# MessageDialog (JavaScript)

Taryn Fox
jewelfox@fursona.net 2012
A popup message attached to a window

# MessageDialog

A MessageDialog is a modal message dialog, which means a popup that you have to respond to before you get back to what you were doing in the window that it's attached to. This one can cause the world to explode (or at least it says that it can). To make the popup appear when you run this sample, click on "Message" inside of its application menu -- that's the menu that appears when you click on an application's name in the upper-left screen corner, next to Activities.

The difference between a MessageDialog and a Dialog is that a Dialog can contain whatever widgets and content you want to put in it, whereas a MessageDialog is just a convenient way to make popups appear with a basic message and buttons.

# 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 MessageDialogExample = new Lang.Class ({ Name: 'MessageDialog Example',

// Create the application itself _init: function () { this.application = new Gtk.Application ({ application_id: 'org.example.jsmessagedialog', 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 windows when active _onActivate: function () { this._window.present (); },

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

All the code for this sample goes in the MessageDialogExample 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, title: "Gtk.MessageDialog Example", default_height: 200, default_width: 400 });

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.

// Create a silly warning message and add it to the window this.warningLabel = new Gtk.Label ({ label: "This application goes boom! (Not really.)"}); this._window.add (this.warningLabel);

For this example, all that we have in the window the popup comes out of is a silly warning Label.

# Creating the application's menu

// Build the application menu, including the button that calls the dialog _initMenus: function() { let menu = new Gio.Menu(); menu.append("Message",'app.message'); menu.append("Quit",'app.quit'); this.application.set_app_menu(menu);

// This pops up a MessageDialog when "Message" is clicked in the menu let messageAction = new Gio.SimpleAction ({ name: 'message' }); messageAction.connect('activate', Lang.bind(this, function() { this._showMessageDialog(); })); this.application.add_action(messageAction);

// This closes the window when "Quit" is clicked in the menu let quitAction = new Gio.SimpleAction ({ name: 'quit' }); quitAction.connect('activate', Lang.bind(this, function() { this._window.destroy(); })); this.application.add_action(quitAction); },

Here, we build the GMenu where we'll be putting the "Message" button which triggers the popup MessageDialog. The GMenu 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: Message, and Quit.

# Creating the MessageDialog

_showMessageDialog: function () {

// Create a modal MessageDialog whose parent is the window this._messageDialog = new Gtk.MessageDialog ({ transient_for: this._window, modal: true, buttons: Gtk.ButtonsType.OK_CANCEL, message_type: Gtk.MessageType.WARNING, text: "This action will cause the universe to stop existing." });

this._messageDialog.connect ('response', Lang.bind(this, this._response_cb)); this._messageDialog.show(); },

To make our MessageDialog a popup attached to the main window, we set its modal property to true and set it to be "transient_for" _window. After that, we can set what kind of buttons it has and what kind of message it is (which determines what icon appears next to the message), and write out the text inside it, before connecting its "response" signal to the callback function which handles it.

Here are some resources for making your own MessageDialogs:

List of button types

List of message types

// Callback function (aka signal handler) for the response signal _response_cb: function (messagedialog, response_id) {

// A simple switch that changes the main window's label switch (response_id) { case Gtk.ResponseType.OK: this.warningLabel.set_label ("*BOOM*\n"); break; case Gtk.ResponseType.CANCEL: this.warningLabel.set_label ("Good choice!\n"); break; case Gtk.ResponseType.DELETE_EVENT: this.warningLabel.set_label ("Dialog closed or cancelled.\n"); break; }

this._messageDialog.destroy();

}

});

This function takes two parameters, the MessageDialog and its response_id, both of which are automatically supplied (you don't have to manually pass them to it for it to work). Here we use a simple switch to change the "warning label"'s text, depending on which option you select. The DELETE_EVENT occurs if you press Escape to cancel the MessageDialog, instead of clicking OK or Cancel. Whatever you select, the popup is destroyed afterwards.

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

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

# Complete code sample

#!/usr/bin/gjs

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

const MessageDialogExample = new Lang.Class ({ Name: 'MessageDialog Example',

// Create the application itself _init: function () { this.application = new Gtk.Application ({ application_id: 'org.example.jsmessagedialog', 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 windows when active _onActivate: function () { this._window.present (); },

// Callback function for 'startup' signal initializes menus 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, title: "Gtk.MessageDialog Example", default_height: 200, default_width: 400 });

// Create a silly warning message and add it to the window this.warningLabel = new Gtk.Label ({ label: "This application goes boom! (Not really.)"}); this._window.add (this.warningLabel);

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

// Build the application menu, including the button that calls the dialog _initMenus: function() { let menu = new Gio.Menu(); menu.append("Message",'app.message'); menu.append("Quit",'app.quit'); this.application.set_app_menu(menu);

// This pops up a MessageDialog when "Message" is clicked in the menu let messageAction = new Gio.SimpleAction ({ name: 'message' }); messageAction.connect('activate', Lang.bind(this, function() { this._showMessageDialog(); })); this.application.add_action(messageAction);

// This closes the window when "Quit" is clicked in the menu let quitAction = new Gio.SimpleAction ({ name: 'quit' }); quitAction.connect('activate', Lang.bind(this, function() { this._window.destroy(); })); this.application.add_action(quitAction); },

_showMessageDialog: function () {

// Create a modal MessageDialog whose parent is the window this._messageDialog = new Gtk.MessageDialog ({ transient_for: this._window, modal: true, buttons: Gtk.ButtonsType.OK_CANCEL, message_type: Gtk.MessageType.WARNING, text: "This action will cause the universe to stop existing." });

this._messageDialog.connect ('response', Lang.bind(this, this._response_cb)); this._messageDialog.show(); },

// Callback function (aka signal handler) for the response signal _response_cb: function (messagedialog, response_id) {

// A simple switch that changes the main window's label switch (response_id) { case Gtk.ResponseType.OK: this.warningLabel.set_label ("*BOOM*\n"); break; case Gtk.ResponseType.CANCEL: this.warningLabel.set_label ("Good choice!\n"); break; case Gtk.ResponseType.DELETE_EVENT: this.warningLabel.set_label ("Dialog closed or cancelled.\n"); break; }

this._messageDialog.destroy();

}

});

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

# In-depth documentation

In this sample we used the following:

GMenu

GSimpleAction

Gtk.Application

Gtk.ApplicationWindow

Gtk.MessageDialog