You can use the ItemPrepared
event to know when a RadTreeViewItem is prepared into the viewport. By preparing I mean, creating of the container or changing its data context. By default the UI virtualization will re-use the containers so most of the time they won't be unloaded.
Currently, there is no event for the moment when the item context is changed (unloaded). It is possible to use the IsVisibleChanged and Unloaded event of the RadTreeViewItem. The Unloaded event will be fired when the container is no longer needed, therefore it is no longer used. And the IsVisibleChanged will be fired in some cases when the container is recycled.
If you tell me what exactly you want to achieve I could think of a possible solution for your scenario.
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