21. Application

Gtk.Application encompeses many repetitive tasks that a modern application needs such as handling multiple instances, D-Bus activation, opening files, command line parsing, startup/shutdown, menu management, window management, and more.

21.1. Actions

Gio.Action is a way to expose any single task your application or widget does by a name. These actions can be disabled/enabled at runtime and they can either be activated or have a state changed (if they contain state).

The reason to use actions is to separate out the logic from the UI. For example this allows using a menubar on OSX and a gear menu on GNOME both simply referencing the name of an action. The main implementation of this you will be using is Gio.SimpleAction which will be showed off later.

Many classes such as Gio.MenuItem and Gtk.ModelButton support properties to set an action name.

These actions can be grouped together into a Gio.ActionGroup and when these groups are added to a widget with Gtk.Widget.insert_action_group() they will gain a prefix. Such as “win” when added to a Gtk.ApplicationWindow. You will use the full action name when referencing it such as “app.about” but when you create the action it will just be “about” until added to the application.

You can also very easily make keybindings for actions by setting the accel property in the Gio.Menu file or by using Gtk.Application.add_accelerator().

21.3. Command Line

When creating your application it takes a flag property of Gio.ApplicationFlags. Using this you can let it handle everything itself or have more custom behavior.

You can use HANDLES_COMMAND_LINE to allow custom behavior in Gio.Application.do_command_line(). In combination with Gio.Application.add_main_option() to add custom options.

Using HANDLES_OPEN will do the work of simply taking file arguments for you and let you handle it in Gio.Application.do_open().

If your application is already open these will all be sent to the existing instance unless you use NON_UNIQUE to allow multiple instances.

21.4. Example

_images/application_example.png
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import sys

import gi
gi.require_version('Gtk', '3.0')
from gi.repository import GLib, Gio, Gtk

# This would typically be its own file
MENU_XML="""
<?xml version="1.0" encoding="UTF-8"?>
<interface>
  <menu id="app-menu">
    <section>
      <attribute name="label" translatable="yes">Change label</attribute>
      <item>
        <attribute name="action">win.change_label</attribute>
        <attribute name="target">String 1</attribute>
        <attribute name="label" translatable="yes">String 1</attribute>
      </item>
      <item>
        <attribute name="action">win.change_label</attribute>
        <attribute name="target">String 2</attribute>
        <attribute name="label" translatable="yes">String 2</attribute>
      </item>
      <item>
        <attribute name="action">win.change_label</attribute>
        <attribute name="target">String 3</attribute>
        <attribute name="label" translatable="yes">String 3</attribute>
      </item>
    </section>
    <section>
      <item>
        <attribute name="action">win.maximize</attribute>
        <attribute name="label" translatable="yes">Maximize</attribute>
      </item>
    </section>
    <section>
      <item>
        <attribute name="action">app.about</attribute>
        <attribute name="label" translatable="yes">_About</attribute>
      </item>
      <item>
        <attribute name="action">app.quit</attribute>
        <attribute name="label" translatable="yes">_Quit</attribute>
        <attribute name="accel">&lt;Primary&gt;q</attribute>
    </item>
    </section>
  </menu>
</interface>
"""

class AppWindow(Gtk.ApplicationWindow):

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

        # This will be in the windows group and have the "win" prefix
        max_action = Gio.SimpleAction.new_stateful("maximize", None,
                                           GLib.Variant.new_boolean(False))
        max_action.connect("change-state", self.on_maximize_toggle)
        self.add_action(max_action)

        # Keep it in sync with the actual state
        self.connect("notify::is-maximized",
                            lambda obj, pspec: max_action.set_state(
                                               GLib.Variant.new_boolean(obj.props.is_maximized)))

        lbl_variant = GLib.Variant.new_string("String 1")
        lbl_action = Gio.SimpleAction.new_stateful("change_label", lbl_variant.get_type(),
                                               lbl_variant)
        lbl_action.connect("change-state", self.on_change_label_state)
        self.add_action(lbl_action)

        self.label = Gtk.Label(label=lbl_variant.get_string(),
                               margin=30)
        self.add(self.label)
        self.label.show()

    def on_change_label_state(self, action, value):
        action.set_state(value)
        self.label.set_text(value.get_string())

    def on_maximize_toggle(self, action, value):
        action.set_state(value)
        if value.get_boolean():
            self.maximize()
        else:
            self.unmaximize()

class Application(Gtk.Application):

    def __init__(self, *args, **kwargs):
        super().__init__(*args, application_id="org.example.myapp",
                         flags=Gio.ApplicationFlags.HANDLES_COMMAND_LINE,
                         **kwargs)
        self.window = None

        self.add_main_option("test", ord("t"), GLib.OptionFlags.NONE,
                             GLib.OptionArg.NONE, "Command line test", None)

    def do_startup(self):
        Gtk.Application.do_startup(self)

        action = Gio.SimpleAction.new("about", None)
        action.connect("activate", self.on_about)
        self.add_action(action)

        action = Gio.SimpleAction.new("quit", None)
        action.connect("activate", self.on_quit)
        self.add_action(action)

        builder = Gtk.Builder.new_from_string(MENU_XML, -1)
        self.set_app_menu(builder.get_object("app-menu"))

    def do_activate(self):
        # We only allow a single window and raise any existing ones
        if not self.window:
            # Windows are associated with the application
            # when the last one is closed the application shuts down
            self.window = AppWindow(application=self, title="Main Window")

        self.window.present()

    def do_command_line(self, command_line):
        options = command_line.get_options_dict()

        if options.contains("test"):
            # This is printed on the main instance
            print("Test argument recieved")

        self.activate()
        return 0

    def on_about(self, action, param):
        about_dialog = Gtk.AboutDialog(transient_for=self.window, modal=True)
        about_dialog.present()

    def on_quit(self, action, param):
        self.quit()

if __name__ == "__main__":
    app = Application()
    app.run(sys.argv)