更新 JButton 背景颜色的问题

Question

I have to maintain a very old and badly written Java software. And i ran into a problem after an update: There are some buttons that change the shown panel in a card layout. There are handlers registered, and that part seems to work. Now the second part of these buttons is changing the background color. But this change is not triggered by the click. At least not directly. Clicking the button triggers a message to some machine, that machine then responds with a status, and that status then leads to a color change of that button.

This color change ceised to work after the last update. So basically there are 2 questions:

1. I have the vague idea that this lack of color changing is related to "do not update GUI elements outside the event dispatch thread". How probable is it that this is the root of the problem? There is an observation which lead to that assumption: Moving around the mouse triggers the color change after some time.

2. If yes, what would be the easiest way to cope with that? Implement a PropertyChangeListener on these buttons? Or any other (better) way?

Since the nice people here insist on seeing some code:

Color[] backgroundColors = {
    ColorExt.btnCol,                // 0 0 not prepare mode, not selected
    ColorExt.darkGreen,             // 0 1 not prepare mode, selected
    ColorExt.YELLOW,                // 1 0 prepare mode, not selected
    ColorExt.dimOrange,             // 1 1 prepare mode, selected
};
JButton[] btn = { mainframe.jBtnLoader1, mainframe.jBtnLoader2, mainframe.jBtnLoader3 };
for (int ldr=0; ldr<3; ldr++) {
    int colorIdx = 0;
    if ((inCellViewFromLoader[ldr][124] & 16) != 0) 
        colorIdx = 2;                   // bLoaderError = true => prepare
    if (mainframe.currentSelectedLoader == ldr) { 
        colorIdx += 1;                  // selected
    }
    btn[ldr].setBackground(backgroundColors[colorIdx]);
}

There is nothing special about it though. This code itself is not the problem. My assumption is, since this code is executed in some network thread, not in the event dispatch thread, that is the root of the problem.

Answer 1

So, according to MadProgrammers suggestion, i made a small utility class:

/**
 * Class to be instantiated in a call to EventQueue.invokeLater(), so the
 * background color of the given component is updated in the Event
 * Dispatch Thread.
 * 
 *
 */
public class ColorChanger implements java.lang.Runnable {

private Color color = Color.WHITE;
private JComponent component = null;

public ColorChanger(JComponent component, Color color) {
    super();
    this.component = component;
    this.color = color;
}

@Override
public void run() {
    if (component != null) {
        component.setBackground(color);
    }
}

}

And then changed the line btn[ldr].setBackground(backgroundColors[colorIdx]); to: EventQueue.invokeLater(new ColorChanger(btn[ldr], backgroundColors[colorIdx]));

At least that looks reasonable. It will take some time though until i can test this at the customers site.