e620. Activating a Keystroke When Any Component in the Window Has Focus

Posted 2021-01-04 borter

Normally, a keystroke registered to a component is activated when the component has the focus. This type of activation condition is called WHEN_FOCUSED. It is possible to specify that a keystroke be activated if any component (including itself) in the window has the focus. This type of keystroke activation condition is called WHEN_IN_FOCUSED_WINDOW.

Keyboard accelerators use this type of keystroke activation condition. For example, in many applications, regardless of which component has the focus, typing F1 in an active window causes a help window to appear.

There are three types of activation conditions available: WHEN_FOCUSED, WHEN_ANCESTOR_OF_FOCUSED_COMPONENT, and WHEN_IN_FOCUSED_WINDOW. When a key is typed, the focused component is checked for a registered keystroke to handle the typed key. If found, the action bound to the keystroke is invoked. If not found, the set of WHEN_ANCESTOR_OF_FOCUSED_COMPONENT keystrokes is searched for a handler of the typed key. WHEN_ANCESTOR_OF_FOCUSED_COMPONENT is described in e621 Activating a Keystroke When Any Child Component Has Focus. If none are found still, the set of WHEN_IN_FOCUSED_WINDOW keystrokes is searched for a handler of the typed key.

In non-WHEN_FOCUSED activated keystrokes, the source of the resulting action event is the component to which the keystroke is registered, not the focused component.

    // To create an action, see e855 创建一个事件
    
    // Register keystroke
    component.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW).put(
        KeyStroke.getKeyStroke("F2"), action.getValue(Action.NAME));
    
    // Register action
    component.getActionMap().put(action.getValue(Action.NAME), action);

 

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