12.6. Shortcut Keys

// Have an OK button and set it as the default button
Button ok = new Button("OK");
ok.setClickShortcut(KeyCode.ENTER);
ok.addStyleName("primary");

The primary style name highlights a button to show the default button status; usually with a bolder font than usual, depending on the theme. The result can be seen in Figure 12.9, « Default Button with Click Shortcut ».

Figure 12.9. Default Button with Click Shortcut

// A field with Alt+N bound to it
TextField name = new TextField("Name (Alt+N)");
name.addShortcutListener(
        new AbstractField.FocusShortcut(name, KeyCode.N,
                                        ModifierKey.ALT));
layout.addComponent(name);

// A field with Alt+A bound to it
TextField address = new TextField("Address (Alt+A)");
address.addShortcutListener(
        new AbstractField.FocusShortcut(address, KeyCode.A,
                                        ModifierKey.ALT));
layout.addComponent(address);

The constructor of the FocusShortcut takes the field component as its first parameter, followed by the key code, and an optional list of modifier keys, as listed in Section 12.6.4, « Supported Key Codes and Modifier Keys ».

// Have the unmodified Enter key cause an event
Action action_ok = new ShortcutAction("Default key",
        ShortcutAction.KeyCode.ENTER, null);

// Have the C key modified with Alt cause an event
Action action_cancel = new ShortcutAction("Alt+C",
        ShortcutAction.KeyCode.C,
        new int[] { ShortcutAction.ModifierKey.ALT });

Action[] actions = new Action[] {action_cancel, action_ok};

public Action[] getActions(Object target, Object sender) {
    if (sender == myPanel)
        return actions;

    return null;
}

The constructor of ShortcutAction takes a symbolic caption for the action; this is largely irrelevant for shortcut actions in their current implementation, but might be used later if implementors use them both in menus and as shortcut actions. The second parameter is the key code and the third a list of modifier keys, which are listed in Section 12.6.4, « Supported Key Codes and Modifier Keys ».

The following example demonstrates the definition of a default button for a user interface, as well as a normal shortcut key, Alt+C for clicking the Cancel button.

public class DefaultButtonExample extends CustomComponent
                                  implements Handler {
    // Define and create user interface components
    Panel panel = new Panel("Login");
    FormLayout formlayout = new FormLayout();
    TextField username = new TextField("Username");
    TextField password = new TextField("Password");
    HorizontalLayout buttons = new HorizontalLayout();

    // Create buttons and define their listener methods.
    Button ok = new Button("OK", this, "okHandler");
    Button cancel = new Button("Cancel", this, "cancelHandler");

    // Have the unmodified Enter key cause an event
    Action action_ok = new ShortcutAction("Default key",
            ShortcutAction.KeyCode.ENTER, null);

    // Have the C key modified with Alt cause an event
    Action action_cancel = new ShortcutAction("Alt+C",
            ShortcutAction.KeyCode.C,
            new int[] { ShortcutAction.ModifierKey.ALT });

    public DefaultButtonExample() {
        // Set up the user interface
        setCompositionRoot(panel);
        panel.addComponent(formlayout);
        formlayout.addComponent(username);
        formlayout.addComponent(password);
        formlayout.addComponent(buttons);
        buttons.addComponent(ok);
        buttons.addComponent(cancel);

        // Set focus to username
        username.focus();

        // Set this object as the action handler
        System.out.println("adding ah");
        panel.addActionHandler(this);

        System.out.println("start done.");
    }

    /**
     * Retrieve actions for a specific component. This method
     * will be called for each object that has a handler; in
     * this example just for login panel. The returned action
     * list might as well be static list.
     */
    public Action[] getActions(Object target, Object sender) {
        System.out.println("getActions()");
        return new Action[] { action_ok, action_cancel };
    }

    /**
     * Handle actions received from keyboard. This simply directs
     * the actions to the same listener methods that are called
     * with ButtonClick events.
     */
    public void handleAction(Action action, Object sender,
                             Object target) {
        if (action == action_ok) {
            okHandler();
        }
        if (action == action_cancel) {
            cancelHandler();
        }
    }

    public void okHandler() {
        // Do something: report the click
        formlayout.addComponent(new Label("OK clicked. "
                + "User=" + username.getValue() + ", password="
                + password.getValue()));
    }

    public void cancelHandler() {
        // Do something: report the click
        formlayout.addComponent(new Label("Cancel clicked. User="
                + username.getValue() + ", password="
                + password.getValue()));
    }
}

Notice that the keyboard actions can currently be attached only to Panels and Windows. This can cause problems if you have components that require a certain key. For example, multi-line TextField requires the Enter key. There is currently no way to filter the shortcut actions out while the focus is inside some specific component, so you need to avoid such conflicts.