How to Write an Internal Frame Listener - Java Tutorial 5.0 英文版

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How to Write an Internal Frame Listener

An InternalFrameListener is similar to a WindowListener. Like the window listener, the internal frame listener listens for events that occur when the "window" has been shown for the first time, disposed of, iconified, deiconified, activated, or deactivated. Before using an internal frame listener, please familiarize yourself with the WindowListener interface in How to Write Window Listeners.

The application shown in the following figure demonstrates internal frame events. The application listens for internal frame events from the Event Generator frame, displaying a message that describes each event.

[PENDING: New screenshot forthcoming.]

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Try this: 

1. Run InternalFrameEventDemo using Java^TM Web Start. Or, to compile and run the example yourself, consult the example index.
2. Bring up the Event Generator internal frame by clicking the Show internal frame button.
   You should see an "Internal frame opened" message in the display area.
3. Try various operations to see what happens. For example, click the Event Generator so that it gets activated. Click the Event Watcher so that the Event Generator gets deactivated. Click the Event Generator's decorations to iconify, maximize, minimize, and close the window.
   See How to Write Window Listeners for information on what kinds of events you'll see.

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Here is the internal frame event handling code:

public class InternalFrameEventDemo ...
		     implements InternalFrameListener ... {
    ...

    public void internalFrameClosing(InternalFrameEvent e) {
	displayMessage("Internal frame closing", e);
    }

    public void internalFrameClosed(InternalFrameEvent e) {
	displayMessage("Internal frame closed", e);
	listenedToWindow = null;
    }

    public void internalFrameOpened(InternalFrameEvent e) {
	displayMessage("Internal frame opened", e);
    }

    public void internalFrameIconified(InternalFrameEvent e) {
	displayMessage("Internal frame iconified", e);
    }

    public void internalFrameDeiconified(InternalFrameEvent e) {
	displayMessage("Internal frame deiconified", e);
    }

    public void internalFrameActivated(InternalFrameEvent e) {
	displayMessage("Internal frame activated", e);
    }

    public void internalFrameDeactivated(InternalFrameEvent e) {
	displayMessage("Internal frame deactivated", e);
    }

    void displayMessage(String prefix, InternalFrameEvent e) {
	String s = prefix + ": " + e.getSource(); 
	display.append(s + newline);
    }

    public void actionPerformed(ActionEvent e) {
	if (SHOW.equals(e.getActionCommand())) {
	    ...
	    if (listenedToWindow == null) {
	        listenedToWindow = new JInternalFrame("Event Generator",
	        				      true,  //resizable
	        				      true,  //closable
	        				      true,  //maximizable
	        				      true); //iconifiable
                //We want to reuse the internal frame, so we need to
                //make it hide (instead of being disposed of, which is
                //the default) when the user closes it.
        	listenedToWindow.setDefaultCloseOperation(
        				WindowConstants.HIDE_ON_CLOSE);

	        listenedToWindow.addInternalFrameListener(this);
	        ...
	    }
	} 
	...
    }
}

The Internal Frame Listener API

The InternalFrameListener Interface

The corresponding adapter class is InternalFrameAdapter.

Method	Purpose
internalFrameOpened(InternalFrameEvent)	Called just after the listened-to internal frame has been shown for the first time.
internalFrameClosing(InternalFrameEvent)	Called in response to a user request that the listened-to internal frame be closed. By default, JInternalFrame hides the window when the user closes it. You can use the JInternalFrame setDefaultCloseOperation method to specify another option, which must be either DISPOSE_ON_CLOSE or DO_NOTHING_ON_CLOSE (both defined in WindowConstants, an interface that JInternalFrame implements). Or by implementing an internalFrameClosing method in the internal frame's listener, you can add custom behavior (such as bringing up dialogs or saving data) to internal frame closing.
internalFrameClosed(InternalFrameEvent)	Called just after the listened-to internal frame has been disposed of.
internalFrameIconified(InternalFrameEvent) internalFrameDeiconified(InternalFrameEvent)	Called just after the listened-to internal frame is iconified or deiconified, respectively.
internalFrameActivated(InternalFrameEvent) internalFrameDeactivated(InternalFrameEvent)	Called just after the listened-to internal frame is activated or deactivated, respectively.

Each internal frame event method has a single parameter: an InternalFrameEvent object. The InternalFrameEvent class defines no generally useful methods. To get the internal frame that fired the event, use the getSource method, which InternalFrameEvent inherits from java.util.EventObject.

No other source files currently contain internal frame listeners. However, internal frame listeners are very similar to WindowListeners and several Swing programs have window listeners:

Example	Where Described	Notes
InternalFrameEventDemo	This section	Reports all internal frame events that occur on one internal frame to demonstrate the circumstances under which internal frame events are fired.
DialogDemo	Text Component Features	CustomDialog.java uses setDefaultCloseOperation instead of a window listener to determine what action to take when the user closes the window.
SliderDemo	How to Use Sliders	Listens for window iconify and deiconify events, so that it can stop the animation when the window isn't visible.

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