Hi,

That ID is actually the item's ZIndex. The control always keeps the ZIndices as integers in the range 0 .. n-1 , where n is the number of items in the diagram. So, this might not work as a general-purpose unique ID, because if you delete some items or call the setZIndex method, the index of other items will change automatically. Though it is ok as a one-time ID during serialization time.

I hope that helps,
Stoyan

Deleting a node at some Z position will shift the nodes at higher Z one position down, and change their Z-index, so I would not use that index as a unique ID.

You could keep a global long-int counter as a value of the Diagram's Tag property, assign it to each item's Tag when a new item is created, and increment it. Then you'll be sure that the item's Tag is a unique value for this diagram. Though you might have to take care of copy/paste operations if you allow them. Also if you expect your application to be used in many millennia ahead, you might have to add a provision for when the counter reaches Long.MAX_VALUE

I hope that helps,
Stoyan