Beispiel

Ein Beispielprogramm soll nun die Behandlung von ActionEvents veranschaulichen. Wir erzeugen zwei Buttons und ein Label. Auf beide Schaltflächen wird ein ActionListener installiert, der auf ihre Betätigung durch den Benutzer reagieren soll, indem er den Text des Labels ändert.

Bild 2: Das VoleEventHandlingExample

1    import jcontrol.ui.vole.Button;
2    import jcontrol.ui.vole.Frame;
3    import jcontrol.ui.vole.Label;
4    import jcontrol.ui.vole.event.ActionEvent;
5    import jcontrol.ui.vole.event.ActionListener;
6    
7    /**
8     * <p>This example demonstrates how to handle
9     * events within the GUI framework JControl/Vole.
10     * This program needs the image resource
11     * 'mouse.jcif'.</p>
12     *
13     * <p>(C) DOMOLOGIC Home Automation GmbH 2003-2005</p>
14     */
15    public class VoleEventHandlingExample
16                 extends Frame implements ActionListener {
17      // the Label
18      Label label;
19      // the right Button
20      Button button_right;
21    
22      /**
23       * Create two buttons and a label and add an ActionListener.
24       */
25      public VoleEventHandlingExample() {
26        // create the Buttons
27        Button b1 = new Button("Left Button", 2, 10, 60, 13);
28        button_right = new Button("Right Button", 66, 10, 60, 13);
29       
30        // add the ActionListener
31        b1.setActionListener(this);
32        button_right.setActionListener(this);
33       
34        // add the Buttons to the Frame
35        this.add(b1);
36        this.add(button_right);
37       
38        // create the Label
39        label = new Label("Please press a button!", 0, 30, 128, 10,
40                          Label.ALIGN_CENTER);
41        this.add(label);
42      }
43     
44     
45      /**
46       * This is the event handler. When a component fires an
47       * ActionEvent for us, this method is invoked.
48       */
49      public void onActionEvent(ActionEvent event) {
50        // check whether this is a BUTTON_PRESSED event
51        if (event.getType() == ActionEvent.BUTTON_PRESSED) {
52         
53          // recognize event's source by using getActionCommand()
54          if (event.getActionCommand().equals("Left Button"))
55            label.setLabel("You pressed the left button!", true);
56           
57          // recognize event's source by using getSource()
58          if (event.getSource() == button_right)
59            label.setLabel("The right button was hit!", true);
60        }
61      }
62     
63    
64      /**
65       * Instantiate and show the main frame.
66       */
67      public static void main(String[] args) {
68        new VoleEventHandlingExample().show();
69      }
70    }
Listing 1: VoleEventHandlingExample.java