Hello ricky wu,
with RadDocking is not supported. You should manually create RadPanes and add them to the RadPaneGroup.Items collection.
All the best,
the Telerik team
Do you want to have your say when we set our development plans? Do you want to know when a feature you care about is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items.