Switch

A Switch has two positions, on and off. This example shows how you can use multiple switches together to control which Image is shown in the window. The pictures used in this example can be downloaded here.

The window will contain a "broken image" icon instead of a picture if picture files named redfox.png, muteswan.png, fruitbat.png, and gentoopenguin.png aren't in the same directory. You can change the code and the pictures around as you like, but the Creative Commons-licensed photos used in this example were taken from the following sources and cropped to 640x425:

Photo credits and licensing information are shown in the application's AboutDialog. Always remember to credit the original artist when using Creative Commons-licensed works!

Libraries to import

#!/usr/bin/gjs

const Gio = imports.gi.Gio;
const Gtk = imports.gi.Gtk;
const Lang = imports.lang;

These are the libraries we need to import for this application to run. Remember that the line which tells GNOME that we're using Gjs always needs to go at the start.

Creating the application window

const SwitchExample = new Lang.Class({
    Name: 'Switch Example',

    // Create the application itself
    _init: function() {
        this.application = new Gtk.Application({
            application_id: 'org.example.jsswitch',
            flags: Gio.ApplicationFlags.FLAGS_NONE
        });

    // Connect 'activate' and 'startup' signals to the callback functions
    this.application.connect('activate', Lang.bind(this, this._onActivate));
    this.application.connect('startup', Lang.bind(this, this._onStartup));
    },

    // Callback function for 'activate' signal presents window when active
    _onActivate: function() {
        this._window.present();
    },

    // Callback function for 'startup' signal creates the menu and builds the UI
    _onStartup: function() {
        this._initMenus();
        this._buildUI ();
    },

All the code for this sample goes in the SwitchExample class. The above code creates a Gtk.Application for our widgets and window to go in.

Before we call _buildUI to create the window and the widgets inside it, we need to call _initMenus, which tells GNOME to create the menu. We can put the actual code for _initMenus after the code for _buildUI, since it doesn't matter what order we put them in so long as _initMenus is called first in _onStartup.

    // Build the application's UI
    _buildUI: function() {

        // Create the application window
        this._window = new Gtk.ApplicationWindow({
            application: this.application,
            window_position: Gtk.WindowPosition.CENTER,
            border_width: 20,
            title: "Animal Creator"});

The _buildUI function is where we put all the code to create the application's user interface. The first step is creating a new Gtk.ApplicationWindow to put all our widgets into.

Creating the switches

        // Create the image widget and set its default picture
        this._image = new Gtk.Image ({file: "redfox.png"});

We first create the Image that the switches will control. Remember that a file named redfox.png needs to be in the same directory as this application.

        // Create a label for the first switch
        this._flyLabel = new Gtk.Label ({
            label: "Make it fly",
            margin_right: 30});

        // Create the first switch and set its default position
        this._flySwitch = new Gtk.Switch ({active: false});
        this._flySwitch.connect ('notify::active', Lang.bind (this, this._switchFlip));

        // Create a label for the second switch
        this._birdLabel = new Gtk.Label ({
            label: "Make it a bird",
            margin_right: 30});

        // Create the second switch
        this._birdSwitch = new Gtk.Switch ({active: false});
        this._birdSwitch.connect ('notify::active', Lang.bind (this, this._switchFlip));

We use a Label to mark each Switch, and give them a bit of a margin on the right so that they aren't crammed right next to the Switches. After that we create the Switches, and set them to be switched off by default.

The signal a switch sends out when it's flipped on or off is called notify::active. After we create each switch, we connect its notify::active signal to a function called _switchFlip. If you have multiple switches that each do something different, you might want to connect them to different functions, but here they're both used for the same thing: To control what picture's displayed by _image.

        // Create a grid for the labels and switches beneath the picture
        this._UIGrid = new Gtk.Grid ({
            halign: Gtk.Align.CENTER,
            valign: Gtk.Align.CENTER,
            margin_top: 20});

        // Attach the labels and switches to that grid
        this._UIGrid.attach (this._flyLabel, 0, 0, 1, 1);
        this._UIGrid.attach (this._flySwitch, 1, 0, 1, 1);
        this._UIGrid.attach (this._birdLabel, 0, 1, 1, 1);
        this._UIGrid.attach (this._birdSwitch, 1, 1, 1, 1);

        // Create a master grid to put both the UI and the picture into
        this._mainGrid = new Gtk.Grid ({
            halign: Gtk.Align.CENTER,
            valign: Gtk.Align.CENTER });

        // Attach the picture and the UI grid to the master grid
        this._mainGrid.attach (this._image, 0, 0, 1, 1);
        this._mainGrid.attach (this._UIGrid, 0, 1, 1, 1);

We create a Grid for the Labels and Switches first, so that we can organize them in a 2x2 layout with a margin between it and the Image. Then we put that Grid into a larger 2x1 Grid that has the Image on top, and the Grid with the Labels and Switches on the bottom.

        // Add the master grid to the window
        this._window.add (this._mainGrid);

        // Show the window and all child widgets
        this._window.show_all();
    },

Finally, we add the larger Grid to the window, then tell the window to show itself and all the widgets inside of it.

Function which handles the switches being flipped

    _switchFlip: function() {

        // Change the picture depending on which switches are flipped
        if (this._flySwitch.get_active()) {

            if (this._birdSwitch.get_active()) this._image.set_from_file ("muteswan.png");

            else this._image.set_from_file ("fruitbat.png");
        }

        else {

            if (this._birdSwitch.get_active()) this._image.set_from_file ("gentoopenguin.png");

            else this._image.set_from_file ("redfox.png");

        }

    },

Each time a Switch is flipped, this function checks to see which of the two Switches are active afterwards, using the Switches' built-in get_active() function. It then changes the Image accordingly. You can change the filenames around as you like, so long as you have pictures to go with them.

Creating the AboutDialog

    _initMenus: function() {

        // Build the application's menu so we can have an "About" button
        let menu = new Gio.Menu();
        menu.append("About", 'app.about');
        menu.append("Quit",'app.quit');
        this.application.set_app_menu(menu);

        // Bind the "About" button to the _showAbout() function
        let aboutAction = new Gio.SimpleAction ({ name: 'about' });
        aboutAction.connect('activate', Lang.bind(this,
            function() {
                this._showAbout();
            }));
        this.application.add_action(aboutAction);

        // Bind the "Quit" button to the function that closes the window
        let quitAction = new Gio.SimpleAction ({ name: 'quit' });
        quitAction.connect('activate', Lang.bind(this,
            function() {
                this._window.destroy();
            }));
        this.application.add_action(quitAction);
    },

The first step is building the GMenu that the "About" button goes into. This is the menu that appears when you click the application's name in the upper-left corner of the screen, next to the Activities menu. Our menu only has two options in it: About, and Quit.

    _showAbout: function () {

        // String arrays of the names of the people involved in the project
        var artists = ['Rob Lee http://en.wikipedia.org/wiki/File:Fuzzy_Freddy.jpg', 'Ken Funakoshi http://en.wikipedia.org/wiki/File:Pygoscelis_papua_-Nagasaki_Penguin_Aquarium_-swimming_underwater-8a.jpg', 'Shek Graham http://www.flickr.com/photos/shekgraham/127431519/in/photostream/', 'Mindaugas Urbonas http://commons.wikimedia.org/wiki/File:Mute_Swan-Mindaugas_Urbonas.jpg'];
        var authors = ["GNOME Documentation Team"];
        var documenters = ["GNOME Documentation Team"];

        // Create the About dialog
        let aboutDialog = new Gtk.AboutDialog({
            title: "AboutDialog Example",
            program_name: "Animal Creator",
            copyright: "Copyright \xa9 2012 GNOME Documentation Team\n\nRed fox photo licensed CC-By by Rob Lee\nGentoo penguin photo licensed CC-By-SA by Ken Funakoshi\nFruit bat photo licensed CC-By by Shek Graham\nMute swan photo licensed CC-By-SA by Mindaugas Urbonas\nLinks to the originals are available under Credits.\n\nHave you hugged a penguin today?",
            artists: artists,
            authors: authors,
            documenters: documenters,
            website: "http://developer.gnome.org",
            website_label: "GNOME Developer Website" });

        // Attach the About dialog to the window
        aboutDialog.modal = true;
        aboutDialog.transient_for = this._window;

        // Show the About dialog
        aboutDialog.show();

        // Connect the Close button to the destroy signal for the dialog
        aboutDialog.connect('response', function() {
            aboutDialog.destroy();
        });
    }

});

An AboutDialog has a lot of different things you can set, to credit everyone who worked on the application and leave a note to whomever reads it. In this case, the copyright section contains our note and credits the original photographers, while the artists section shows you a list of the photographers with links to the original photos when you click the Credits button. The web URLs put after their names in the array turn their names into clickable links in the Credits section.

// Run the application
let app = new SwitchExample ();
app.application.run (ARGV);

Finally, we create a new instance of the finished SwitchExample class, and set the application running.

Complete code sample

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#!/usr/bin/gjs

const Gio = imports.gi.Gio;
const Gtk = imports.gi.Gtk;
const Lang = imports.lang;

const SwitchExample = new Lang.Class({
    Name: 'Switch Example',

    // Create the application itself
    _init: function() {
        this.application = new Gtk.Application({
            application_id: 'org.example.jsswitch'
        });

    // Connect 'activate' and 'startup' signals to the callback functions
    this.application.connect('activate', Lang.bind(this, this._onActivate));
    this.application.connect('startup', Lang.bind(this, this._onStartup));
    },

    // Callback function for 'activate' signal presents window when active
    _onActivate: function() {
        this._window.present();
    },

    // Callback function for 'startup' signal creates the menu and builds the UI
    _onStartup: function() {
        this._initMenus();
        this._buildUI ();
    },



    // Build the application's UI
    _buildUI: function() {

        // Create the application window
        this._window = new Gtk.ApplicationWindow({
            application: this.application,
            window_position: Gtk.WindowPosition.CENTER,
            border_width: 20,
            title: "Animal Creator"});

        // Create the image widget and set its default picture
        this._image = new Gtk.Image ({file: "redfox.png"});

        // Create a label for the first switch
        this._flyLabel = new Gtk.Label ({
            label: "Make it fly",
            margin_right: 30});

        // Create the first switch and set its default position
        this._flySwitch = new Gtk.Switch ({active: false});
        this._flySwitch.connect ('notify::active', Lang.bind (this, this._switchFlip));

        // Create a label for the second switch
        this._birdLabel = new Gtk.Label ({
            label: "Make it a bird",
            margin_right: 30});

        // Create the second switch
        this._birdSwitch = new Gtk.Switch ({active: false});
        this._birdSwitch.connect ('notify::active', Lang.bind (this, this._switchFlip));

        // Create a grid for the labels and switches beneath the picture
        this._UIGrid = new Gtk.Grid ({
            halign: Gtk.Align.CENTER,
            valign: Gtk.Align.CENTER,
            margin_top: 20});

        // Attach the labels and switches to that grid
        this._UIGrid.attach (this._flyLabel, 0, 0, 1, 1);
        this._UIGrid.attach (this._flySwitch, 1, 0, 1, 1);
        this._UIGrid.attach (this._birdLabel, 0, 1, 1, 1);
        this._UIGrid.attach (this._birdSwitch, 1, 1, 1, 1);

        // Create a master grid to put both the UI and the picture into
        this._mainGrid = new Gtk.Grid ({
            halign: Gtk.Align.CENTER,
            valign: Gtk.Align.CENTER });

        // Attach the picture and the UI grid to the master grid
        this._mainGrid.attach (this._image, 0, 0, 1, 1);
        this._mainGrid.attach (this._UIGrid, 0, 1, 1, 1);

        // Add the master grid to the window
        this._window.add (this._mainGrid);

        // Show the window and all child widgets
        this._window.show_all();
    },



    _switchFlip: function() {

        // Change the picture depending on which switches are flipped
        if (this._flySwitch.get_active()) {

            if (this._birdSwitch.get_active()) this._image.set_from_file ("muteswan.png");

            else this._image.set_from_file ("fruitbat.png");
        }

        else {

            if (this._birdSwitch.get_active()) this._image.set_from_file ("gentoopenguin.png");

            else this._image.set_from_file ("redfox.png");

        }

    },



    _initMenus: function() {

        // Build the application's menu so we can have an "About" button
        let menu = new Gio.Menu();
        menu.append("About", 'app.about');
        menu.append("Quit",'app.quit');
        this.application.set_app_menu(menu);

        // Bind the "About" button to the _showAbout() function
        let aboutAction = new Gio.SimpleAction ({ name: 'about' });
        aboutAction.connect('activate', Lang.bind(this,
            function() {
                this._showAbout();
            }));
        this.application.add_action(aboutAction);

        // Bind the "Quit" button to the function that closes the window
        let quitAction = new Gio.SimpleAction ({ name: 'quit' });
        quitAction.connect('activate', Lang.bind(this,
            function() {
                this._window.destroy();
            }));
        this.application.add_action(quitAction);
    },



    _showAbout: function () {

        // String arrays of the names of the people involved in the project
        var artists = ['Rob Lee http://en.wikipedia.org/wiki/File:Fuzzy_Freddy.png', 'Ken Funakoshi http://en.wikipedia.org/wiki/File:Pygoscelis_papua_-Nagasaki_Penguin_Aquarium_-swimming_underwater-8a.png', 'Shek Graham http://www.flickr.com/photos/shekgraham/127431519/in/photostream/', 'Mindaugas Urbonas http://commons.wikimedia.org/wiki/File:Mute_Swan-Mindaugas_Urbonas.png'];
        var authors = ["GNOME Documentation Team"];
        var documenters = ["GNOME Documentation Team"];

        // Create the About dialog
        let aboutDialog = new Gtk.AboutDialog({
            title: "AboutDialog Example",
            program_name: "Animal Creator",
            copyright: "Copyright \xa9 2012 GNOME Documentation Team\n\nRed fox photo licensed CC-By by Rob Lee\nGentoo penguin photo licensed CC-By-SA by Ken Funakoshi\nFruit bat photo licensed CC-By by Shek Graham\nMute swan photo licensed CC-By-SA by Mindaugas Urbonas\nLinks to the originals are available under Credits.\n\nHave you hugged a penguin today?",
            artists: artists,
            authors: authors,
            documenters: documenters,
            website: "http://developer.gnome.org",
            website_label: "GNOME Developer Website" });

        // Attach the About dialog to the window
        aboutDialog.modal = true;
        aboutDialog.transient_for = this._window;

        // Show the About dialog
        aboutDialog.show();

        // Connect the Close button to the destroy signal for the dialog
        aboutDialog.connect('response', function() {
            aboutDialog.destroy();
        });
    }

});

// Run the application
let app = new SwitchExample ();
app.application.run (ARGV);