# ComboBox (JavaScript)

Taryn Fox
jewelfox@fursona.net 2012
A customizable drop-down menu

# ComboBox

A ComboBox is an extremely customizable drop-down menu. It holds the equivalent of a TreeView widget that appears when you click on it, complete with a ListStore (basically a spreadsheet) that says what's in the rows and columns. In this example, our ListStore has the name of each option in one column, and the name of a stock icon in the other, which the ComboBox then turns into an icon for each option.

You select a whole horizontal row at a time, so the icons aren't treated as separate options. They and the text beside them make up each option you can click on.

Working with a ListStore can be time-consuming. If you just want a simple text-only drop-down menu, take a look at the ComboBoxText. It doesn't take as much time to set up, and is easier to work with.

# Bibliothèques à importer

#!/usr/bin/gjs

const GObject = imports.gi.GObject; 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 ComboBoxExample = new Lang.Class ({ Name: 'ComboBox Example',

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

// 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 builds the UI _onStartup: function () { this._buildUI (); },

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

// 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: "Welcome to GNOME", default_width: 200, border_width: 10 });

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 ListStore

// Create the liststore to put our options in this._listStore = new Gtk.ListStore(); this._listStore.set_column_types ([ GObject.TYPE_STRING, GObject.TYPE_STRING]);

This ListStore works like the one used in the TreeView example. We're giving it two columns, both strings, because one of them will contain the names of stock Gtk icons.

If we'd wanted to use our own icons that weren't already built in to GNOME, we'd have needed to use the gtk.gdk.Pixbuf type instead. Here are a few other types you can use:

GObject.TYPE_BOOLEAN -- True or false

GObject.TYPE_FLOAT -- A floating point number (one with a decimal point)

GObject.TYPE_STRING -- A string of letters and numbers

You need to put the line const GObject = imports.gi.GObject; at the start of your application's code, like we did in this example, if you want to be able to use GObject types.

// This array holds our list of options and their icons let options = [{ name: "Select" }, { name: "New", icon: Gtk.STOCK_NEW }, { name: "Open", icon: Gtk.STOCK_OPEN }, { name: "Save", icon: Gtk.STOCK_SAVE }];

// Put the options in the liststore for (let i = 0; i < options.length; i++ ) { let option = options[i]; let iter = this._listStore.append(); this._listStore.set (iter, [0], [option.name]); if ('icon' in option) this._listStore.set (iter, [1], [option.icon]); }

Here we create an array of the text options and their corresponding icons, then put them into the ListStore in much the same way we would for a TreeView's ListStore. We only want to put an icon in if there's actually an icon in the options array, so we make sure to check for that first.

"Select" isn't really an option so much as an invitation to click on our ComboBox, so it doesn't need an icon.

# Creating the ComboBox

// Create the combobox this._comboBox = new Gtk.ComboBox({ model: this._listStore});

Each ComboBox has an underlying "model" it takes all its options from. You can use a TreeStore if you want to have a ComboBox with branching options. In this case, we're just using the ListStore we already created.

// Create some cellrenderers for the items in each column let rendererPixbuf = new Gtk.CellRendererPixbuf(); let rendererText = new Gtk.CellRendererText();

// Pack the renderers into the combobox in the order we want to see this._comboBox.pack_start (rendererPixbuf, false); this._comboBox.pack_start (rendererText, false);

// Set the renderers to use the information from our liststore this._comboBox.add_attribute (rendererText, "text", 0); this._comboBox.add_attribute (rendererPixbuf, "stock_id", 1);

This part, again, works much like creating CellRenderers and packing them into the columns of a TreeView. The biggest difference is that we don't need to create the ComboBox's columns as separate objects. We just pack the CellRenderers into it in the order we want them to show up, then tell them to pull information from the ListStore (and what type of information we want them to expect).

We use a CellRendererText to show the text, and a CellRendererPixbuf to show the icons. We can store the names of the icons' stock types as strings, but when we display them we need a CellRenderer that's designed for pictures.

Just like with a TreeView, the "model" (in this case a ListStore) and the "view" (in this case our ComboBox) are separate. Because of that, we can do things like have the columns in one order in the ListStore, and then pack the CellRenderers that correspond to those columns into the ComboBox in a different order. We can even create a TreeView or other widget that shows the information in the ListStore in a different way, without it affecting our ComboBox.

// Set the first row in the combobox to be active on startup this._comboBox.set_active (0);

// Connect the combobox's 'changed' signal to our callback function this._comboBox.connect ('changed', Lang.bind (this, this._onComboChanged));

We want the "Select" text to be the part people see at first, that gets them to click on the ComboBox. So we set it to be the active entry. We also connect the ComboBox's changed signal to a callback function, so that any time someone clicks on a new option something happens. In this case, we're just going to show a popup with a little haiku.

// Add the combobox to the window this._window.add (this._comboBox);

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

Finally, we add the ComboBox to the window, and tell the window to show itself and everything inside it.

# Function which handles your selection

_selected: function () {

// The silly pseudohaiku that we'll use for our messagedialog let haiku = ["", "You ask for the new\nwith no thought for the aged\nlike fallen leaves trod.", "Like a simple clam\nrevealing a lustrous pearl\nit opens for you.", "A moment in time\na memory on the breeze\nthese things can't be saved."];

We're going to create a pop-up MessageDialog, which shows you a silly haiku based on which distro you select. First, we create the array of haiku to use. Since the first string in our ComboBox is just the "Select" message, we make the first string in our array blank.

// Which combobox item is active? let activeItem = this._comboBox.get_active();

// No messagedialog if you choose "Select" if (activeItem != 0) { this._popUp = new Gtk.MessageDialog ({ transient_for: this._window, modal: true, buttons: Gtk.ButtonsType.OK, message_type: Gtk.MessageType.INFO, text: haiku[activeItem]});

// Connect the OK button to a handler function this._popUp.connect ('response', Lang.bind (this, this._onDialogResponse));

// Show the messagedialog this._popUp.show(); }

},

Before showing a MessageDialog, we first test to make sure you didn't choose the "Select" message. After that, we set its text to be the haiku in the array that corresponds to the active entry in our ComboBoxText. We do that using the get_active method, which returns the number ID of your selection.

Other methods you can use include get_active_id, which returns the text ID assigned by append, and get_active_text, which returns the full text of the string you selected.

After we create the MessageDialog, we connect its response signal to the _onDialogResponse function, then tell it to show itself.

_onDialogResponse: function () {

this._popUp.destroy ();

}

});

Since the only button the MessageDialog has is an OK button, we don't need to test its response_id to see which button was clicked. All we do here is destroy the popup.

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

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

# Complete code sample

# In-depth documentation

Dans cet exemple, les éléments suivants sont utilisés :

Gtk.Application

Gtk.ApplicationWindow

Gtk.CellRendererPixbuf

Gtk.CellRendererText

Gtk.ComboBox

Gtk.ListStore

Gtk.MessageDialog

Gtk.TreeIter