TreeLayout DoLayout

I have some question.

The ExternalObjectsDropped event call the TreeLayout.DoLayout method ?

after palette -> diagram drag & drop execute, automatically method call ??

The Diagram.ExternalObjectsDropped event is raised when the user successfully drag-and-drops from one Diagram to another Diagram.

Every transaction causes all invalid layouts to be performed. But no event inherently requires a layout to happen. But what you describe is common.

i don’t understand

why TreeLayout.DoLayout method called?? after ExternalObjectesDropped ??

The LayoutManager decides whether a layout needs to be performed again automatically at the end of a transaction.

Adding or removing nodes or links will normally invalidate the layout.