_view_get_file (TfeTextView *tv) {
return tv -> file;
}
GtkWidget *
tfe_text_view_new (void) {
return gtk_widget_new (TFE_TYPE_TEXT_VIEW, NULL);
}
If you are curious about the background theory of this program, It's very good for you. Because to know the theory is very important for you to program GTK applications. Look at GObject API reference. All you need is described in it. However, it's a tough journey especially for beginners. For now, you don't need to know such difficult theory. Just remember the instructions below.
- TfeTextView is divided into two parts. Tfe and TextView. Tfe is called prefix, namespace or module. TextView is called object.
- There are three patterns. TfeTextView (camel case), tfe_text_view (this is used to write functions) and TFE_TEXT_VIEW (This is used to write casts).
- First, define TFE_TYPE_TEXT_VIEW as tfe_text_view_get_type (). The name is always (prefix)_TYPE_(object) and the letters are upper case. And the replacement text is always (prefix)_(object)_get_type () and the letters are lower case.
- Next, use G_DECLARE_FINAL_TYPE macro. The arguments are the child object name in camel case, lower case with underscore, prefix, object and parent object name.
- Declare the structure _TfeTextView. The underscore is necessary. The first member is the parent object. Notice this is not a pointer but the object itself. The second member and after are members of the child object. TfeTextView structure has a pointer to GFile as a member.
- Use G_DEFINE_TYPE macro. The arguments are the child object name in camel case, lower case with underscore and parent object type (prefix)_TYPE_(module).
- Define instance init function (tfe_text_view_init). Usually you don't need to do anything.
- Define class init function (tfe_text_view_class_init). You don't need to do anything in this widget.
- Write function codes you want to add (tfe_text_view_set_file and tfe_text_view_get_file).
tvis a pointer to TfeTextView object instance which is a C-struture declared with the tag _TfeTextView. So, the structure has a memberfileas a pointer to GFile.tv->file = fis an assignment offto a memberfileof the structure pointed bytv. This is an example how to use the extended memory in a child widget. - Write object generation function. Its name is (prefix)_(object)_new. If the parent object function needs parameters, this function also need them. You sometimes might want to add some parameters. It's your choice. Use gtk_widget_new function to generate the child widget. The arguments are (prefix)_TYPE_(object), a list to initialize properties and NULL. In this code no property needs to be initialized.
This program is not perfect. It has some problem. But I don't discuss it now. It will be modified later.
Close-request signal
As a first step, tfe1.c writes files just before the window closes.
GtkWindow emits "close-request" signal before it closes.
We connect the signal and the handler before_close.
A handler is a C function.
When a function is connected to a certain signal, we call the function handler.
Then, the function before_close is invoked when the signal "close-request" is emittd.
g_signal_connect (win, "close-request", G_CALLBACK (before_close), NULL);
The argument win is GtkApplicationWindow, in which the signal "close-request" is defined, and before_close is the handler.
G_CALLBACK cast is necessary before the handler.
The program of before_close is as follows.
1 static gboolean
2 before_close (GtkWindow *win, GtkWidget *nb) {
3 GtkWidget *scr;
4 GtkWidget *tv;
5 GFile *file;
6 GtkTextBuffer *tb;
7 GtkTextIter start_iter;
8 GtkTextIter end_iter;
9 gchar *contents; /* gchar is the same as char ... typedef char gchar;*/
10 guint n;
11 guint i;
12
13 n = gtk_notebook_get_n_pages (GTK_NOTEBOOK (nb));
14 for (i = 0; i < n; ++i) {
15 scr = gtk_notebook_get_nth_page (GTK_NOTEBOOK (nb), i);
16 tv = gtk_scrolled_window_get_child (GTK_SCROLLED_WINDOW (scr));
17 file = tfe_text_view_get_file (TFE_TEXT_VIEW (tv));
18 tb = gtk_text_view_get_buffer (GTK_TEXT_VIEW (tv));
19 gtk_text_buffer_get_bounds (tb, &start_iter, &end_iter);
20 contents = gtk_text_buffer_get_text (tb, &start_iter, &end_iter, FALSE);
21 if (! g_file_replace_contents (file, contents, strlen (contents), NULL, TRUE, G_FILE_CREATE_NONE, NULL, NULL, NULL))
22 g_print ("ERROR : Can't save %s.", g_file_get_path (file));
23 }
24 return FALSE;
25 }
The numbers on the left of items are line numbers in the source code.
- 13: Get the number of pages
nbhas. - 14-23: For loop with regard to the index to each pages.
- 15-17: Get GtkScrolledWindow, TfeTextView and a pointer to GFile. The pointer was stored when
on_openhandler ran. It will be shown later. - 18-20: Get GtkTextBuffer and contents. start_iter and end_iter is iterators of the buffer. I don't want to explain them now because it would take a lot of time. Just remember these lines for the present.
- 21: Write the file.
Source code of tfe1.c
Now I will show you all the source code of tfe1.c.
1 #include <gtk/gtk.h>
2
3 /* Define TfeTextView Widget which is the child object of GtkTextView */
4
5 #define TFE_TYPE_TEXT_VIEW tfe_text_view_get_type ()
6 G_DECLARE_FINAL_TYPE (TfeTextView, tfe_text_view, TFE, TEXT_VIEW, GtkTextView)
7
8 struct _TfeTextView
9 {
10 GtkTextView parent;
11 GFile *file;
12 };
13
14 G_DEFINE_TYPE (TfeTextView, tfe_text_view, GTK_TYPE_TEXT_VIEW);
15
16 static void
17 tfe_text_view_init (TfeTextView *tv) {
18 }
19
20 static void
21 tfe_text_view_class_init (TfeTextViewClass *class) {
22 }
23
24 void
25 tfe_text_view_set_file (TfeTextView *tv, GFile *f) {
26 tv -> file = f;
27 }
28
29 GFile *
30 tfe_text_view_get_file (TfeTextView *tv) {
31 return tv -> file;
32 }
33
34 GtkWidget *
35 tfe_text_view_new (void) {
36 return gtk_widget_new (TFE_TYPE_TEXT_VIEW, NULL);
37 }
38
39 /* ---------- end of the definition of TfeTextView ---------- */
40
41 static gboolean
42 before_close (GtkWindow *win, GtkWidget *nb) {
43 GtkWidget *scr;
44 GtkWidget *tv;
45 GFile *file;
46 GtkTextBuffer *tb;
47 GtkTextIter start_iter;
48 GtkTextIter end_iter;
49 gchar *contents; /* gchar is the same as char ... typedef char gchar;*/
50 guint n;
51 guint i;
52
53 n = gtk_notebook_get_n_pages (GTK_NOTEBOOK (nb));
54 for (i = 0; i < n; ++i) {
55 scr = gtk_notebook_get_nth_page (GTK_NOTEBOOK (nb), i);
56 tv = gtk_scrolled_window_get_child (GTK_SCROLLED_WINDOW (scr));
57 file = tfe_text_view_get_file (TFE_TEXT_VIEW (tv));
58 tb = gtk_text_view_get_buffer (GTK_TEXT_VIEW (tv));
59 gtk_text_buffer_get_bounds (tb, &start_iter, &end_iter);
60 contents = gtk_text_buffer_get_text (tb, &start_iter, &end_iter, FALSE);
61 if (! g_file_replace_contents (file, contents, strlen (contents), NULL, TRUE, G_FILE_CREATE_NONE, NULL, NULL, NULL))
62 g_print ("ERROR : Can't save %s.", g_file_get_path (file));
63 }
64 return FALSE;
65 }
66
67 static void
68 on_activate (GApplication *app, gpointer user_data) {
69 g_print ("You need a filename argument.\n");
70 }
71
72 static void
73 on_open (GApplication *app, GFile ** files, gint n_files, gchar *hint, gpointer user_data) {
74 GtkWidget *win;
75 GtkWidget *nb;
76 GtkWidget *lab;
77 GtkNotebookPage *nbp;
78 GtkWidget *scr;
79 GtkWidget *tv;
80 GtkTextBuffer *tb;
81 char *contents;
82 gsize length;
83 char *filename;
84 int i;
85
86 win = gtk_application_window_new (GTK_APPLICATION (app));
87 gtk_window_set_title (GTK_WINDOW (win), "file editor");
88 gtk_window_set_default_size (GTK_WINDOW (win), 400, 300);
89 gtk_window_maximize (GTK_WINDOW (win));
90
91 nb = gtk_notebook_new ();
92 gtk_window_set_child (GTK_WINDOW (win), nb);
93
94 for (i = 0; i < n_files; i++) {
95 if (g_file_load_contents (files[i], NULL, &contents, &length, NULL, NULL)) {
96 scr = gtk_scrolled_window_new ();
97 tv = tfe_text_view_new ();
98 tb = gtk_text_view_get_buffer (GTK_TEXT_VIEW (tv));
99 gtk_text_view_set_wrap_mode (GTK_TEXT_VIEW (tv), GTK_WRAP_WORD_CHAR);
100 gtk_scrolled_window_set_child (GTK_SCROLLED_WINDOW (scr), tv);
101
102 tfe_text_view_set_file (TFE_TEXT_VIEW (tv), g_file_dup (files[i]));
103 gtk_text_buffer_set_text (tb, contents, length);
104 g_free (contents);
105 filename = g_file_get_basename (files[i]);
106 lab = gtk_label_new (filename);
107 gtk_notebook_append_page (GTK_NOTEBOOK (nb), scr, lab);
108 nbp = gtk_notebook_get_page (GTK_NOTEBOOK (nb), scr);
109 g_object_set (nbp, "tab-expand", TRUE, NULL);
110 g_free (filename);
111 } else {
112 filename = g_file_get_path (files[i]);
113 g_print ("No such file: %s.\n", filename);
114 g_free (filename);
115 }
116 }
117 if (gtk_notebook_get_n_pages (GTK_NOTEBOOK (nb)) > 0) {
118 g_signal_connect (win, "close-request", G_CALLBACK (before_close), nb);
119 gtk_widget_show (win);
120 } else
121 gtk_window_destroy (GTK_WINDOW (win));
122 }
123
124 int
125 main (int argc, char **argv) {
126 GtkApplication *app;
127 int stat;
128
129 app = gtk_application_new ("com.github.ToshioCP.tfe1", G_APPLICATION_HANDLES_OPEN);
130 g_signal_connect (app, "activate", G_CALLBACK (on_activate), NULL);
131 g_signal_connect (app, "open", G_CALLBACK (on_open), NULL);
132 stat =g_application_run (G_APPLICATION (app), argc, argv);
133 g_object_unref (app);
134 return stat;
135 }
136
- 102: set the pointer to GFile into TfeTextView.
files[i]is a pointer to GFile structure. It will be freed by the system. So you need to copy it.g_file_dupduplicate the given GFile structure. - 118: connect "close-request" signal and
before_closehandler. The fourth argument is called user data and it is given to the signal handler. So,nbis given tobefore_closeas the second argument.
Now compile and run it.
Type ./a.out somefile and make sure that the file is modified.
Now we got a very simple editor. It's not smart. We need more features like open, save, saveas, change font and so on. We will add them in the next section and after. Up: Readme.md, Prev: Section 4, Next: Section 6