tfeapplication.c
includes all the code other than
tfetxtview.c
and tfenotebook.c
. It does:
The function main
is the first invoked function in C
language. It connects the command line given by the user and Gtk
application.
#define APPLICATION_ID "com.github.ToshioCP.tfe"
int
main (int argc, char **argv) {
GtkApplication *app;
int stat;
app = gtk_application_new (APPLICATION_ID, G_APPLICATION_HANDLES_OPEN);
g_signal_connect (app, "startup", G_CALLBACK (app_startup), NULL);
g_signal_connect (app, "activate", G_CALLBACK (app_activate), NULL);
g_signal_connect (app, "open", G_CALLBACK (app_open), NULL);
stat =g_application_run (G_APPLICATION (app), argc, argv);
g_object_unref (app);
return stat;
}
gtk_application_new
.Startup signal is emitted just after the GtkApplication instance is initialized. What the signal handler needs to do is the initialization of the application.
The handler is as follows.
@@@include tfe5/tfeapplication.c app_startup @@@
gtk_window_set_application
.CSS is an abbreviation of Cascading Style Sheet. It is originally used with HTML to describe the presentation semantics of a document. You might have found that the widgets in Gtk is similar to a window in a browser. It implies that CSS can also be applied to Gtk windowing system.
The syntax of CSS is as follows.
selector { color: yellow; padding-top: 10px; ...}
Every widget has CSS node. For example GtkTextView has
textview
node. If you want to set style to GtkTextView,
substitute “textview” for the selector.
textview {color: yellow; ...}
Class, ID and some other things can be applied to the selector like Web CSS. Refer to GTK 4 API Reference – CSS in Gtk for further information.
In line 30, the CSS is a string.
textview {padding: 10px; font-family: monospace; font-size: 12pt;}
GtkStyleContext is an object that stores styling information
affecting a widget. Each widget is connected to the corresponding
GtkStyleContext. You can get the context by
gtk_widget_get_style_context
.
GtkCssProvider is an object which parses CSS in order to style widgets.
To apply your CSS to widgets, you need to add GtkStyleProvider (the interface of GtkCSSProvider) to GtkStyleContext. However, instead, you can add it to GdkDisplay of the window (usually top-level window).
Look at the source file of startup
handler again.
gtk_widget_get_display
.gtk_style_context_add_provider_for_display
is the priority
of the style provider.
GTK_STYLE_PROVIDER_PRIORITY_APPLICATION
is a priority for
application-specific style information.
GTK_STYLE_PROVIDER_PRIORITY_USER
is also often used and it
is the highest priority. So,
GTK_STYLE_PROVIDER_PRIORITY_USER
is often used to a
specific widget.It is possible to add the provider to the context of GtkTextView
instead of GdkDiplay. To do so, rewrite tfe_text_view_new
.
First, get the GtkStyleContext object of a TfeTextView object. Then adds
the CSS provider to the context.
*
GtkWidget (void) {
tfe_text_view_new *tv;
GtkWidget
= gtk_widget_new (TFE_TYPE_TEXT_VIEW, NULL);
tv
*context;
GtkStyleContext
= gtk_widget_get_style_context (GTK_WIDGET (tv));
context *provider = gtk_css_provider_new ();
GtkCssProvider (provider, "textview {padding: 10px; font-family: monospace; font-size: 12pt;}", -1);
gtk_css_provider_load_from_data (context, GTK_STYLE_PROVIDER (provider), GTK_STYLE_PROVIDER_PRIORITY_USER);
gtk_style_context_add_provider
return tv;
}
CSS in the context takes precedence over CSS in the display.
@@@include tfe5/tfeapplication.c before_destroy @@@
When a widget is destroyed, or more precisely during its dispose process, a “destroy” signal is emitted. The “before_destroy” handler connects to the signal on the main window. (See the program list of app_startup.) So, it is called when the window is destroyed.
The handler removes the CSS provider from the GdkDisplay.
The handler of “activate” and “open” signal are
app_activate
and app_open
respectively. They
just create a new GtkNotebookPage.
@@@include tfe5/tfeapplication.c app_activate app_open @@@
app_activate
.app_open
.These codes have become really simple thanks to tfenotebook.c and tfetextview.c.
Only one GApplication instance can be run at a time per session. The session is a bit difficult concept and also platform-dependent, but roughly speaking, it corresponds to a graphical desktop login. When you use your PC, you probably login first, then your desktop appears until you log off. This is the session.
However, Linux is multi process OS and you can run two or more instances of the same application. Isn’t it a contradiction?
When first instance is launched, then it registers itself with its
application ID (for example, com.github.ToshioCP.tfe
). Just
after the registration, startup signal is emitted, then activate or open
signal is emitted and the instance’s main loop runs. I wrote “startup
signal is emitted just after the application instance is initialized” in
the prior subsection. More precisely, it is emitted just after the
registration.
If another instance which has the same application ID is invoked, it also tries to register itself. Because this is the second instance, the registration of the ID has already done, so it fails. Because of the failure startup signal isn’t emitted. After that, activate or open signal is emitted in the primary instance, not the second instance. The primary instance receives the signal and its handler is invoked. On the other hand, the second instance doesn’t receive the signal and it immediately quits.
Try to run two instances in a row.
$ ./_build/tfe &
[1] 84453
$ ./build/tfe tfeapplication.c
$
First, the primary instance opens a window. Then, after the second
instance is run, a new notebook page with the contents of
tfeapplication.c
appears in the primary instance’s window.
This is because the open signal is emitted in the primary instance. The
second instance immediately quits so shell prompt soon appears.
@@@include tfe5/tfeapplication.c open_cb new_cb save_cb close_cb @@@
open_cb
, new_cb
, save_cb
and
close_cb
just call corresponding notebook page
functions.
@@@include tfe5/meson.build @@@
In this file, just the source file names are modified from the prior version.
You can download the files from the repository. There are two options.
If you use git, run the terminal and type the following.
$ git clone https://github.com/ToshioCP/Gtk4-tutorial.git
The source files are under /src/tfe5 directory.