e621. Activating a Keystroke When Any Child Component Has Focus

Normally, a keystroke registered on 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 it or any child or descendant component has the focus. This type of keystroke activation condition is called WHEN_ANCESTOR_OF_FOCUSED_COMPONENT.

An example where this type of keystroke activation condition is useful is in the case of a scrollpane that handles scrolling navigation keystrokes even when the child component has the focus.

There are three types of activation conditions available: WHEN_FOCUSED, WHEN_ANCESTOR_OF_FOCUSED_COMPONENT, and WHEN_IN_FOCUSED_WINDOW. See e620 Activating a Keystroke When Any Component in the Window Has Focus for more details about these activation conditions.

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

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