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. ------------- Commit messages: - Only instantiate dndGesture if previous drag gestures have finished Changes: https://git.openjdk.java.net/jfx/pull/372/files Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=372&range=00 Issue: https://bugs.openjdk.java.net/browse/JDK-8165749 Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod Patch: https://git.openjdk.java.net/jfx/pull/372.diff Fetch: git fetch https://git.openjdk.java.net/jfx pull/372/head:pull/372 PR: https://git.openjdk.java.net/jfx/pull/372
