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# Template XML and composite widget

The tfe program in the previous section is not so good because many things are crammed into `tfepplication.c`.
Many static variables in `tfepplication.c` shows that.

~~~C
static GtkDialog *pref;
static GtkFontButton *fontbtn;
static GSettings *settings;
static GtkDialog *alert;
static GtkLabel *lb_alert;
static GtkButton *btn_accept;

static gulong pref_close_request_handler_id = 0;
static gulong alert_close_request_handler_id = 0;
static gboolean is_quit;
~~~

Generally, if there are many global or static variables in the program, it is not a good program.
Such programs are difficult to maintain.

The file `tfeapplication.c` should be divided into several files.

- `tfeapplication.c` only has codes related to GtkApplication.
- A file for GtkApplicationWindow
- A file for a preference dialog
- A file for an alert dialog

The preference dialog is defined by a ui file.
And it has GtkBox, GtkLabel and GtkFontButton in it.
Such widget is called composite widget.
Composite widget is a child object (not child widget) of a widget.
For example, the preference composite widget is a child object of GtkDialog.
Composite widget can be built from template XML.
Next subsection shows how to build a preference dialog.

## Preference dialog

First, write a template XML file.

~~~xml
 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <interface>
 3   <template class="TfePref" parent="GtkDialog">
 4     <property name="title">Preferences</property>
 5     <property name="resizable">FALSE</property>
 6     <property name="modal">TRUE</property>
 7     <child internal-child="content_area">
 8       <object class="GtkBox" id="content_area">
 9         <child>
10           <object class="GtkBox" id="pref_boxh">
11             <property name="orientation">GTK_ORIENTATION_HORIZONTAL</property>
12             <property name="spacing">12</property>
13             <property name="margin-start">12</property>
14             <property name="margin-end">12</property>
15             <property name="margin-top">12</property>
16             <property name="margin-bottom">12</property>
17             <child>
18               <object class="GtkLabel" id="fontlabel">
19                 <property name="label">Font:</property>
20                 <property name="xalign">1</property>
21               </object>
22             </child>
23             <child>
24               <object class="GtkFontButton" id="fontbtn">
25               </object>
26             </child>
27           </object>
28         </child>
29       </object>
30     </child>
31   </template>
32 </interface>
33 
~~~

- 3: Template tag specifies a composite widget.
The value of a class attribute is the object name of the composite widget.
This XML file names the object "TfePref".
It is defined in a C source file and it will be shown later.
A parent attribute specifies the direct parent object of the composite widget.
`TfePref` is a child object of `GtkDialog`.
Therefore the value of the attribute is "GtkDialog".
A parent attribute is optional but it is recommended to specify.

Other lines are the same as before.
The object `TfePref` is defined in `tfepref.h` and `tfepref.c`.

~~~C
 1 #ifndef __TFE_PREF_H__
 2 #define __TFE_PREF_H__
 3 
 4 #include <gtk/gtk.h>
 5 
 6 #define TFE_TYPE_PREF tfe_pref_get_type ()
 7 G_DECLARE_FINAL_TYPE (TfePref, tfe_pref, TFE, PREF, GtkDialog)
 8 
 9 GtkWidget *
10 tfe_pref_new (GtkWindow *win);
11 
12 #endif /* __TFE_PREF_H__ */
13 
~~~

- 6-7: When you define a new object, you need to write these two lines.
Refer to [Section 8](sec8.md).
- 9-10: `tfe_pref_new` creates a new TfePref object.
It has a parameter `win` which is used as a transient parent window to show the dialog.

~~~C
 1 #include "tfepref.h"
 2 
 3 struct _TfePref
 4 {
 5   GtkDialog parent;
 6   GSettings *settings;
 7   GtkFontButton *fontbtn;
 8 };
 9 
10 G_DEFINE_TYPE (TfePref, tfe_pref, GTK_TYPE_DIALOG);
11 
12 static void
13 tfe_pref_dispose (GObject *gobject) {
14   TfePref *pref = TFE_PREF (gobject);
15 
16   g_clear_object (&pref->settings);
17   G_OBJECT_CLASS (tfe_pref_parent_class)->dispose (gobject);
18 }
19 
20 static void
21 tfe_pref_init (TfePref *pref) {
22   gtk_widget_init_template (GTK_WIDGET (pref));
23   pref->settings = g_settings_new ("com.github.ToshioCP.tfe");
24   g_settings_bind (pref->settings, "font", pref->fontbtn, "font", G_SETTINGS_BIND_DEFAULT);
25 }
26 
27 static void
28 tfe_pref_class_init (TfePrefClass *class) {
29   GObjectClass *object_class = G_OBJECT_CLASS (class);
30 
31   object_class->dispose = tfe_pref_dispose;
32   gtk_widget_class_set_template_from_resource (GTK_WIDGET_CLASS (class), "/com/github/ToshioCP/tfe/tfepref.ui");
33   gtk_widget_class_bind_template_child (GTK_WIDGET_CLASS (class), TfePref, fontbtn);
34 }
35 
36 GtkWidget *
37 tfe_pref_new (GtkWindow *win) {
38   return GTK_WIDGET (g_object_new (TFE_TYPE_PREF, "transient-for", win, NULL));
39 }
40 
~~~

- 3-8: The structure of an instance of this object.
It has two variables, settings and fontbtn.
- 10: `G_DEFINE_TYPE` macro.
This macro registers the TfePref type.
- 12-18: Dispose handler.
This handler is called when the instance is destroyed.
The destruction process has two stages, disposing and finalizing.
When disposing, the instance releases all the references (to the other instances).
TfePref object holds a reference to the GSettings instance.
It is released in line 16.
After that parents dispose handler is called in line 17.
For further information about destruction process, refer to [Section 11](sec11.md).
- 27-34: Class initialization function.
- 31: Set the dispose handler.
- 32: `gtk_widget_class_set_template_from_resource` function associates the description in the XML file (`tfepref.ui`) with the widget.
At this moment no instance is created.
It just make the class to know the structure of the object.
That's why the top level tag is not `<object>` but `<template>` in the XML file.
- 33: `gtk_widget_class_bind_template_child` function binds a private variable of the object with a child object in the template.
This function is a macro.
The name of the private variable (`fontbtn` in line 7) and the id `fontbtn` in the XML file (line 24) must be the same.
The pointer to the instance will be assigned to the variable `fontbtn` when the instance is created.
- 20-25: Instance initialization function.
- 22: Creates the instance based on the template in the class.
The template has been made during the class initialization process.
- 23: Create GSettings instance with the id "com.github.ToshioCP.tfe".
- 24: Bind the font key in the GSettings object to the font property in the GtkFontButton.
- 36-39: The function `tfe_pref_new` creates an instance of TfePref.
The parameter `win` is a transient parent.

Now, It is very simple to use this dialog.
A caller just creates this object and shows it.

~~~C
TfePref *pref;
pref = tfe_pref_new (win) /* win is the top-level window */
gtk_widget_show (GTK_WINDOW (win));
~~~

This instance is automatically destroyed when a user clicks on the close button.
That's all.
If you want to show the dialog again, just create and show it.

## Alert dialog

It is almost same as preference dialog.

Its XML file is:

~~~xml
 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <interface>
 3   <template class="TfeAlert" parent="GtkDialog">
 4     <property name="title">Are you sure?</property>
 5     <property name="resizable">FALSE</property>
 6     <property name="modal">TRUE</property>
 7     <child internal-child="content_area">
 8       <object class="GtkBox">
 9         <child>
10           <object class="GtkBox">
11             <property name="orientation">GTK_ORIENTATION_HORIZONTAL</property>
12             <property name="spacing">12</property>
13             <property name="margin-start">12</property>
14             <property name="margin-end">12</property>
15             <property name="margin-top">12</property>
16             <property name="margin-bottom">12</property>
17             <child>
18               <object class="GtkImage">
19                 <property name="icon-name">dialog-warning</property>
20                 <property name="icon-size">GTK_ICON_SIZE_LARGE</property>
21               </object>
22             </child>
23             <child>
24               <object class="GtkLabel" id="lb_alert">
25               </object>
26             </child>
27           </object>
28         </child>
29       </object>
30     </child>
31     <child type="action">
32       <object class="GtkButton" id="btn_cancel">
33         <property name="label">Cancel</property>
34       </object>
35     </child>
36     <child type="action">
37       <object class="GtkButton" id="btn_accept">
38         <property name="label">Close</property>
39       </object>
40     </child>
41     <action-widgets>
42       <action-widget response="cancel" default="true">btn_cancel</action-widget>
43       <action-widget response="accept">btn_accept</action-widget>
44     </action-widgets>
45   </template>
46 </interface>
47 
~~~

The header file is:

~~~C
 1 #ifndef __TFE_ALERT_H__
 2 #define __TFE_ALERT_H__
 3 
 4 #include <gtk/gtk.h>
 5 
 6 #define TFE_TYPE_ALERT tfe_alert_get_type ()
 7 G_DECLARE_FINAL_TYPE (TfeAlert, tfe_alert, TFE, ALERT, GtkDialog)
 8 
 9 void
10 tfe_alert_set_message (TfeAlert *alert, const char *message);
11 
12 void
13 tfe_alert_set_button_label (TfeAlert *alert, const char *label);
14 
15 GtkWidget *
16 tfe_alert_new (GtkWindow *win);
17 
18 #endif /* __TFE_ALERT_H__ */
19 
~~~

There are three public functions.
The functions `tfe_alert_set_message` and `tfe_alert_set_button_label` sets the label and button name of the alert dialog.
For example, if you want to show an alert that the user tries to close without saving the content, set them like:

~~~C
tfe_alert_set_message (alert, "Are you really close without saving?"); /* alert points to a TfeAlert instance */
tfe_alert_set_button_label (alert, "Close");
~~~

The function `tfe_alert_new` creates a TfeAlert dialog.

The C source file is:

~~~C
 1 #include "tfealert.h"
 2 
 3 struct _TfeAlert
 4 {
 5   GtkDialog parent;
 6   GtkLabel *lb_alert;
 7   GtkButton *btn_accept;
 8 };
 9 
10 G_DEFINE_TYPE (TfeAlert, tfe_alert, GTK_TYPE_DIALOG);
11 
12 void
13 tfe_alert_set_message (TfeAlert *alert, const char *message) {
14   gtk_label_set_text (alert->lb_alert, message);
15 }
16 
17 void
18 tfe_alert_set_button_label (TfeAlert *alert, const char *label) {
19   gtk_button_set_label (alert->btn_accept, label);
20 }
21 
22 static void
23 tfe_alert_init (TfeAlert *alert) {
24   gtk_widget_init_template (GTK_WIDGET (alert));
25 }
26 
27 static void
28 tfe_alert_class_init (TfeAlertClass *class) {
29   gtk_widget_class_set_template_from_resource (GTK_WIDGET_CLASS (class), "/com/github/ToshioCP/tfe/tfealert.ui");
30   gtk_widget_class_bind_template_child (GTK_WIDGET_CLASS (class), TfeAlert, lb_alert);
31   gtk_widget_class_bind_template_child (GTK_WIDGET_CLASS (class), TfeAlert, btn_accept);
32 }
33 
34 GtkWidget *
35 tfe_alert_new (GtkWindow *win) {
36   return GTK_WIDGET (g_object_new (TFE_TYPE_ALERT, "transient-for", win, NULL));
37 }
38 
~~~

The program is almost same as `tfepref.c`.

The instruction how to use this object is as follows.

1. Write a "response" signal handler.
2. Create a TfeAlert object.
3. Connect "response" signal to a handler
4. Show the dialog
5. In the signal handler, do something with regard to the response-id.
Then destroy the dialog.

## Top-level window

In the same way, create a child object of GtkApplicationWindow.
The object name is "TfeWindow".

~~~xml
 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <interface>
 3   <template class="TfeWindow" parent="GtkApplicationWindow">
 4     <property name="title">file editor</property>
 5     <property name="default-width">600</property>
 6     <property name="default-height">400</property>
 7     <child>
 8       <object class="GtkBox" id="boxv">
 9         <property name="orientation">GTK_ORIENTATION_VERTICAL</property>
10         <child>
11           <object class="GtkBox" id="boxh">
12             <property name="orientation">GTK_ORIENTATION_HORIZONTAL</property>
13             <child>
14               <object class="GtkLabel" id="dmy1">
15                 <property name="width-chars">10</property>
16               </object>
17             </child>
18             <child>
19               <object class="GtkButton" id="btno">
20                 <property name="label">Open</property>
21                 <property name="action-name">win.open</property>
22               </object>
23             </child>
24             <child>
25               <object class="GtkButton" id="btns">
26                 <property name="label">Save</property>
27                 <property name="action-name">win.save</property>
28               </object>
29             </child>
30             <child>
31               <object class="GtkLabel" id="dmy2">
32                 <property name="hexpand">TRUE</property>
33               </object>
34             </child>
35             <child>
36               <object class="GtkButton" id="btnc">
37                 <property name="label">Close</property>
38                 <property name="action-name">win.close</property>
39               </object>
40             </child>
41             <child>
42               <object class="GtkMenuButton" id="btnm">
43                 <property name="direction">down</property>
44                 <property name="halign">start</property>
45                 <property name="icon-name">open-menu-symbolic</property>
46               </object>
47             </child>
48             <child>
49               <object class="GtkLabel" id="dmy3">
50                 <property name="width-chars">10</property>
51               </object>
52             </child>
53           </object>
54         </child>
55         <child>
56           <object class="GtkNotebook" id="nb">
57             <property name="scrollable">TRUE</property>
58             <property name="hexpand">TRUE</property>
59             <property name="vexpand">TRUE</property>
60           </object>
61         </child>
62       </object>
63     </child>
64   </template>
65 </interface>
66 
~~~

This XML file is almost same as before except template tag and "action-name" property in buttons.

GtkButton implements GtkActionable interface, which has "action-name" property.
If this property is set, GtkButton activates the action when it is clicked.
For example, if an open button is clicked, "win.open" action will be activated and `open_activated` handler will be invoked.

This action is also used by "\<Control\>o" accelerator (See the source code of `tfewindow.c` below).
If you use "clicked" signal for the button, you need its signal handler.
Then, there are two handlers:

- a handler for the "clicked" signal on the button
- a handler for the "activate" signal on the "win.open" action, to which "\<Control\>o" accelerator is connected

These two handlers do almost same thing.
It is inefficient.
Connecting buttons to actions is a good way to reduce unnecessary codes.


~~~C
 1 #ifndef __TFE_WINDOW_H__
 2 #define __TFE_WINDOW_H__
 3 
 4 #include <gtk/gtk.h>
 5 
 6 #define TFE_TYPE_WINDOW tfe_window_get_type ()
 7 G_DECLARE_FINAL_TYPE (TfeWindow, tfe_window, TFE, WINDOW, GtkApplicationWindow)
 8 
 9 void
10 tfe_window_notebook_page_new (TfeWindow *win);
11 
12 void
13 tfe_window_notebook_page_new_with_files (TfeWindow *win, GFile **files, int n_files);
14 
15 GtkWidget *
16 tfe_window_new (GtkApplication *app);
17 
18 #endif /* __TFE_WINDOW_H__ */
19 
~~~

There are three public functions.
The function `tfe_window_notebook_page_new` creates a new notebook page.
This is a wrapper function for `notebook_page_new`.
It is called by GtkApplication object.
The function `tfe_window_notebook_page_new_with_files` creates notebook pages with a contents read from the given files.
The function `tfe_window_new` creates a TfeWindow instance.

~~~C
  1 #include "tfewindow.h"
  2 #include "tfenotebook.h"
  3 #include "tfepref.h"
  4 #include "tfealert.h"
  5 #include "css.h"
  6 
  7 struct _TfeWindow {
  8   GtkApplicationWindow parent;
  9   GtkMenuButton *btnm;
 10   GtkNotebook *nb;
 11   GSettings *settings;
 12   gboolean is_quit;
 13 };
 14 
 15 G_DEFINE_TYPE (TfeWindow, tfe_window, GTK_TYPE_APPLICATION_WINDOW);
 16 
 17 /* alert response signal handler */
 18 static void
 19 alert_response_cb (GtkDialog *alert, int response_id, gpointer user_data) {
 20   TfeWindow *win = TFE_WINDOW (user_data);
 21 
 22   if (response_id == GTK_RESPONSE_ACCEPT) {
 23     if (win->is_quit)
 24       gtk_window_destroy(GTK_WINDOW (win));
 25     else
 26       notebook_page_close (win->nb);
 27   }
 28   gtk_window_destroy (GTK_WINDOW (alert));
 29 }
 30 
 31 /* ----- action activated handlers ----- */
 32 static void
 33 open_activated (GSimpleAction *action, GVariant *parameter, gpointer user_data) {
 34   TfeWindow *win = TFE_WINDOW (user_data);
 35 
 36   notebook_page_open (GTK_NOTEBOOK (win->nb));
 37 }
 38 
 39 static void
 40 save_activated (GSimpleAction *action, GVariant *parameter, gpointer user_data) {
 41   TfeWindow *win = TFE_WINDOW (user_data);
 42 
 43   notebook_page_save (GTK_NOTEBOOK (win->nb));
 44 }
 45 
 46 static void
 47 close_activated (GSimpleAction *action, GVariant *parameter, gpointer user_data) {
 48   TfeWindow *win = TFE_WINDOW (user_data);
 49   TfeAlert *alert;
 50 
 51   if (has_saved (win->nb))
 52     notebook_page_close (win->nb);
 53   else {
 54     win->is_quit = false;
 55     alert = TFE_ALERT (tfe_alert_new (GTK_WINDOW (win)));
 56     tfe_alert_set_message (alert, "Contents aren't saved yet.\nAre you sure to close?");
 57     tfe_alert_set_button_label (alert, "Close");
 58     g_signal_connect (GTK_DIALOG (alert), "response", G_CALLBACK (alert_response_cb), win);
 59     gtk_widget_show (GTK_WIDGET (alert));
 60   }
 61 }
 62 
 63 static void
 64 new_activated (GSimpleAction *action, GVariant *parameter, gpointer user_data) {
 65   TfeWindow *win = TFE_WINDOW (user_data);
 66 
 67   notebook_page_new (GTK_NOTEBOOK (win->nb));
 68 }
 69 
 70 static void
 71 saveas_activated (GSimpleAction *action, GVariant *parameter, gpointer user_data) {
 72   TfeWindow *win = TFE_WINDOW (user_data);
 73 
 74   notebook_page_saveas (GTK_NOTEBOOK (win->nb));
 75 }
 76 
 77 static void
 78 pref_activated (GSimpleAction *action, GVariant *parameter, gpointer user_data) {
 79   TfeWindow *win = TFE_WINDOW (user_data);
 80   GtkWidget *pref;
 81 
 82   pref = tfe_pref_new (GTK_WINDOW (win));
 83   gtk_widget_show (pref);
 84 }
 85 
 86 static void
 87 quit_activated (GSimpleAction *action, GVariant *parameter, gpointer user_data) {
 88   TfeWindow *win = TFE_WINDOW (user_data);
 89 
 90   TfeAlert *alert;
 91 
 92   if (has_saved_all (GTK_NOTEBOOK (win->nb)))
 93     gtk_window_destroy (GTK_WINDOW (win));
 94   else {
 95     win->is_quit = true;
 96     alert = TFE_ALERT (tfe_alert_new (GTK_WINDOW (win)));
 97     tfe_alert_set_message (alert, "Contents aren't saved yet.\nAre you sure to quit?");
 98     tfe_alert_set_button_label (alert, "Quit");
 99     g_signal_connect (GTK_DIALOG (alert), "response", G_CALLBACK (alert_response_cb), win);
100     gtk_widget_show (GTK_WIDGET (alert));
101   }
102 }
103 
104 /* gsettings changed::font signal handler */
105 static void
106 changed_font_cb (GSettings *settings, char *key, gpointer user_data) {
107   GtkWindow *win = GTK_WINDOW (user_data); 
108   char *font;
109   PangoFontDescription *pango_font_desc;
110 
111   font = g_settings_get_string (settings, "font");
112   pango_font_desc = pango_font_description_from_string (font);
113   g_free (font);
114   set_font_for_display_with_pango_font_desc (win, pango_font_desc);
115 }
116 
117 /* --- public functions --- */
118 
119 void
120 tfe_window_notebook_page_new (TfeWindow *win) {
121   notebook_page_new (win->nb);
122 }
123 
124 void
125 tfe_window_notebook_page_new_with_files (TfeWindow *win, GFile **files, int n_files) {
126   int i;
127 
128   for (i = 0; i < n_files; i++)
129     notebook_page_new_with_file (win->nb, files[i]);
130   if (gtk_notebook_get_n_pages (win->nb) == 0)
131     notebook_page_new (win->nb);
132 }
133 
134 /* --- TfeWindow object construction/destruction --- */ 
135 static void
136 tfe_window_dispose (GObject *gobject) {
137   TfeWindow *window = TFE_WINDOW (gobject);
138 
139   g_clear_object (&window->settings);
140   G_OBJECT_CLASS (tfe_window_parent_class)->dispose (gobject);
141 }
142 
143 static void
144 tfe_window_init (TfeWindow *win) {
145   GtkBuilder *build;
146   GMenuModel *menu;
147 
148   gtk_widget_init_template (GTK_WIDGET (win));
149 
150   build = gtk_builder_new_from_resource ("/com/github/ToshioCP/tfe/menu.ui");
151   menu = G_MENU_MODEL (gtk_builder_get_object (build, "menu"));
152   gtk_menu_button_set_menu_model (win->btnm, menu);
153   g_object_unref(build);
154 
155   win->settings = g_settings_new ("com.github.ToshioCP.tfe");
156   g_signal_connect (win->settings, "changed::font", G_CALLBACK (changed_font_cb), win);
157 
158 /* ----- action ----- */
159   const GActionEntry win_entries[] = {
160     { "open", open_activated, NULL, NULL, NULL },
161     { "save", save_activated, NULL, NULL, NULL },
162     { "close", close_activated, NULL, NULL, NULL },
163     { "new", new_activated, NULL, NULL, NULL },
164     { "saveas", saveas_activated, NULL, NULL, NULL },
165     { "pref", pref_activated, NULL, NULL, NULL },
166     { "close-all", quit_activated, NULL, NULL, NULL }
167   };
168   g_action_map_add_action_entries (G_ACTION_MAP (win), win_entries, G_N_ELEMENTS (win_entries), win);
169 
170   changed_font_cb(win->settings, "font", win);
171 }
172 
173 static void
174 tfe_window_class_init (TfeWindowClass *class) {
175   GObjectClass *object_class = G_OBJECT_CLASS (class);
176 
177   object_class->dispose = tfe_window_dispose;
178   gtk_widget_class_set_template_from_resource (GTK_WIDGET_CLASS (class), "/com/github/ToshioCP/tfe/tfewindow.ui");
179   gtk_widget_class_bind_template_child (GTK_WIDGET_CLASS (class), TfeWindow, btnm);
180   gtk_widget_class_bind_template_child (GTK_WIDGET_CLASS (class), TfeWindow, nb);
181 }
182 
183 GtkWidget *
184 tfe_window_new (GtkApplication *app) {
185   return GTK_WIDGET (g_object_new (TFE_TYPE_WINDOW, "application", app, NULL));
186 }
187 
~~~

- 17-29: `alert_response_cb` is a call back function of the "response" signal of TfeAlert dialog.
This is the same as before except `gtk_window_destroy(GTK_WINDOW (win))` is used instead of `tfe_application_quit`.
- 31-102: Handlers of action activated signal.
The `user_data` is a pointer to TfeWindow instance.
- 104-115: A handler of "changed::font" signal of GSettings object.
- 111: Gets the font from GSettings data.
- 112: Gets a PangoFontDescription from the font.
In the previous version, the program gets the font description from the GtkFontButton.
The button data and GSettings data are the same.
Therefore, the data got here is the same as the data in the GtkFontButton.
In addition, we don't need to worry about the preference dialog is alive or not thanks to the GSettings.
- 114: Sets CSS on the display with the font description.
- 117-132: Public functions.
- 134-141: Dispose handler.
The GSettings object needs to be released.
- 143-171: Instance initialization function.
- 148: Creates a composite widget instance with the template.
- 151-153: Insert `menu` to the menu button.
- 155-156: Creates a GSettings instance with the id "com.github.ToshioCP.tfe".
Connects "changed::font" signal to the handler `changed_font_cb`.
This signal emits when the GSettings data is changed.
The second part "font" of the signal name "changed::font" is called details.
Signals can have details.
If a GSettings instance has more than one key, "changed" signal emits only if the key, which has the same name as the detail, changes its value.
For example, Suppose a GSettings object has three keys "a", "b" and "c".
  - "changed::a" is emitted when the value of the key "a" is changed. It isn't emitted when the value of "b" or "c" is changed.
  - "changed::b" is emitted when the value of the key "b" is changed. It isn't emitted when the value of "a" or "c" is changed.
  - "changed::c" is emitted when the value of the key "c" is changed. It isn't emitted when the value of "a" or "b" is changed.
In this version of tfe, there is only one key ("font").
So, even if the signal doesn't have a detail, the result is the same.
But in the future version, it will probably need details.
- 158-168: Creates actions.
- 170: Sets CSS font.
- 173-181: Class initialization function.
- 177: Sets the dispose handler.
- 178: Sets the composite widget template
- 179-180: Binds private variable with child objects in the template.
- 183-186: `tfe_window_new`.
This function creates TfeWindow instance.

## TfeApplication

The file `tfeapplication.c` is now very simple.

~~~C
 1 #include "tfewindow.h"
 2 
 3 /* ----- activate, open, startup handlers ----- */
 4 static void
 5 app_activate (GApplication *application) {
 6   GtkApplication *app = GTK_APPLICATION (application);
 7   GtkWidget *win = GTK_WIDGET (gtk_application_get_active_window (app));
 8 
 9   tfe_window_notebook_page_new (TFE_WINDOW (win));
10   gtk_widget_show (GTK_WIDGET (win));
11 }
12 
13 static void
14 app_open (GApplication *application, GFile ** files, gint n_files, const gchar *hint) {
15   GtkApplication *app = GTK_APPLICATION (application);
16   GtkWidget *win = GTK_WIDGET (gtk_application_get_active_window (app));
17 
18   tfe_window_notebook_page_new_with_files (TFE_WINDOW (win), files, n_files);
19   gtk_widget_show (win);
20 }
21 
22 static void
23 app_startup (GApplication *application) {
24   GtkApplication *app = GTK_APPLICATION (application);
25   int i;
26 
27   tfe_window_new (app);
28 
29 /* ----- accelerator ----- */ 
30   struct {
31     const char *action;
32     const char *accels[2];
33   } action_accels[] = {
34     { "win.open", { "<Control>o", NULL } },
35     { "win.save", { "<Control>s", NULL } },
36     { "win.close", { "<Control>w", NULL } },
37     { "win.new", { "<Control>n", NULL } },
38     { "win.saveas", { "<Shift><Control>s", NULL } },
39     { "win.close-all", { "<Control>q", NULL } },
40   };
41 
42   for (i = 0; i < G_N_ELEMENTS(action_accels); i++)
43     gtk_application_set_accels_for_action(GTK_APPLICATION(app), action_accels[i].action, action_accels[i].accels);
44 }
45 
46 /* ----- main ----- */
47 
48 #define APPLICATION_ID "com.github.ToshioCP.tfe"
49 
50 int
51 main (int argc, char **argv) {
52   GtkApplication *app;
53   int stat;
54 
55   app = gtk_application_new (APPLICATION_ID, G_APPLICATION_HANDLES_OPEN);
56 
57   g_signal_connect (app, "startup", G_CALLBACK (app_startup), NULL);
58   g_signal_connect (app, "activate", G_CALLBACK (app_activate), NULL);
59   g_signal_connect (app, "open", G_CALLBACK (app_open), NULL);
60 
61   stat =g_application_run (G_APPLICATION (app), argc, argv);
62   g_object_unref (app);
63   return stat;
64 }
65 
~~~

- 4-11: Activate signal handler.
It uses `tfe_window_notebook_page_new` instead of `notebook_page_new`.
- 13-20: Open signal handler.
Thanks to `tfe_window_notebook_page_new_with_files`, this handler becomes very simple.
- 22-44: Startup signal handler.
Most of the tasks are moved to TfeWindow, the remaining tasks are creating a window and setting accelerations.
- 48-64: A function `main`.

## Other files

Resource XML file.

~~~xml
1 <?xml version="1.0" encoding="UTF-8"?>
2 <gresources>
3   <gresource prefix="/com/github/ToshioCP/tfe">
4     <file>tfewindow.ui</file>
5     <file>tfepref.ui</file>
6     <file>tfealert.ui</file>
7     <file>menu.ui</file>
8   </gresource>
9 </gresources>
~~~

GSchema XML file

~~~xml
 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <schemalist>
 3   <schema path="/com/github/ToshioCP/tfe/" id="com.github.ToshioCP.tfe">
 4     <key name="font" type="s">
 5       <default>'Monospace 12'</default>
 6       <summary>Font</summary>
 7       <description>The font to be used for textview.</description>
 8     </key>
 9   </schema>
10 </schemalist>
~~~

Meson.build

~~~meson
 1 project('tfe', 'c')
 2 
 3 gtkdep = dependency('gtk4')
 4 
 5 gnome=import('gnome')
 6 resources = gnome.compile_resources('resources','tfe.gresource.xml')
 7 gnome.compile_schemas(build_by_default: true, depend_files: 'com.github.ToshioCP.tfe.gschema.xml')
 8 
 9 sourcefiles=files('tfeapplication.c', 'tfewindow.c', 'tfenotebook.c', 'tfepref.c', 'tfealert.c', 'css.c', '../tfetextview/tfetextview.c')
10 
11 executable('tfe', sourcefiles, resources, dependencies: gtkdep, export_dynamic: true, install: true)
12 
13 schema_dir = get_option('prefix') / get_option('datadir') / 'glib-2.0/schemas/'
14 install_data('com.github.ToshioCP.tfe.gschema.xml', install_dir: schema_dir)
15 meson.add_install_script('glib-compile-schemas', schema_dir)
16 
~~~

## Compilation and installation.

If you build Gtk4 from the source, use `--prefix` option.

~~~
$ meson --prefix=$HOME/local _build
$ ninja -C _build
$ ninja -C _build install
~~~

If you install Gtk4 from the distribution packages, you don't need the prefix option.
Maybe you need root privilege to install it.

~~~
$ meson _build
$ ninja -C _build
$ ninja -C _build install  # or 'sudo ninja -C _build install'
~~~

Source files are in [src/tfe7](../src/tfe7) directory.

We made a very small text editor.
You can add features to this editor.
When you add a new feature, care about the structure of the program.
Maybe you need to divide a file into several files like this section.
It isn't good to put many things into one file.
And it is important to think about the relationship between source files and widget structures.
It is appropriate that they correspond to each other in many cases.

Up: [Readme.md](../Readme.md),  Prev: [Section 20](sec20.md), Next: [Section 22](sec22.md)