Trigger event only after repaint in Java Swing?

Question

I am making a simple board game in java, where I want to animate a dice roll. So I flash pictures of a dice like this:

public Timer roll_dice = new Timer(50, this);
...
public void actionPerformed(ActionEvent evt) {
        if(roll_dice.getDelay() > 500){
            roll_dice.setDelay(50);
            roll_dice.stop();
            movePiece();
        }else{
            roll_dice.setDelay(roll_dice.getDelay() + 50);
            dice_panel.repaint(0);
        }
    }
}

movePiece(){
    //do some more painting
}

So the die is going so show random numbers for a few times, and then slowly settle on a number. After that is done I would like to call the movePiece() method. However, as it is, the the repaint occurs sporadically and screws everything up so that movePiece() gets called before the dice roll is actually finished animating.

Does anyone have any ideas how I can call movePiece only after the final repaint has happened?

You should avoid having program logic be dependent on painting as you don't have full control over when or even if painting will occur. Rather than redrawing images and calling `repaint()`, why not simply put your rolling dice images into ImageIcons on program start up, and then in your Swing Timer, swap icons in a JLabel? Then stop your Timer when the delay gets long enough and in that if block, move your piece. — Hovercraft Full Of Eels, Mar 21 '12 at 16:26

Hovercraft Full Of Eels · Accepted Answer · 2012-03-21T16:43:55.347

So the die is going so show random numbers for a few times, and then slowly settle on a number. After that is done I would like to call the movePiece() method. However, as it is, the the repaint occurs sporadically and screws everything up so that movePiece() gets called before the dice roll is actually finished animating.

What worries me here is why your painting is occurring sporadically -- it simply shouldn't be doing that, and perhaps that is what you need to fix. I wonder if you're reading in the images from the file each time you do the drawing or some other cause for slowing the drawing down. If you need more help regarding this issue, then you'll have to give us more information on how you do your painting. Regardless, you should avoid having program logic be dependent on painting as you don't have full control over when or even if painting will occur.

Rather than redrawing images and calling repaint(), why not simply put your rolling dice images into ImageIcons on program start up, and then in your Swing Timer, swap icons in a JLabel? Then stop your Timer when the delay gets long enough and in that if block, move your piece.

So, assuming that you have several dice, each can be displayed by a JLabel that is held in an array of JLabel called diceLabels, and the ImageIcons can be held in an array called diceIcons. Then you can do something like:

  public void actionPerformed(ActionEvent e) {
     if (roll_dice.getDelay() > 500) {
        roll_dice.setDelay(50);
        roll_dice.stop();
        movePiece(); // I like this -- this shouldn't change
     } else {
        roll_dice.setDelay(roll_dice.getDelay() + 50);
        // dice_panel.repaint(0);
        for (JLabel dieLabel : diceLabels) {
           int randomIndex = random.nextInt(diceIcons.length);
           dieLabel.setIcon(diceIcons[randomIndex]);
        }
     }
  }

I like your logic on when you call movePiece() and I think that this should remain unchanged.

Thanks, that has made my life significantly easier. – wfbarksdale Mar 21 '12 at 18:13 — wfbarksdale, Mar 21 '12 at 18:13

Jakub Zaverka · Answer 2 · 2012-03-21T15:50:59.367

You can call the rolling in another thread and join() the current thread to the rolling one. That way the main code will wait until the roll thread dies (finished rolling).

public void actionPerformed(ActionEvent evt) {
    if(roll_dice.getDelay() > 500){
        Thread rollerThread = new RollerThread();
        rollerThread.start();
        rollerThread.join();
        movePiece();
    }
    else{
        roll_dice.setDelay(roll_dice.getDelay() + 50);
        dice_panel.repaint(0);
    }
}

private RollerThread extends Thread
{
    public void run(){
        roll_dice.setDelay(50);
        roll_dice.stop();
    }
}

However, this might not work with the EDT - because repaints should be scheduled to the queue. Maybe you can shedule the event using the SwingUtilities.invokeAndWait():

public void actionPerformed(ActionEvent evt) {
    Thread thread = new Thread(){
        public void run(){
            if(roll_dice.getDelay() > 500){
                SwingUtilities.invokeAndWait(new Runnable(){
                     public void run(){
                         roll_dice.setDelay(50);
                         roll_dice.stop();
                     }
                });
                movePiece();
            }
            else{
                 roll_dice.setDelay(roll_dice.getDelay() + 50);
                 dice_panel.repaint(0);
            }
        }
    };
    thread.start();
}

I am not sure that will fix the problem, because repaint gets called sporadically. Doesn't that just move the same problem to another thread? — wfbarksdale, Mar 21 '12 at 15:49

score 0 · Answer 3 · answered Mar 21 '12 at 15:52

Does anything change if you put that call to movePiece(); in a SwingUtilities.invokeLater(Runnable);?

if(roll_dice.getDelay() > 500){
    roll_dice.setDelay(50);
    roll_dice.stop();

    SwingUtilities.invokeLater(new Runnable() {
        public void run() { movePiece(); }
    });
}
...

Trigger event only after repaint in Java Swing?

3 Answers3