As I do not have details on your specific usage scenario , here are some general thoughts :
RadTreeListiView has an internal state preservation logic - a cache that stores /restores the expand state of the items . This logic relies on the item , meaning the state is kept for data items rather than for UI elements.
If you change/update the item, the new instance is not present in the cache yet , therefore it gets the default collapsed state.
This means you will need to implement an external mechanism ( e.g. a dictionary or a hashtable ) to store the state and set it after updates.
In case you can show me your project , I will be glad to have a look at it and give some additional assistance on implementing the above suggested approach .
All the best,
the Telerik team
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