No último tutorial, nós aprendemos como criar widgets tipo Labels (rótulos), Images (imagens) e Buttons (botões). Aqui, nós vamos aprender como fazer para Buttons e outros widgets de entrada realmente fazer as coisas, escrevendo funções que lidam com os sinais que elas enviam quando elas são clicadas ou recebem interação.
No GNOME, widgets com os quais você pode interagir, como Buttons e Switches, enviam sinais quando são clicados ou ativados. Um Button, por exemplo, envia o sinal de "clicado" quando alguém clica nele. Quando isto acontece, o GNOME procura a parte do código que diz o que deve ser feito.
Como nós vamos escrever esse código? Conectando aquele sinal de "clicado" do Button a uma função de chamada, que é uma função que você escreve apenas para lidar com esse sinal. Então, quando você aplica aquele sinal, a função conectada a ele será executada.
Aqui está um exemplo extremamente básico:
Esse ApplicationWindow possui um Button e um Label, organizados em uma Grid. Quando o Button é clicado, uma variável que mantém o número de cookies é incrementada em 1 e o Label que mostra quantos cookies existem será atualizado.
Os cookies neste exemplo não são os mesmos que aqueles que você obtém de sites, que armazenam a informação da sua sessão e podem manter rastro de quais sites você visitou. Eles são apenas biscoitos imaginários. Você pode preparar alguns de verdade, se quiser.
Aqui está o código básico, padrão que vai na inicialização do aplicativo, antes de começar a criação da janela e widgets. Além do aplicativo ter um nome único, a maior alteração em relação ao padrão é que nós criamos uma variável global bem perto do começo, para manter o número de cookies.
Take a look at the part that uses our application's connect method and bind, to connect its activate and startup signals to the functions that present the window and build the UI. We're going to do the same thing with our Button when we get to it, except that we're going to connect its "clicked" signal instead.
Buttons aren't the only input widgets in our GTK+ toolbox. We can also use switches, like the one in this example. Switches don't have a label property, so we have to create a separate Label that says what it does to go next to it.
A Switch has two positions, Off and On. When a Switch is turned on, its text and background color change, so you can tell which position it's in.
You may have seen Switches like these in GNOME's accessibility menu, which let you turn features like large text and the on-screen keyboard on and off. In this case, the Switch controls our imaginary cookie dispenser. If the Switch is turned on, you can get cookies by clicking the "Get a cookie" Button. If it's turned off, clicking the Button won't do anything.
You can get to the accessibility menu by clicking on the outline of a human, near your name in the upper-right corner of the screen.
Here's how we create the Switch:
We don't actually need to connect the Switch to anything. All we need to do is write an if statement in our _getACookie function, to check to see if the Switch is turned on. If we wanted to make something happen as soon as you flip the Switch, though, we would connect its notify::active signal, like so:
A Switch is set to the off position by default. If we wanted the Switch to start out turned on, we would set the value of its active property to true when we create it.
Let's just create it normally, though, and then create the Label that goes with it. We want the Switch and the Label to be kept right next to each other, so we'll create a Grid just for them, then put that Grid in our larger Grid that holds all the widgets inside it. Here's what the code looks like to create all that:
And now we arrange everything in the larger Grid like so.
Now we change the _getACookie function so that it checks to see if the cookie dispenser is turned on. We do that by using the Switch's get_active method. It returns true if the Switch is turned on, and false if the Switch is turned off.
When a method is used in an if statement like this, the code inside the if statement is executed if the method returns true.
Another type of input widget we can use is called the RadioButton. You create them in groups, and then only one RadioButton in a group can be selected at a time. They're called RadioButtons because they work like the channel preset button in old-style car radios. The radio could only be tuned to one station at a time, so whenever you pressed one button in, another would pop back out.
First off, let's change our ApplicationWindow's name and increase its border_width property, so that our widgets aren't packed in too tightly. The border_width is the number of pixels between any widget and the edge of the window.
After that, we create the RadioButtons. Remember how they're created in groups? The way we do that, is we set each new RadioButton's group property to the name of another RadioButton.
Next, we create a Grid for the RadioButtons. Remember, we don't have to arrange things in Grids in the same order that we create them in.
Normally, the RadioButton that's selected by default is the one that's the name of the group. We want the first "Not cookie" button to be selected by default, though, so we use its set_active method.
We could also set its active property to true when we create it.
Now we arrange everything in our main Grid like usual ...
And then we change our _getACookie function to test to see if the cookie button is the one that's selected.
The last input widget we're going to cover is the Entry widget, which is used for single-line text entry.
If you need to be able to enter in a whole paragraph or more, like if you are building a text editor, you'll want to look at the much more customizable TextView widget.
After we change the window's name, we create the Entry widget.
Next, we arrange everything in the Grid ...
And now we modify _getACookie's if statement again, using the Entry's get_text method to retrieve the text that you entered into it and see if you spelled "cookie" right. We don't care whether you capitalize "cookie" or not, so we use JavaScript's built-in toLowerCase method to change the Entry's text to all lower case inside the if statement.
An Entry widget doesn't have a label property, which is a set text string that the user can't change. (You can't normally change the label on a Button, for instance.) Instead, it has a text property, which changes to match what the user types in.
Keep reading, if you'd like to see the complete code for each version of our cookie maker application.
The main JavaScript tutorials page has more detailed code samples for each input widget, including several not covered here.
#!/usr/bin/gjs
imports.gi.versions.Gtk = '3.0';
const Gtk = imports.gi.Gtk;
// We start out with 0 cookies
var cookies = 0;
class GettingTheSignal {
// Create the application itself
constructor() {
this.application = new Gtk.Application();
// Connect 'activate' and 'startup' signals to the callback functions
this.application.connect('activate', this._onActivate.bind(this));
this.application.connect('startup', this._onStartup.bind(this));
}
// Callback function for 'activate' signal presents window when active
_onActivate() {
this._window.present();
}
// Callback function for 'startup' signal builds the UI
_onStartup() {
this._buildUI();
}
// Build the application's UI
_buildUI() {
// Create the application window
this._window = new Gtk.ApplicationWindow({
application: this.application,
window_position: Gtk.WindowPosition.CENTER,
default_height: 200,
default_width: 400,
title: "Click the button to get a cookie!"});
// Create the label
this._cookieLabel = new Gtk.Label ({
label: "Number of cookies: " + cookies });
// Create the cookie button
this._cookieButton = new Gtk.Button ({
label: "Get a cookie" });
// Connect the cookie button to the function that handles clicking it
this._cookieButton.connect ('clicked', this._getACookie.bind(this));
// Create the switch that controls whether or not you can win
this._cookieSwitch = new Gtk.Switch ();
// Create the label to go with the switch
this._switchLabel = new Gtk.Label ({
label: "Cookie dispenser" });
// Create a grid for the switch and its label
this._switchGrid = new Gtk.Grid ({
halign: Gtk.Align.CENTER,
valign: Gtk.Align.CENTER });
// Put the switch and its label inside that grid
this._switchGrid.attach (this._switchLabel, 0, 0, 1, 1);
this._switchGrid.attach (this._cookieSwitch, 1, 0, 1, 1);
// Create a grid to arrange everything else inside
this._grid = new Gtk.Grid ({
halign: Gtk.Align.CENTER,
valign: Gtk.Align.CENTER,
row_spacing: 20 });
// Put everything inside the grid
this._grid.attach (this._cookieButton, 0, 0, 1, 1);
this._grid.attach (this._switchGrid, 0, 1, 1, 1);
this._grid.attach (this._cookieLabel, 0, 2, 1, 1);
// Add the grid to the window
this._window.add (this._grid);
// Show the window and all child widgets
this._window.show_all();
}
_getACookie() {
// Is the cookie dispenser turned on?
if (this._cookieSwitch.get_active()) {
// Increase the number of cookies by 1 and update the label
cookies++;
this._cookieLabel.set_label ("Number of cookies: " + cookies);
}
}
};
// Run the application
let app = new GettingTheSignal ();
app.application.run (ARGV);
#!/usr/bin/gjs
imports.gi.versions.Gtk = '3.0';
const Gtk = imports.gi.Gtk;
// We start out with 0 cookies
var cookies = 0;
class GettingTheSignal {
// Create the application itself
constructor() {
this.application = new Gtk.Application();
// Connect 'activate' and 'startup' signals to the callback functions
this.application.connect('activate', this._onActivate.bind(this));
this.application.connect('startup', this._onStartup.bind(this));
}
// Callback function for 'activate' signal presents window when active
_onActivate() {
this._window.present();
}
// Callback function for 'startup' signal builds the UI
_onStartup() {
this._buildUI();
}
// Build the application's UI
_buildUI() {
// Create the application window
this._window = new Gtk.ApplicationWindow({
application: this.application,
window_position: Gtk.WindowPosition.CENTER,
default_height: 200,
default_width: 400,
border_width: 20,
title: "Spell 'cookie' to get a cookie!"});
// Create the text entry field
this._spellCookie = new Gtk.Entry ();
// Create the cookie button
this._cookieButton = new Gtk.Button ({
label: "Get a cookie" });
// Connect the cookie button to the function that handles clicking it
this._cookieButton.connect ('clicked', this._getACookie.bind(this));
// Create the label
this._cookieLabel = new Gtk.Label ({
label: "Number of cookies: " + cookies });
// Create a grid to arrange everything inside
this._grid = new Gtk.Grid ({
halign: Gtk.Align.CENTER,
valign: Gtk.Align.CENTER,
row_spacing: 20 });
// Put everything inside the grid
this._grid.attach (this._spellCookie, 0, 0, 1, 1);
this._grid.attach (this._cookieButton, 0, 1, 1, 1);
this._grid.attach (this._cookieLabel, 0, 2, 1, 1);
// Add the grid to the window
this._window.add (this._grid);
// Show the window and all child widgets
this._window.show_all();
}
_getACookie() {
// Did you spell "cookie" correctly?
if ((this._spellCookie.get_text()).toLowerCase() == "cookie") {
// Increase the number of cookies by 1 and update the label
cookies++;
this._cookieLabel.set_label ("Number of cookies: " + cookies);
}
}
};
// Run the application
let app = new GettingTheSignal ();
app.application.run (ARGV);