Java : ignore single click on double click?

Question

can anyone think of a good way to ignore the single click that comes with a double-click in Java?

I'm looking to have different behaviors for each such that:

• single-click paints crosshairs on the click point
• double-click selects an object on the screen, but should not paint crosshairs on the click point

... can anyone think of a way to do this? Some sort of timer set-up maybe? An ideas appreciated:-)

<disclaimer>...and yes, I know I'm committing a most heinous usability / UI faux pas. </disclaimer>

EDIT #2:

Even though this works the delay due to the timer is maddening - I'm abandoning this solution, and using middle-click for selection instead of double-click...

EDIT:

Thanks cgull - this is what I was able to come up with given your confirmation that there's no easy way to do this (note that if I set the timer < 200 odd racing is seen between the click & the timer, but as long as I set this to a value > 200 things work just peachy):

public void mouseClicked(MouseEvent e) {
    System.out.println( "Click at (" + e.getX() + ":" + e.getY() + ")" );
    if (e.getClickCount() == 2) {  
        System.out.println( "  and it's a double click!");
        wasDoubleClick = true;
    }else{
        Integer timerinterval = (Integer) 
          Toolkit.getDefaultToolkit().getDesktopProperty(
                      "awt.multiClickInterval");
        timer = new Timer(timerinterval.intValue(), new ActionListener() {
            public void actionPerformed(ActionEvent evt) {
                if (wasDoubleClick) {
                    wasDoubleClick = false; // reset flag
                } else {
                    System.out.println( "  and it's a simple click!");
                }
            }    
        });
        timer.setRepeats(false);
        timer.start();
    }
}

Answer 1

Indeed you'll need to set up a Timer in your overridden mouseClicked() method of your MouseAdapter to detect the time interval between the two clicks. The default interval in ms can be found by querying Toolkit.getDefaultToolkit().getDesktopProperty("awt.multiClickInterval") . If another mouse click is detected before the timer expires, then you have a double-click, else once the timer expires, you can process the single-click.

Answer 2

Actually I think there is a simpler solution (use InputEvent's getWhen() method):

class DCListener extends MouseAdapter{

    private long maxTimeBetweenClicks; // in millis
    private long firstClickTime=0;
    private Runnable eventHandler;

    public DCListener(long maxTimeBetweenClicks,Runnable eventHandler){
        this.maxTimeBetweenClicks=maxTimeBetweenClicks;
        this.eventHandler=eventHandler;
    }

    public void mouseClicked(MouseEvent e){

        if((e.getWhen()-firstClickTime)<=maxTimeBetweenClicks){
            firstClickTime=0; // 3 clicks are not 2 double clicks
            eventHandler.run();
        }else{
            firstClickTime=e.getWhen();
        }

    }
}

Answer 3

An alternative solution:

I figured out this before I found the solution in this question. The idea is the same, use a timer, although more complicated :).

Use SwingWorker :

class BackgroundClickHandler extends SwingWorker<Integer, Integer> {
  @Override
  protected Integer doInBackground() throws Exception {
    Thread.sleep(200);
    // Do what you want with single click
    return 0;
  }

}

In mouseClicked() method you can do something like this:

 if (event.getClickCount() == 1) {
  // We create a new instance everytime since
  // the execute() method is designed to be executed once
  clickHandler = new BackgroundClickHandler();

  try {
    clickHandler.execute();
  } catch(Exception e) {
    writer.println("Here!");
  }
}

if (event.getClickCount() == 2) {
  clickHandler.cancel(true);

  //Do what you want with double click
}

I hope it be useful.

Answer 4

Have you tried implementing the MouseListener interface already?

I think MouseEvent has a click count method ( or property ) to know that.

I bet you have gone through that already, so what is the problem you're facing there?

Probably what you can do is to code the time interval elapsed between a single and a double click with a thread or something.

So a single click will only be valid if another click is not issued in let's say 300 ms. ( something configurable )

The idea is:

public void listen for the single click() 
    if (  in x time there has not been another click  ) 
    then 
        we have a single click
        proceed with your single click handling
    else 
        we have a double click
       proceed with your double click handling

Or something like that.

Answer 5

Thanks to this thread I made this simillar solution, that is the way I would imagine it. It keeps a Timer thread (where single click events are scheduled with a 200ms delay) alive all the time - this could upset someone, but afterall starting a thread is the expensive stuff, isn't it?

Track of the last TimerTask is kept and it's cancel() method is called if a double click arrives. A double click cancels its single click if it arrives within 200ms, or has no effect if late.

I use JavaFX, but that should not matter. The core stuff is the Timer and TimerTask .

import java.util.Timer;
import java.util.TimerTask;
import javafx.fxml.FXML;
import javafx.scene.input.MouseEvent;
import javafx.scene.input.MouseButton;

class SomeController {
    private static final long MAX_MULTICLICK_INTERVAL = 200; //the milliseconds delay
    private final Timer singleLeftClickTimer = new Timer(true); //isDeamon = true, will be terminated with the rest of the app
    private TimerTask lastSingleClickTask;

    private void onMouseClickedFiltered(MouseEvent event) {
        //TODO process clicks
        //For the primary button you get only single clicks that were not followed by double clicks within 200ms
        //Double clicks and all clicks of other buttons go through unchanged
    }

    @FXML
    private void onMouseClicked(MouseEvent event) {
        if (event.getButton() != MouseButton.PRIMARY) {
            onMouseClickedFiltered(event);
        } else if (event.getClickCount() == 2) {
            lastSingleClickTask.cancel(); //if 200ms passed from associated single click, this will have no effect
            onMouseClickedFiltered(event);
        } else if (event.getClickCount() == 1) {
            lastSingleClickTask = new TimerTask() {
                @Override
                public void run() {
                    onMouseClickedFiltered(event);
                }
            };
            singleLeftClickTimer.schedule(lastSingleClickTask, MAX_MULTICLICK_INTERVAL);
        } // else: might swallow primary button clicks with clickCount outside 1 and 2 which is ok for me
    }
}

Answer 6

Looking up the answer to this question I was thinking about a different solution. Couldn't find it so I share my thoughts:

The delay the other solutions introduce in the single click processing are a little painful because you get this delayed response. However those solutions are the simplest to implement and don't bother the rest of the code.

The other option is:

All events that a single click can produce are Undoable and are undone once an asociated double click event arrives .

Implementing Undo is an interesting topic, but for simplicity I will give a very basic example instead:

import javafx.fxml.FXML;
import javafx.scene.input.MouseEvent;

class SomeController {

    private static final long MAX_MULTICLICK_INTERVAL = 200; //the milliseconds delay
    private long lastSingleClickTime = 0;

    private int singleClickCounter = 0, doubleClickCounter = 0;

    private void singleClick(MouseEvent event) {
        singleClickCounter++;
    }

    private void undoSingleClick(MouseEvent event) {
        singleClickCounter--;
    }

    private void doubleClick(MouseEvent event) {
        doubleClickCounter++;
    }

    @FXML
    private void onMouseClicked(MouseEvent event) {
        if (event.getClickCount() == 2) {
            if (System.currentTimeMillis() <= lastSingleClickTime + MAX_MULTICLICK_INTERVAL) {
                undoSingleClick(event);
                lastSingleClickTime = 0; //if another double-click arrived we don't want to undo anything
            }
            doubleClick(event);
        } else if (event.getClickCount() == 1) {
            lastSingleClickTime = System.currentTimeMillis(); //in AWT use the event.getWhen() method instead
            singleClick(event);
        } // else: might swallow button clicks with clickCount outside 1 and 2 which is ok for me
        System.out.printf("Single clicks: %d, double clicks: %d\n", singleClickCounter, doubleClickCounter);
    }
}

Note that primary, secondary and middle button events are mixed for simplicity here. You should track a lastSingleClickTime for each of the buttons or limit the processing to the primary button only, since that is usually the only button using double-clicks anyway.

With a data model implementing Undo one would remember the Action the single click fired (let that be a class having a run() and undo() method doing opposite things) and call .undo() on that Action instance when the double click event arrived. There are pitfalls of course. But that would be a long chapter.