JLabel不会改变颜色

Question

Part of my function looks like this

jLabel2.setBackground(Color.YELLOW);
jLabel2.setText("Status : Idle");

boolean ok=cpu21.RestartSSH();

if(ok){
    jLabel2.setBackground(Color.GREEN);
    jLabel2.setText("Status : Run");    
}

Before I enter in function label is Green and Run, but when I come in function it doesn't chabge color to Yellow ( function RestartSSH is executing 5-6 sec, but during that time labels doesn't change colors and captures ). Where I make mistake in painting ?

Answer 1

• Make your JLabel opaque so you can set its background colour.
• Perform RestartSSH in a separate thread, or your GUI won't respond to events.

Example:

final JLabel jLabel2 = new JLabel("HELLO");
jLabel2.setOpaque(true);
jLabel2.setBackground(Color.YELLOW);
jLabel2.setText("Status : Idle");

//perform SSH in a separate thread
Thread sshThread = new Thread(){
    public void run(){
        boolean ok=cpu21.RestartSSH();
        if(ok){
           //update the GUI in the event dispatch thread
           SwingUtilities.invokeLater(new Runnable() {
               public void run() {
                   jLabel2.setBackground(Color.GREEN);
                   jLabel2.setText("Status : Run");
               }
           });
        }
    }
};
sshThread.start();

(Update: added call to SwingUtilities.invokeLater )

Answer 2

JLabels is opaque by default, so their's background isn't painted by default. Try with:

jLabel2.setOpaque(true);

or maybe you have to call repaint after changing the color:

jLabel2.repaint();

Answer 3

I suspect that your restartSSH() method is blocking the event dispatch thread . One approach is to use a SwingWorker , as suggested in this example . This would allow you to show the progress of the restart process and set the label appropriately when done.