RFR: 8165749: java.lang.RuntimeException: dndGesture.dragboard is null in dragDrop

[Kevin Rushforth]

On Wed, 6 Jan 2021 16:20:47 GMT, Jose Pereda <jpereda at openjdk.org> wrote:

> As commented in the JBS issue, there is one single `dndGesture` object in `Scene`, that can be instantiated from three different ways: 
> 
> - DropTargetListener, on dragEnter 
> - DragGestureListener, on dragGestureRecognized or 
> - MouseHandler, processing a right mouse click (these two are mutually exclusive).  
> 
> This PR prevents that, for two almost simultaneous drag events (for instance via mouse and touchpad), the `dndGesture` for the last of these events gets initialized again, losing all existing drag info (`dndGesture.dragboard`) that was added to the first one, avoiding the RTE.
> 
> The existing manual test [DndTest](https://github.com/openjdk/jfx/blob/master/tests/manual/dnd/DndTest.java) has been used on MacOS to verify the PR.

modules/javafx.graphics/src/main/java/javafx/scene/Scene.java line 3788:

> 3786:                         //old gesture ended and new one started
> 3787:                         gestureStarted = true;
> 3788:                         if (!PLATFORM_DRAG_GESTURE_INITIATION && Scene.this.dndGesture == null) {

This will prevent the creation of the new `DndGesture`, but we will still clear the PDR targets. Have you confirmed that this is the desired behavior? It seems reasonable, since we also clear it on a mouse move, but wanted to get your take on it.

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PR: https://git.openjdk.java.net/jfx/pull/372