We drag node from first one to second.
When we drop item to target tree we need to call request to change data model on the server (in database). And only after getting response we need to do some changes in target tree.
But when we dropped item to target tree, ExtJS whether adds new node to target or shows animated flight of item to source tree (if we said 'cancel drop'). The both cases is not convenient. Nothing has to happen with trees until we get response from server (e. g. after 10 seconds).
I told you about the same in all posts. In this handler I call request. But this method life cycle is finished before response comes from server. Dropping finished. And whether new node is created in target tree (if I don't cancel drop) or drop is canceled (if I do).