Add a class to Dropzones on dragStart?

[mdrx-io]

Please correct me if you've already built in this feature to the API in some form. But I would like to be able to add a class to acceptable Dropzones for a Draggable on dragStart. The goal being to give the user hints as to where she might be able to drop a Draggable (like a border-color modification around the Dropzone element).

[marcojakob]

It isn't built in because the Dropzone doesn't have a reference to all possible Draggables.

But you can do it by listening to the onDragStart and onDragEnd events:

Draggable draggable = new Draggable(draggableElements, 
    avatarHandler: new AvatarHandler.clone());
Dropzone dropzone = new Dropzone(dropzoneElements);

// Add class when dragging starts and remove it when dragging ends.
draggable.onDragStart.listen((_) {
  dropzoneElements.classes.add('drop-here');
});

draggable.onDragEnd.listen((_) {
  dropzoneElements.classes.remove('drop-here');
});