Getting the mouse drag release event on a canvas ?

[Joe Smithh]

I have scene consisting of a single canvas. I'm using the canvas context to draw graphics on. I'm tracking the mouse location for input. Everything is working fine but I can't get the mouse drag release event to respond. I'm using the mouse press / release events to track button pushes. The standard press / release mouse events respond fine but after performing a drag the mouse drag release never happens.



Here is the function for my mouse events. It should print "drag release" but the mouse drag release event isn't happening.

private void startMouseInput(){

       

        scene.addEventFilter(MouseEvent.MOUSE_MOVED, new EventHandler<MouseEvent>() {

                   @Override

                   public void handle(MouseEvent event) {

                   mouse.lastLocation.set( event.getX() , event.getSceneY() );

                   event.consume();

                   }

         });

 

        scene.addEventFilter(MouseEvent.DRAG_DETECTED , new EventHandler<MouseEvent>() {

                   @Override

                   public void handle(MouseEvent event) {

         

                    scene.setCursor(Cursor.DEFAULT);

                    Dragboard db = scene.startDragAndDrop(TransferMode.ANY);

                    /* Put a string on a dragboard */

                    ClipboardContent content = new ClipboardContent();

                    content.putString("test");

                    db.setContent(content);

                    //mouse.lastLocation.set( event.getX() , event.getSceneY() );

                    scene.startFullDrag();

         

                    event.consume();

         

         

                   }

         });

 

        scene.addEventFilter(DragEvent.DRAG_OVER, new EventHandler<DragEvent>() {

                   @Override

                   public void handle(DragEvent event) {

                   mouse.lastLocation.set( event.getX() , event.getSceneY() );

                   event.consume();

                   }

        });

       

        scene.addEventFilter(MouseDragEvent.MOUSE_DRAG_RELEASED, new EventHandler<MouseDragEvent>() {

                   @Override

                   public void handle(MouseDragEvent event) {

                   System.out.println("drag release");

                   mouse.lastLocation.set( event.getX() , event.getSceneY() );

                   event.consume();

                   }

        });

       

        scene.addEventFilter(ScrollEvent.SCROLL, new EventHandler<ScrollEvent>() {

            @Override

            public void handle(ScrollEvent event) {

               for (MouseKey key : mouse.getKeys()) {

                         if (key.getTrigger() == MouseKeyTrigger.WHEEL){

                             ScrollEvent evt = (ScrollEvent)event;

                             key.setDelta(evt.getDeltaY());

                             mouse.fireMouseWheel( evt.getDeltaX() , evt.getDeltaY() );

                         }

               }

               event.consume();

            }

    });

        

         scene.addEventFilter(MouseEvent.MOUSE_PRESSED, new EventHandler<MouseEvent>() {

                   @Override

                   public void handle(MouseEvent event) {

                     for (MouseKey key : mouse.getKeys()){

                         if (event.getButton() ==  MouseButton.PRIMARY){

                             if (key.getTrigger() == MouseKeyTrigger.BUTTON1){

                                  key.triggered(true);

                             }

                         } else if (event.getButton() ==  MouseButton.SECONDARY){

                             if (key.getTrigger() == MouseKeyTrigger.BUTTON2){

                                  key.triggered(true);

                             }

                         } else if (event.getButton() ==  MouseButton.MIDDLE){

                             if (key.getTrigger() == MouseKeyTrigger.BUTTON3){

                                  key.triggered(true);

                             }

                         }

                     }

                     event.consume();

                   }

         });

        

         scene.addEventFilter(MouseEvent.MOUSE_RELEASED, new EventHandler<MouseEvent>() {

         @Override public void handle(MouseEvent event) {

                    for (MouseKey key : mouse.getKeys()){

                         if (event.getButton() ==  MouseButton.PRIMARY){

                             if (key.getTrigger() == MouseKeyTrigger.BUTTON1){

                                  key.triggered(false);

                             }

                         } else if (event.getButton() ==  MouseButton.SECONDARY){

                             if (key.getTrigger() == MouseKeyTrigger.BUTTON2){

                                  key.triggered(false);

                             }

                         } else if (event.getButton() ==  MouseButton.MIDDLE){

                             if (key.getTrigger() == MouseKeyTrigger.BUTTON3){

                                  key.triggered(false);

                             }

                         }

                         event.consume();

                  }

      }

    });

        

    }

[John Damien Smith]

You are filtering MOUSE_RELEASED events and consuming them.  My guess is that this may cause MOUSE_DRAG_RELEASED events not to be triggered.  (I don't know for sure as I didn't try executing your code snippet, but it just a guess).  I recommend not consuming events unless you know you need to consume them as consuming events (especially in filters) can prevent standard event handlers from being executed.  If you capture events instead of letting them bubble then you run the risk of disabling default functionality (sometimes you want to disable default functionality, which is why filters are there, but most of the time you don't, which is why they are not often used).  

For background see the info on bubbling and filtering at: https://docs.oracle.com/javase/8/javafx/events-tutorial/processing.htm

I'm not sure why you use event filters rather than event handlers as the Oracle drag and drop tutorial recommends:
 https://docs.oracle.com/javase/8/javafx/events-tutorial/drag-drop.htm#CHDJFJDH
It shouldn't really matter either way in this case, but I would think using event handlers would be generally preferred.

It is also odd that you are setting filters on the scene.  If you are working a user interacting with a drawing on a canvas, then setting your event filters or handlers on the canvas itself rather than the scene would seem to be preferable.  If the scene contains other widgets such as tool drawing tool icons and controls, then setting an overall event filter on the scene may prevent those drawing tools and icons from receiving events that they would be expected to get to allow their actions to work.

[John Damien Smith]

Crossposts:
 https://community.oracle.com/thread/4030544
 http://stackoverflow.com/questions/43038567/javafx-fire-mouse-release-event-after-drag-over
Please note the JavaRanch policy on cross posts, thanks:
 https://coderanch.com/wiki/660346/Forthright-Cross-Posting-Sites

[Joe Smithh]

John Damien Smith wrote:You are filtering MOUSE_RELEASED events and consuming them.  My guess is that this may cause MOUSE_DRAG_RELEASED events not to be triggered.  (I don't know for sure as I didn't try executing your code snippet, but it just a guess).  I recommend not consuming events unless you know you need to consume them as consuming events (especially in filters) can prevent standard event handlers from being executed.  If you capture events instead of letting them bubble then you run the risk of disabling default functionality (sometimes you want to disable default functionality, which is why filters are there, but most of the time you don't, which is why they are not often used).  

For background see the info on bubbling and filtering at: https://docs.oracle.com/javase/8/javafx/events-tutorial/processing.htm

I'm not sure why you use event filters rather than event handlers as the Oracle drag and drop tutorial recommends:
 https://docs.oracle.com/javase/8/javafx/events-tutorial/drag-drop.htm#CHDJFJDH
It shouldn't really matter either way in this case, but I would think using event handlers would be generally preferred.

It is also odd that you are setting filters on the scene.  If you are working a user interacting with a drawing on a canvas, then setting your event filters or handlers on the canvas itself rather than the scene would seem to be preferable.  If the scene contains other widgets such as tool drawing tool icons and controls, then setting an overall event filter on the scene may prevent those drawing tools and icons from receiving events that they would be expected to get to allow their actions to work.

Okay , thanks for the advice. I got rid of the consume events which helped because that was causing other nodes to not respond to events. What the problem seems to be is that when you drag a control you need to have a target for the drop. What I wanted to do was create a control that could respond to its own drag event but it looks like that may not be possible. Ultimately what I did was call the drag detect on the canvas then use the scene as the drag drop target. Basically this works. Where canvas is the draggable control and scene is target. I'm not actually moving the canvas I'm just using it to get the mouse events.

private void startMouseInput(){
        
        // Add mouse event handlers for the source
		core.canvas.setOnMousePressed(new EventHandler <MouseEvent>()
		{
            public void handle(MouseEvent event)
            {
            	core.canvas.setMouseTransparent(true);
            	//writelog("Event on Source: mouse pressed");
            	event.setDragDetect(true);
            }
        });

		core.canvas.setOnMouseReleased(new EventHandler <MouseEvent>()
		{
            public void handle(MouseEvent event)
            {
            	core.canvas.setMouseTransparent(false);
            	//writelog("Event on Source: mouse released");
            }
        });

		core.canvas.setOnMouseDragged(new EventHandler <MouseEvent>()
		{
            public void handle(MouseEvent event)
            {
            	//writelog("Event on Source: mouse dragged");
                   core.mouse.lastLocation.set( event.getX() , event.getSceneY() );
            	event.setDragDetect(false);
            }
        });

		core.canvas.setOnDragDetected(new EventHandler <MouseEvent>()
		{
            public void handle(MouseEvent event)
            {
            	core.canvas.startFullDrag();
            	//writelog("Event on Source: drag detected");
            }
        });

		// Add mouse event handlers for the target
		core.scene.setOnMouseDragEntered(new EventHandler <MouseDragEvent>()
		{
            public void handle(MouseDragEvent event)
            {
            	//writelog("Event on Target: mouse dragged");
            }
        });

		core.scene.setOnMouseDragOver(new EventHandler <MouseDragEvent>()
		{
            public void handle(MouseDragEvent event)
            {
            	//writelog("Event on Target: mouse drag over");
            }
        });

		core.scene.setOnMouseDragReleased(new EventHandler <MouseDragEvent>()
		{
            public void handle(MouseDragEvent event)
            {
                //System.out.println("drag released");
            	//targetFld.setText(sourceFld.getSelectedText());
            	//writelog("Event on Target: mouse drag released");
            }
        });

		core.scene.setOnMouseDragExited(new EventHandler <MouseDragEvent>()
		{
            public void handle(MouseDragEvent event)
            {
            	//writelog("Event on Target: mouse drag exited");
            }
        });
         
                core.scene.addEventFilter(ScrollEvent.SCROLL, new EventHandler<ScrollEvent>() {
            @Override
            public void handle(ScrollEvent event) {
               for (MouseKey key : core.mouse.getKeys()) {
                         if (key.getTrigger() == MouseKeyTrigger.WHEEL){
                             ScrollEvent evt = (ScrollEvent)event;
                             key.setDelta(evt.getDeltaY());
                             core.mouse.fireMouseWheel( evt.getDeltaX() , evt.getDeltaY() );
                         }
               }
               //event.consume();
            }
    });
                
                core.scene.addEventFilter(MouseEvent.MOUSE_MOVED, new EventHandler<MouseEvent>() {
                   @Override 
                   public void handle(MouseEvent event) {
                   core.mouse.lastLocation.set( event.getX() , event.getSceneY() );
                   //event.consume();
                   }
         });
            
                core.scene.addEventFilter(MouseEvent.MOUSE_PRESSED, new EventHandler<MouseEvent>() {
                   @Override 
                   public void handle(MouseEvent event) {
                       //System.out.println("mouse pressed");
                     for (MouseKey key : core.mouse.getKeys()){
                         if (event.getButton() ==  MouseButton.PRIMARY){
                             if (key.getTrigger() == MouseKeyTrigger.BUTTON1){
                                  key.triggered(true);
                             }
                         } else if (event.getButton() ==  MouseButton.SECONDARY){
                             if (key.getTrigger() == MouseKeyTrigger.BUTTON2){
                                  key.triggered(true);
                             }
                         } else if (event.getButton() ==  MouseButton.MIDDLE){
                             if (key.getTrigger() == MouseKeyTrigger.BUTTON3){
                                  key.triggered(true);
                             }
                         }
                     }
                     //event.consume();
                   }
         });
         
         core.scene.addEventFilter(MouseEvent.MOUSE_RELEASED, new EventHandler<MouseEvent>() {
         @Override public void handle(MouseEvent event) {
                    for (MouseKey key : core.mouse.getKeys()){
                         if (event.getButton() ==  MouseButton.PRIMARY){
                             if (key.getTrigger() == MouseKeyTrigger.BUTTON1){
                                  key.triggered(false);
                             }
                         } else if (event.getButton() ==  MouseButton.SECONDARY){
                             if (key.getTrigger() == MouseKeyTrigger.BUTTON2){
                                  key.triggered(false);
                             }
                         } else if (event.getButton() ==  MouseButton.MIDDLE){
                             if (key.getTrigger() == MouseKeyTrigger.BUTTON3){
                                  key.triggered(false);
                             }
                         }
                         //event.consume();
                  }
      }
    });
         
    }