GTK 4 tutorial

The tfe program in the previous section is not so good because many things are crammed into tfepplication.c. And many static variables in tfepplication.c. The file tfeapplication.c should be divided into several files.

tfeapplication.c only has codes related to the application.
A file for the main window
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 can be defined as a 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. The widget is defined with template tag, not object tag.

Next subsection shows how to build a preference dialog.

Preference dialog

First, write a template XML file.

<?xml version="1.0" encoding="UTF-8"?>
<interface>
  <template class="TfePref" parent="GtkDialog">
    <property name="title">Preferences</property>
    <property name="resizable">FALSE</property>
    <property name="modal">TRUE</property>
    <child internal-child="content_area">
      <object class="GtkBox" id="content_area">
        <child>
          <object class="GtkBox" id="pref_boxh">
            <property name="orientation">GTK_ORIENTATION_HORIZONTAL</property>
            <property name="spacing">12</property>
            <property name="margin-start">12</property>
            <property name="margin-end">12</property>
            <property name="margin-top">12</property>
            <property name="margin-bottom">12</property>
            <child>
              <object class="GtkLabel" id="fontlabel">
                <property name="label">Font:</property>
                <property name="xalign">1</property>
              </object>
            </child>
            <child>
              <object class="GtkFontButton" id="fontbtn">
              </object>
            </child>
          </object>
        </child>
      </object>
    </child>
  </template>
</interface>

Template tag specifies a composite widget. The value of a class attribute is the object name. It is “TfePref”. A parent attribute specifies the direct parent class of the composite widget. Therefore. TfePref is a child class of GtkDialog. A parent attribute is optional. But it is recommended to specify it. Other lines are the same as before.

The class TfePref is defined like TfeTextView. There are two files tfepref.h and tfepref.c.

The file tfepref.h defines types and declares public functions. The definitions are public and open to any C files.

#ifndef __TFE_PREF_H__
#define __TFE_PREF_H__

#include <gtk/gtk.h>

#define TFE_TYPE_PREF tfe_pref_get_type ()
G_DECLARE_FINAL_TYPE (TfePref, tfe_pref, TFE, PREF, GtkDialog)

GtkWidget *
tfe_pref_new (void);

#endif /* __TFE_PREF_H__ */

6: Defines a type TFE_TYPE_PREF, which is a macro replaced by tfe_pref_get_type ().
7: The macro G_DECLAER_FINAL_TYPE expands to:
- The function tfe_pref_get_type () is declared.
- TfePrep type is defined as a typedef of struct _TfePrep.
- TfePrepClass type is defined as a typedef of struct {GtkDialogClass *parent;}.
- Two functions TFE_PREF () and TFE_IS_PREF () is defined.
9-10: tfe_pref_new creates a new TfePref object.

The file tfepref.c includes:

struct _TfePrep structure
G_DEFINE_TYPE macro
Initialize and dispose functions
public functions

#include <gtk/gtk.h>
#include "tfepref.h"

struct _TfePref
{
  GtkDialog parent;
  GSettings *settings;
  GtkFontButton *fontbtn;
};

G_DEFINE_TYPE (TfePref, tfe_pref, GTK_TYPE_DIALOG);

static void
tfe_pref_dispose (GObject *gobject) {
  TfePref *pref = TFE_PREF (gobject);

  g_clear_object (&pref->settings);
  G_OBJECT_CLASS (tfe_pref_parent_class)->dispose (gobject);
}

static void
tfe_pref_init (TfePref *pref) {
  gtk_widget_init_template (GTK_WIDGET (pref));
  pref->settings = g_settings_new ("com.github.ToshioCP.tfe");
  g_settings_bind (pref->settings, "font", pref->fontbtn, "font", G_SETTINGS_BIND_DEFAULT);
}

static void
tfe_pref_class_init (TfePrefClass *class) {
  GObjectClass *object_class = G_OBJECT_CLASS (class);

  object_class->dispose = tfe_pref_dispose;
  gtk_widget_class_set_template_from_resource (GTK_WIDGET_CLASS (class), "/com/github/ToshioCP/tfe/tfepref.ui");
  gtk_widget_class_bind_template_child (GTK_WIDGET_CLASS (class), TfePref, fontbtn);
}

GtkWidget *
tfe_pref_new (void) {
  return GTK_WIDGET (g_object_new (TFE_TYPE_PREF, NULL));
}

4-9: The structure struct _TfePref is defined. Every TfePref instance has its own data of the structure. The structure has references to:
- a GSettings instance
- a FontButton instance
11: G_DEFINE_TYPE macro. The macro expands to:
- the declaration of the class initialization function tfe_pref_class_init
- the declaration of the instance initialization function tfe_pref_init
- a static variable tfe_pref_parent_class that points the parent class (GtkDialogClass) structure.
- a definition of tfe_pref_get_type () function
13-19: tfe_pref_dispose function. It is called in the destruction process and releases all the reference to other objects. For further information about destruction process, refer to Section 11.
17: g_clear_object is often used in dispose handlers. g_clear_object (&pref->gsettings) does:
- g_object_unref (pref->gsettings)
- pref->settings = NULL
21-26: Instance initialization function. The argument pref points a newly created TfePref instance.
23: The function gtk_widget_init_template creates and initializes the child widgets. The widgets are created based on the template which is created in the gtk_widget_class_set_template_from_resource function.
24: Creates GSettings instance and assigns the pointer to it into pref->settings. The instance refers to a GSetting id com.github.ToshioCP.tfe.
25: Binds the GSettings data font and the font property of pref->fontbtn (GtkFontButton). The element pref->fontbtn points the GtkFontButton, which is the instance of fontbtn in the ui file. The relation was made by the gtk_widget_class_bind_template_child function.
28-35: Class initialization function.
32: Sets the dispose handler.
33: 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 makes the class recognize the structure of the object. That’s why the top level tag is not <object> but <template> in the XML file. The instance will be created in the gtk_widget_init_template function later.
34: gtk_widget_class_bind_template_child macro binds the structure member (fontbtn in struct _TfePref) and the id fontbtn in the XML file. The two names must be the same. This binding is between the member and the template (not an instance).
37-40: The function tfe_pref_new creates a TfePref instance.

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

TfePref *pref;
pref = tfe_pref_new ();
gtk_window_set_transient_for (GTK_WINDOW (pref), win); /* win is the main window */
gtk_window_present (GTK_WINDOW (pref));

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 ui file is:

<?xml version="1.0" encoding="UTF-8"?>
<interface>
  <template class="TfeAlert" parent="GtkDialog">
    <property name="title">Are you sure?</property>
    <property name="resizable">FALSE</property>
    <property name="modal">TRUE</property>
    <child internal-child="content_area">
      <object class="GtkBox">
        <child>
          <object class="GtkBox">
            <property name="orientation">GTK_ORIENTATION_HORIZONTAL</property>
            <property name="spacing">12</property>
            <property name="margin-start">12</property>
            <property name="margin-end">12</property>
            <property name="margin-top">12</property>
            <property name="margin-bottom">12</property>
            <child>
              <object class="GtkImage">
                <property name="icon-name">dialog-warning</property>
                <property name="icon-size">GTK_ICON_SIZE_LARGE</property>
              </object>
            </child>
            <child>
              <object class="GtkLabel" id="lb_alert">
              </object>
            </child>
          </object>
        </child>
      </object>
    </child>
    <child type="action">
      <object class="GtkButton" id="btn_cancel">
        <property name="label">Cancel</property>
      </object>
    </child>
    <child type="action">
      <object class="GtkButton" id="btn_accept">
        <property name="label">Close</property>
      </object>
    </child>
    <action-widgets>
      <action-widget response="cancel" default="true">btn_cancel</action-widget>
      <action-widget response="accept">btn_accept</action-widget>
    </action-widgets>
  </template>
</interface>

The header file is:

#ifndef __TFE_ALERT_H__
#define __TFE_ALERT_H__

#include <gtk/gtk.h>

#define TFE_TYPE_ALERT tfe_alert_get_type ()
G_DECLARE_FINAL_TYPE (TfeAlert, tfe_alert, TFE, ALERT, GtkDialog)

void
tfe_alert_set_message (TfeAlert *alert, const char *message);

void
tfe_alert_set_button_label (TfeAlert *alert, const char *label);

GtkWidget *
tfe_alert_new (void);

#endif /* __TFE_ALERT_H__ */

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:

tfe_alert_set_message (alert, "Contents aren't saved yet.\nAre you sure to close?");
tfe_alert_set_button_label (alert, "Close");

The function tfe_alert_new creates a TfeAlert dialog.

The C source file is:

#include <gtk/gtk.h>
#include "tfealert.h"

struct _TfeAlert
{
  GtkDialog parent;
  GtkLabel *lb_alert;
  GtkButton *btn_accept;
};

G_DEFINE_TYPE (TfeAlert, tfe_alert, GTK_TYPE_DIALOG);

void
tfe_alert_set_message (TfeAlert *alert, const char *message) {
  gtk_label_set_text (alert->lb_alert, message);
}

void
tfe_alert_set_button_label (TfeAlert *alert, const char *label) {
  gtk_button_set_label (alert->btn_accept, label);
}

static void
tfe_alert_init (TfeAlert *alert) {
  gtk_widget_init_template (GTK_WIDGET (alert));
}

static void
tfe_alert_class_init (TfeAlertClass *class) {
  gtk_widget_class_set_template_from_resource (GTK_WIDGET_CLASS (class), "/com/github/ToshioCP/tfe/tfealert.ui");
  gtk_widget_class_bind_template_child (GTK_WIDGET_CLASS (class), TfeAlert, lb_alert);
  gtk_widget_class_bind_template_child (GTK_WIDGET_CLASS (class), TfeAlert, btn_accept);
}

GtkWidget *
tfe_alert_new (void) {
  return GTK_WIDGET (g_object_new (TFE_TYPE_ALERT, NULL));
}

The program is almost same as tfepref.c.

The Usage of the alert object is as follows.

Write the “response” signal handler.
Create a TfeAlert object.
Connect “response” signal to a handler
Show the dialog
In the signal handler, do something with regard to the response-id and destroy the dialog.

Top-level window

TfeWindow is a child class of GtkApplicationWindow.

<?xml version="1.0" encoding="UTF-8"?>
<interface>
  <template class="TfeWindow" parent="GtkApplicationWindow">
    <property name="title">file editor</property>
    <property name="default-width">600</property>
    <property name="default-height">400</property>
    <child>
      <object class="GtkBox" id="boxv">
        <property name="orientation">GTK_ORIENTATION_VERTICAL</property>
        <child>
          <object class="GtkBox" id="boxh">
            <property name="orientation">GTK_ORIENTATION_HORIZONTAL</property>
            <child>
              <object class="GtkLabel" id="dmy1">
                <property name="width-chars">10</property>
              </object>
            </child>
            <child>
              <object class="GtkButton" id="btno">
                <property name="label">Open</property>
                <property name="action-name">win.open</property>
              </object>
            </child>
            <child>
              <object class="GtkButton" id="btns">
                <property name="label">Save</property>
                <property name="action-name">win.save</property>
              </object>
            </child>
            <child>
              <object class="GtkLabel" id="dmy2">
                <property name="hexpand">TRUE</property>
              </object>
            </child>
            <child>
              <object class="GtkButton" id="btnc">
                <property name="label">Close</property>
                <property name="action-name">win.close</property>
              </object>
            </child>
            <child>
              <object class="GtkMenuButton" id="btnm">
                <property name="direction">down</property>
                <property name="halign">start</property>
                <property name="icon-name">open-menu-symbolic</property>
              </object>
            </child>
            <child>
              <object class="GtkLabel" id="dmy3">
                <property name="width-chars">10</property>
              </object>
            </child>
          </object>
        </child>
        <child>
          <object class="GtkNotebook" id="nb">
            <property name="scrollable">TRUE</property>
            <property name="hexpand">TRUE</property>
            <property name="vexpand">TRUE</property>
          </object>
        </child>
      </object>
    </child>
  </template>
</interface>

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 tfeapplication.c). If you used “clicked” signal for the button, you would need its signal handler. Then, there would be 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 are almost same. It is inefficient. Connecting buttons to actions is a good way to reduce unnecessary codes.

#ifndef __TFE_WINDOW_H__
#define __TFE_WINDOW_H__

#include <gtk/gtk.h>

#define TFE_TYPE_WINDOW tfe_window_get_type ()
G_DECLARE_FINAL_TYPE (TfeWindow, tfe_window, TFE, WINDOW, GtkApplicationWindow)

void
tfe_window_notebook_page_new (TfeWindow *win);

void
tfe_window_notebook_page_new_with_files (TfeWindow *win, GFile **files, int n_files);

GtkWidget *
tfe_window_new (GtkApplication *app);

#endif /* __TFE_WINDOW_H__ */

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 TfeApplication 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.

#include <gtk/gtk.h>
#include "tfewindow.h"
#include "tfenotebook.h"
#include "tfepref.h"
#include "tfealert.h"

struct _TfeWindow {
  GtkApplicationWindow parent;
  GtkMenuButton *btnm;
  GtkNotebook *nb;
  gboolean is_quit;
};

G_DEFINE_TYPE (TfeWindow, tfe_window, GTK_TYPE_APPLICATION_WINDOW);

/* alert response signal handler */
static void
alert_response_cb (GtkDialog *alert, int response_id, gpointer user_data) {
  TfeWindow *win = TFE_WINDOW (user_data);

  gtk_window_destroy (GTK_WINDOW (alert));
  if (response_id == GTK_RESPONSE_ACCEPT) {
    if (win->is_quit)
      gtk_window_destroy(GTK_WINDOW (win));
    else
      notebook_page_close (win->nb);
  }
}

static gboolean
close_request_cb (TfeWindow *win) {
  TfeAlert *alert;

  if (has_saved_all (GTK_NOTEBOOK (win->nb)))
    return false;
  else {
    win->is_quit = true;
    alert = TFE_ALERT (tfe_alert_new ());
    gtk_window_set_transient_for (GTK_WINDOW (alert), GTK_WINDOW (win));
    tfe_alert_set_message (alert, "Contents aren't saved yet.\nAre you sure to quit?");
    tfe_alert_set_button_label (alert, "Quit");
    g_signal_connect (GTK_DIALOG (alert), "response", G_CALLBACK (alert_response_cb), win);
    gtk_window_present (GTK_WINDOW (alert));
    return true;
  }
}

/* ----- action activated handlers ----- */
static void
open_activated (GSimpleAction *action, GVariant *parameter, gpointer user_data) {
  TfeWindow *win = TFE_WINDOW (user_data);

  notebook_page_open (GTK_NOTEBOOK (win->nb));
}

static void
save_activated (GSimpleAction *action, GVariant *parameter, gpointer user_data) {
  TfeWindow *win = TFE_WINDOW (user_data);

  notebook_page_save (GTK_NOTEBOOK (win->nb));
}

static void
close_activated (GSimpleAction *action, GVariant *parameter, gpointer user_data) {
  TfeWindow *win = TFE_WINDOW (user_data);
  TfeAlert *alert;

  if (has_saved (win->nb))
    notebook_page_close (win->nb);
  else {
    win->is_quit = false;
    alert = TFE_ALERT (tfe_alert_new ());
    gtk_window_set_transient_for (GTK_WINDOW (alert), GTK_WINDOW (win));
    tfe_alert_set_message (alert, "Contents aren't saved yet.\nAre you sure to close?");
    tfe_alert_set_button_label (alert, "Close");
    g_signal_connect (GTK_DIALOG (alert), "response", G_CALLBACK (alert_response_cb), win);
    gtk_widget_show (GTK_WIDGET (alert));
  }
}

static void
new_activated (GSimpleAction *action, GVariant *parameter, gpointer user_data) {
  TfeWindow *win = TFE_WINDOW (user_data);

  notebook_page_new (GTK_NOTEBOOK (win->nb));
}

static void
saveas_activated (GSimpleAction *action, GVariant *parameter, gpointer user_data) {
  TfeWindow *win = TFE_WINDOW (user_data);

  notebook_page_saveas (GTK_NOTEBOOK (win->nb));
}

static void
pref_activated (GSimpleAction *action, GVariant *parameter, gpointer user_data) {
  TfeWindow *win = TFE_WINDOW (user_data);
  GtkWidget *pref;

  pref = tfe_pref_new ();
  gtk_window_set_transient_for (GTK_WINDOW (pref), GTK_WINDOW (win));
  gtk_window_present (GTK_WINDOW (pref));
}

static void
close_all_activated (GSimpleAction *action, GVariant *parameter, gpointer user_data) {
  TfeWindow *win = TFE_WINDOW (user_data);

  if (close_request_cb (win) == false)
    gtk_window_destroy (GTK_WINDOW (win));
}

/* --- public functions --- */

void
tfe_window_notebook_page_new (TfeWindow *win) {
  notebook_page_new (win->nb);
}

void
tfe_window_notebook_page_new_with_files (TfeWindow *win, GFile **files, int n_files) {
  int i;

  for (i = 0; i < n_files; i++)
    notebook_page_new_with_file (win->nb, files[i]);
  if (gtk_notebook_get_n_pages (win->nb) == 0)
    notebook_page_new (win->nb);
}

static void
tfe_window_init (TfeWindow *win) {
  GtkBuilder *build;
  GMenuModel *menu;

  gtk_widget_init_template (GTK_WIDGET (win));

  build = gtk_builder_new_from_resource ("/com/github/ToshioCP/tfe/menu.ui");
  menu = G_MENU_MODEL (gtk_builder_get_object (build, "menu"));
  gtk_menu_button_set_menu_model (win->btnm, menu);
  g_object_unref(build);

/* ----- action ----- */
  const GActionEntry win_entries[] = {
    { "open", open_activated, NULL, NULL, NULL },
    { "save", save_activated, NULL, NULL, NULL },
    { "close", close_activated, NULL, NULL, NULL },
    { "new", new_activated, NULL, NULL, NULL },
    { "saveas", saveas_activated, NULL, NULL, NULL },
    { "pref", pref_activated, NULL, NULL, NULL },
    { "close-all", close_all_activated, NULL, NULL, NULL }
  };
  g_action_map_add_action_entries (G_ACTION_MAP (win), win_entries, G_N_ELEMENTS (win_entries), win);

  g_signal_connect (GTK_WINDOW (win), "close-request", G_CALLBACK (close_request_cb), NULL);
}

static void
tfe_window_class_init (TfeWindowClass *class) {
  gtk_widget_class_set_template_from_resource (GTK_WIDGET_CLASS (class), "/com/github/ToshioCP/tfe/tfewindow.ui");
  gtk_widget_class_bind_template_child (GTK_WIDGET_CLASS (class), TfeWindow, btnm);
  gtk_widget_class_bind_template_child (GTK_WIDGET_CLASS (class), TfeWindow, nb);
}

GtkWidget *
tfe_window_new (GtkApplication *app) {
  return GTK_WIDGET (g_object_new (TFE_TYPE_WINDOW, "application", app, NULL));
}

7-12: _TfeWindow structure. A TfeWindow instance points the structure.
14: G_DEFINE_TYPE macro.
17-28: alert_response_cb is a call back function for the “response” signal of TfeAlert dialog.
21: Destroys the alert dialog.
22-27: If the user has clicked on the accept button, it destroys the main window or closes the current notebook page.
30-46: A “close-request” signal handler on the TfeWindow. When a user clicked on the close button (top right x-shaped button), the handler is called before the window closes. If the handler returns true, the default handler isn’t called and the window doesn’t close. If the handler returns false, the default handler is called and the window closes.
34: If has_saved_all returns true, the handler returns false and the window will close. Otherwise, it shows an alert dialog.
48-111: Handlers of action activated signal. The user_data is a pointer to the TfeWindow instance.
115-128: Public functions.
130-155: Instance initialization function.
135: The function gtk_widget_init_template creates a child widgets and initializes them.
137-140: Builds and inserts menu. It is inserted to the menu button.
143-152: Creates actions and inserts them to the window. The scope of the actions is “win”.
154: Connects the “close-request” signal and a handler.
157-162: Class initialization function.
159: Sets the composite widget template
160-161: Binds private variables with child class templates.
164-167: tfe_window_new. This function creates TfeWindow instance.

TfeApplication

The file tfeaplication.h and tfeapplication.c are now very simple. The following is the header file.

#pragma once

#include <gtk/gtk.h>

#define TFE_TYPE_APPLICATION tfe_application_get_type ()
G_DECLARE_FINAL_TYPE (TfeApplication, tfe_application, TFE, APPLICATION, GtkApplication)

TfeApplication *
tfe_application_new (const char* application_id, GApplicationFlags flags);

1: #pragma once isn’t an official pre-processor command, but widely used. It makes the header file be read only once.
5-6: TFE_TYPE_APPLICATION is defined as the type of TfeApplication. G_DECLARE_FINAL_TYPE is a macro used in the header file to define a new object.
8-9: The function tfe_application_new creates a new TfeApplication instance.

The following is tfeapplication.c. It defines the application and supports:

GSettings
CSS

#include <gtk/gtk.h>
#include "tfeapplication.h"
#include "tfewindow.h"
#include "pfd2css.h"

struct _TfeApplication {
  GtkApplication parent;
  TfeWindow *win;
  GSettings *settings;
  GtkCssProvider *provider;
};

G_DEFINE_TYPE (TfeApplication, tfe_application, GTK_TYPE_APPLICATION)

/* gsettings changed::font signal handler */
static void
changed_font_cb (GSettings *settings, char *key, gpointer user_data) {
  TfeApplication *app = TFE_APPLICATION (user_data);
  char *font, *s, *css;
  PangoFontDescription *pango_font_desc;

  font = g_settings_get_string (app->settings, "font");
  pango_font_desc = pango_font_description_from_string (font);
  g_free (font);
  s = pfd2css (pango_font_desc); // converts Pango Font Description into CSS style string
  css = g_strdup_printf ("textview {%s}", s);
  gtk_css_provider_load_from_data (app->provider, css, -1);
  g_free (s);
  g_free (css);
}

/* ----- activate, open, startup handlers ----- */
static void
app_activate (GApplication *application) {
  TfeApplication *app = TFE_APPLICATION (application);

  tfe_window_notebook_page_new (app->win);
  gtk_window_present (GTK_WINDOW (app->win));
}

static void
app_open (GApplication *application, GFile ** files, gint n_files, const gchar *hint) {
  TfeApplication *app = TFE_APPLICATION (application);

  tfe_window_notebook_page_new_with_files (app->win, files, n_files);
  gtk_window_present (GTK_WINDOW (app->win));
}

static void
app_startup (GApplication *application) {
  TfeApplication *app = TFE_APPLICATION (application);
  GtkCssProvider *provider0;
  GdkDisplay *display;
  int i;

  app->win = TFE_WINDOW (tfe_window_new (GTK_APPLICATION (app)));
  provider0 = gtk_css_provider_new ();
  gtk_css_provider_load_from_data (provider0, "textview {padding: 10px;}", -1);
  display = gdk_display_get_default ();
  gtk_style_context_add_provider_for_display (display, GTK_STYLE_PROVIDER (provider0),
                                              GTK_STYLE_PROVIDER_PRIORITY_APPLICATION);
  g_object_unref (provider0);
  app->provider = gtk_css_provider_new ();
  gtk_style_context_add_provider_for_display (display, GTK_STYLE_PROVIDER (app->provider),
                                              GTK_STYLE_PROVIDER_PRIORITY_APPLICATION);
  app->settings = g_settings_new ("com.github.ToshioCP.tfe");
  g_signal_connect (app->settings, "changed::font", G_CALLBACK (changed_font_cb), app);
  changed_font_cb(app->settings, "font", app);

/* ----- accelerator ----- */ 
  struct {
    const char *action;
    const char *accels[2];
  } action_accels[] = {
    { "win.open", { "<Control>o", NULL } },
    { "win.save", { "<Control>s", NULL } },
    { "win.close", { "<Control>w", NULL } },
    { "win.new", { "<Control>n", NULL } },
    { "win.saveas", { "<Shift><Control>s", NULL } },
    { "win.close-all", { "<Control>q", NULL } },
  };

  for (i = 0; i < G_N_ELEMENTS(action_accels); i++)
    gtk_application_set_accels_for_action(GTK_APPLICATION(app), action_accels[i].action, action_accels[i].accels);
}

static void
tfe_application_dispose (GObject *gobject) {
  TfeApplication *app = TFE_APPLICATION (gobject);

  g_clear_object (&app->settings);
  g_clear_object (&app->provider);
  G_OBJECT_CLASS (tfe_application_parent_class)->dispose (gobject);
}

static void
tfe_application_init (TfeApplication *app) {
  g_signal_connect (G_APPLICATION (app), "startup", G_CALLBACK (app_startup), NULL);
  g_signal_connect (G_APPLICATION (app), "activate", G_CALLBACK (app_activate), NULL);
  g_signal_connect (G_APPLICATION (app), "open", G_CALLBACK (app_open), NULL);
}

static void
tfe_application_class_init (TfeApplicationClass *class) {
  GObjectClass *object_class = G_OBJECT_CLASS (class);

  object_class->dispose = tfe_application_dispose;
}

TfeApplication *
tfe_application_new (const char* application_id, GApplicationFlags flags) {
  return TFE_APPLICATION (g_object_new (TFE_TYPE_APPLICATION, "application-id", application_id, "flags", flags, NULL));
}

6-11: Defines _TfeApplication structure. The members are:
- win: main window instance
- settings: GSettings instance.it is bound to “font” item in the GSettings
- provider: a provider for the font of the textview.
G_DEFINE_TYPE macro.
16-30: changed_font_cb is a handler for “changed::font” signal on the GSettings instance. The signal name is “changed” and “font” is a key name. When the valeu of “font” key is changed, the signal is emitted. So, this handler doesn’t directly relate to the font button, but through the GSettings database. A user changes the font in the font button => GSettings font key data is changed => the handler is called.
22-24: Retrieves a string from the GSetting database and converts it into a pango font description.
25-29: Sets the css provider with the font data. The provider has been inserted to the current display in advance.
33-39: Activate signal handler. It uses tfe_window_notebook_page_new instead of notebook_page_new.
41-47: Open signal handler. It just calls tfe_window_notebook_page_new_with_files and shows the main window. Be careful that the activate and open handlers don’t create a new window. They just create a new notebook page. Therefore, even if the second application runs, no new window appears. Just a new notebook page is inserted to the same main window.
49-85: Startup signal handler.
56: Creates a new window (main window) and assigns it to app->win.
57-61: Creates a css provider (provider0). It includes only the padding data for the textview. The provider is inserted to the default display.
63-65: Another css provider is created (app->provider) and inserted to the default display. It will include the font data for the textview.
66-68: Creates a new GSettings instance. If the GSettings data is changed, the “changed” signal is emitted. The signal can have a key name like “changed::font”. This style (“changed::font”) is called detailed signal. The detailed signal is emitted only if the font data is changed. The handler changed_font_cb is called to set the CSS with the font data. The handler gets the font data from the GSettings data which is the last font in the previous run of the application.
71-84: Defines accelerators.
87-94: A dispose handler. It releases references to the instances of GSettings and GtkCssProvider.
96-101: An initialization for the instance. It connects three signals (activate, open and startup) and their handlers.
183-188: An initialization for the class. It overrides the dispose class method.
110-113: tfe_application_new creates a new TfeApplication instance. The parameters are an application-id and flags.

Other files

main.c

#include <gtk/gtk.h>
#include "tfeapplication.h"

#define APPLICATION_ID "com.github.ToshioCP.tfe"

int
main (int argc, char **argv) {
  TfeApplication *app;
  int stat;

  app = tfe_application_new (APPLICATION_ID, G_APPLICATION_HANDLES_OPEN);
  stat =g_application_run (G_APPLICATION (app), argc, argv);
  g_object_unref (app);
  return stat;
}

CSS related files pfd2css.h and pfd2css.c are the same as the previous section.

Resource XML file.

<?xml version="1.0" encoding="UTF-8"?>
<gresources>
  <gresource prefix="/com/github/ToshioCP/tfe">
    <file>tfewindow.ui</file>
    <file>tfepref.ui</file>
    <file>tfealert.ui</file>
    <file>menu.ui</file>
  </gresource>
</gresources>

GSchema XML file

<?xml version="1.0" encoding="UTF-8"?>
<schemalist>
  <schema path="/com/github/ToshioCP/tfe/" id="com.github.ToshioCP.tfe">
    <key name="font" type="s">
      <default>'Monospace 12'</default>
      <summary>Font</summary>
      <description>A font to be used for textview.</description>
    </key>
  </schema>
</schemalist>

Meson.build

project('tfe', 'c')

gtkdep = dependency('gtk4')

gnome=import('gnome')
resources = gnome.compile_resources('resources','tfe.gresource.xml')
gnome.compile_schemas(build_by_default: true, depend_files: 'com.github.ToshioCP.tfe.gschema.xml')

sourcefiles=files('main.c', 'tfeapplication.c', 'tfewindow.c', 'tfenotebook.c', 'tfepref.c', 'tfealert.c', 'pfd2css.c', '../tfetextview/tfetextview.c')

executable('tfe', sourcefiles, resources, dependencies: gtkdep, export_dynamic: true, install: true)

schema_dir = get_option('prefix') / get_option('datadir') / 'glib-2.0/schemas/'
install_data('com.github.ToshioCP.tfe.gschema.xml', install_dir: schema_dir)
gnome.post_install (glib_compile_schemas: true)

Compilation and installation.

If you want to install it to your local area, use --prefix=$HOME/.local or --prefix=$HOME option. If you want to install it to the system area, no option is needed. It will be installed under /user/local directory.

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

You need root privilege to install it to the system area..

$ meson _build
$ ninja -C _build
$ sudo ninja -C _build install

Source files are in src/tfe7 directory.

Composite widgets give us two advantages.

A set of widgets is better than individual widgets because of the simple coding.
They hold instance variables (members of the object structure) so static variables are no longer necessary. It makes the program simpler.