Question

I have (what should be) a simple problem to tackle and I’m open to other ways to solve it. I am open to other solutions.

The problem:
We are using java swing to display the graphics of a turn-based, tile-based game. I’m using jlabels with icons, absolutely positioned.

To animate the movement, I am using a swing timer that updates the location by 4 pixels at a time, slowly moving the sprite right, left, etc.

To achieve this initially, I was running a timer, which works wonderfully. The problem comes in when I try to move down, then move right.

The sprite moves down, never moves right, and if I watch the execution with some console printing, it’s clear to see that both timers are running at the same time. I’ve done a fair amount of digging on the internet and I wasn’t able to find a way to tell a swing timer not to execute until the first timer has stopped, and if I try to busy-wait until one timer finishes (yuck) the UI never displays at all (clearly a step in the wrong direction.)

Now I can convert away from timers altogether and either have the sprite teleport to its new location, or use some awful busy-wait movement scheme, but I’m hoping some kind soul has a solution.

In short: I need a way to run a swing timer for a set period of time, stop it, and then start a new timer, so that they do not overlap. Preferably this method would allow each timer to be in its own method, and I could then call the methods one after the other.

Thanks in advance for any advice you might have.

Edit: Expanded example code. If a full scsse is a requirement for your advice then I’m sorry to have wasted your time, because the full code is a beast. This sample code does not work at all as it stands, sorry, but it should illustrate the point.

So. We have two functions, each with a timer that runs an animation cycle, one for moving down and right diagonally, one for moving straight down.

public class TestClass {
    static int counter = 0;
    static int counter2 = 0;
    static Timer timerC;
    static Timer timerX;

    public static void main(String[] args) {
        moveC();
        moveX();
    }

    public static void moveC() {
        int delay = 200; // milliseconds

        timerC = new Timer(delay, null);
        timerC.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent evt) {
                if (counter < 32) {
                    counter = counter + 4;
                    System.out.println("*C*");
                } else {
                    timerC.stop();
                    System.out.println("*C STOP*");
                }

            }
        });
        timerC.start();
    }

    public static void moveX() {
        int delay = 200; // milliseconds

        timerX = new Timer(delay, null);
        timerX.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent evt) {
                if (counter < 32) {
                    counter = counter + 4;
                    System.out.println("*X*");
                } else {
                    timerX.stop();
                    System.out.println("*X STOP*");
                }

            }
        });
        timerX.start();
    }

}

What I would want to see here eventually would be

*C*
*C*
*C*
*C*
*C STOP*
*X*
*X*
*X*
*X*
*X STOP*

What I actually get is

*C*
*X*
*C*
*X*
*C*
*X*
*C*
*X*
*C STOP*
*X STOP*

The point I’m trying to get at here is running one animation cycle to completion, then the other.

Thanks again.

Answer 1

Don’t use multiple Timers, but rather only one Timer that deals with each direction as it’s needed. You need some type of queue to hold the direction information, either a formal queue or a collection that you use as a queue (first in, first out), and then have your Timer extract the direction from this queue as it’s running. For example, here I use my JList’s model as my queue by removing and using the Direction that was added first (at the top of the JList):

import java.awt.GridLayout;
import java.awt.event.*;
import javax.swing.*;

public class TimerPlay extends JPanel {
   private DefaultListModel directionJListModel = new DefaultListModel();
   private JList directionJList = new JList(directionJListModel);
   JButton startTimerButton = new JButton(
         new StartTimerBtnAction("Start Timer"));

   public TimerPlay() {
      ActionListener directionBtnListener = new ActionListener() {

         @Override
         public void actionPerformed(ActionEvent actEvt) {
            String actionCommand = actEvt.getActionCommand();
            Direction dir = Direction.valueOf(actionCommand);
            if (dir != null) {
               directionJListModel.addElement(dir);
            }
         }
      };
      JPanel directionBtnPanel = new JPanel(new GridLayout(0, 1, 0, 10));
      for (Direction dir : Direction.values()) {
         JButton dirBtn = new JButton(dir.toString());
         dirBtn.addActionListener(directionBtnListener);
         directionBtnPanel.add(dirBtn);
      }

      add(directionBtnPanel);
      add(new JScrollPane(directionJList));
      add(startTimerButton);
   }

   private class StartTimerBtnAction extends AbstractAction {
      protected static final int MAX_COUNT = 20;

      public StartTimerBtnAction(String title) {
         super(title);
      }

      @Override
      public void actionPerformed(ActionEvent arg0) {
         startTimerButton.setEnabled(false);

         int delay = 100;
         new Timer(delay, new ActionListener() {
            private int count = 0;
            private Direction dir = null;

            @Override
            public void actionPerformed(ActionEvent e) {
               if (count == MAX_COUNT) {
                  count = 0; // restart
                  return;
               } else if (count == 0) {
                  if (directionJListModel.size() == 0) {
                     ((Timer)e.getSource()).stop();
                     startTimerButton.setEnabled(true);
                     return;
                  }
                  // extract from "queue"
                  dir = (Direction) directionJListModel.remove(0);
               }
               System.out.println(dir); // do movement here
               count++;

            }
         }).start();
      }
   }

   private static void createAndShowGui() {
      TimerPlay mainPanel = new TimerPlay();

      JFrame frame = new JFrame("TimerPlay");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }

}

enum Direction {
   UP, DOWN, LEFT, RIGHT;
}