Hi PEIYANG ,
The RadTreeView generates its containers - the RadTreeViewitems when they are:
1) Root Level Items
2) Non-Root Item but their parent is Expanded
I guess you use TriState mode of the RadTreeView with setting the IsInTriStateMode = True. If so, when you check a root level Item which has never been expanded, only it will be in the CheckedItems Collection. In other words its children cannot be in the CheckedItems since they are not generated yet.
Could you please elaborate more on your scenario? It's not a good idea to use the CheckedItems collection because it has some known issues.
the Telerik team
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