I am not sure I managed to understand your requirements correctly. Once after you insert a RadDocking in the RadTabItem, do you need to insert other RadDocking controls or you mean RadPanes? On the other hand, what do you mean exactly with "How i can Insert and data On tabitem1 that will not lose" ? Do you mean that you don't want your RadTabItems to re-load on every SelectionChanged that is made ? If so, you can set the IsContentPreserved property to true.
Thank you in advance for your cooperation.
the Telerik team
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