How do I remove an old JPanel and add a new one?

问题:

I would like to remove an old JPanel from the Window (JFrame) and add a new one. How should I do it?

I tried the following:

public static void showGUI() {
    JFrame frame = new JFrame("Colored Trails");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);       
    frame.add(partnerSelectionPanel);
    frame.setSize(600,400);
    frame.setVisible(true);
}

private static void updateGUI(final int i, final JLabel label, final JPanel partnerSelectionPanel) {
    SwingUtilities.invokeLater( 
        new Runnable() {
            public void run() {
                label.setText(i + " seconds left.");
            }
            partnerSelectionPanel.setVisible(false); \\ <------------
        }
    );
}

My code updates the "old" JPanel and then it makes the whole JPanel invisible, but it does not work. The compiler complains about the line indicated with <------------. It writes: <identifier> expected, illegal start of type.

ADDED:

I have managed to do what I needed and I did it in the following way:

public static void showGUI() {
    frame = new JFrame("Colored Trails");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);       
    frame.add(partnerSelectionPanel);
    //frame.add(selectionFinishedPanel);
    frame.setSize(600,400);
    frame.setVisible(true);
}

public static Thread counter = new Thread() {
    public void run() {
        for (int i=4; i>0; i=i-1) {
            updateGUI(i,label);
            try {Thread.sleep(1000);} catch(InterruptedException e) {};
        }
        partnerSelectionPanel.setVisible(false);
        frame.add(selectionFinishedPanel);
    }
};

It works but it does not look to me like a safe solution for the following reasons:

1. I change and add elements to the JFrame from another thread.
2. I add a new JPanel to a JFrame, after I have already "packed" the JFrame and made it visible.

Should I be doing that?

回答1:

setVisible(false), even in the correct place, will not actually remove the panel from the container. If you want to replace the panel do this:

frame.getContentPane().remove(partnerSelectionPanel);
frame.add(new JPanel());
frame.getContentPane().invalidate();
frame.getContentPane().validate();

Note that frame.getContentPane().add(Component) is the same as frame.add(Component) - the components are actually contained within the content pane.

回答2:

Don't forget or overlook the approach of using the Layout, namely the CardLayout as the Frames Layout, to allow this type of behavior (This is a good strategy for a "Wizard" for example). One advantage to this is it doesn't cause any weird flash or draw effects as that is what this Layout is meant to do--Allow a panels to be swapped out, assuming they have exclusive "real estate" or can share the same areas (i.e. "Wizard" like behavior.)

回答3:

partnerSelectionPanel.setVisible(false); \\ <------------

This line is actualy out the method run.

You probably want something like this:

public void run() {
   label.setText(i + " seconds left.");
   try {
      Thread.sleep (i * 1000);
   } catch (InterruptedException e) {
      handleException (e);
   }
   partnerSelectionPanel.setVisible(false);
}

回答4:

You can use

  Frame.setContentPane(jPanel);