Actions

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Actions
Creating tool items, GLib.Actions, and keyboard shortcuts
GTK and GLib have a powerful API called GLib.Action which can be used to define the primary actions of your app, assign them keyboard shortcuts, and tie them to Actionable widgets in your app like Buttons and Menu Items. In this section, we're going to create a Quit action for your app with an assigned keyboard shortcut and a Button that shows that shortcut in a tooltip.
Gtk.HeaderBar
Begin by creating a Gtk.Application with a Gtk.ApplicationWindow as you've done in previous examples. Once you have that set up, let's create a new Gtk.HeaderBar. Typically your app will have a HeaderBar, at the top of the window, which will contain tool items that users will interact with to trigger your app's actions.
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protected override void activate () {
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    var header_bar = new Gtk.HeaderBar () {
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        show_close_button = true
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    };
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​
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    var main_window = new Gtk.ApplicationWindow (this) {
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        default_height = 300,
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        default_width = 300,
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        title = "Actions"
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    };
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    main_window.set_titlebar (header_bar);
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    main_window.show_all ();
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}
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Since we're using this HeaderBar as our app's main titlebar, we need to set show_close_button to true so that GTK knows to include window controls. We can then override our Window's built-in titlebar with the set_titlebar () method.
Now, still in the activate function, let's create a new Gtk.Button with a big colorful icon and add it to our headerbar:
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protected override void activate () {
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    var button = new Gtk.Button.from_icon_name ("process-stop", Gtk.IconSize.LARGE_TOOLBAR);
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​
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    var header_bar = new Gtk.HeaderBar () {
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        show_close_button = true
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    };
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    header_bar.add (button);
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​
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    [...]
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}
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elementary OS ships with a large set of system icons that you can use in your app for actions, status, and more. You can browse the full set of named icons using the app LookBook, available in AppCenter.
If you compile your app, you can see that it now has a custom HeaderBar with a big red icon in it. But when you click on it, nothing happens.
GLib.SimpleAction
Let's define a new Quit action by adding the following to the beginning of the activate () method
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var quit_action = new SimpleAction ("quit", null);
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​
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add_action (quit_action);
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set_accels_for_action ("app.quit",  {"<Control>q", "<Control>w"});
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and this to the end of the activate () method:
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quit_action.activate.connect (() => {
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    main_window.destroy ();
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});
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You'll notice that we do a few things here:
Instantiate a new GLib.SimpleAction with the name "quit"
Add the action to our Gtk.Application's ActionMap​
Set the "accelerators" (keyboard shortcuts) for "app.quit" to <Control>q and <Control>w". Notice that the action name is prefixed with app; this refers to the ActionMap built in to Gtk.Application
Connect to the activate signal of our SimpleAction and call destroy () on main_window. This must be at the end of activate () because of that reference to main_window
and now we can tie the action to the HeaderBar Button by assigning the action_name property of our Button:
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var button = new Gtk.Button.from_icon_name ("process-stop", Gtk.IconSize.LARGE_TOOLBAR) {
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    action_name = "app.quit"
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};
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Compile your app again and see that you can now quit the app either through the defined keyboard shortcuts or by clicking the Button in the HeaderBar.
Accelerator strings follow a format defined by Gtk.accelerator_parse. You can find a list of key values on Valadoc​
Granite.markup_accel_tooltip
There's one more thing we can do here to help improve your app's usability. You may have noticed that in elementary apps you can hover your pointer over tool items to see a description of the button and any available keyboard shortcuts associated with it. We can add the same thing to our Button with Granite.markup_accel_tooltip ().
First, make sure you've included Granite in the build dependencies declared in your meson.build file:
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executable(
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    meson.project_name(),
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    'src/Application.vala',
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    dependencies: [
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        dependency('granite'),
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        dependency('gtk+-3.0')
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    ],
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    install: true
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)
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Then, set the tooltip_markup property of your HeaderBar Button:
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var button = new Gtk.Button.from_icon_name ("process-stop", Gtk.IconSize.LARGE_TOOLBAR) {
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    action_name = "app.quit",
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    tooltip_markup = Granite.markup_accel_tooltip (
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        get_accels_for_action ("app.quit"),
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        "Quit"
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    )
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};
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It may now be clear why we needed to declare our action at the beginning of activate (): before we can get a list of the accelerators associated with the action, we have to define those accelerations and add them to the Application.
Compile your app one last time and hover over the HeaderBar Button to see its description and associated keyboard shortcuts.
If you're having trouble, you can view the full example code here on GitHub​
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Contents
Gtk.HeaderBar
GLib.SimpleAction
Granite.markup_accel_tooltip