Thank you for this question.
You should first wrap the user control inside RadHostItem
and after that you will be able to add it into CommandBarHostItem
. Please consider the following code snippet:
RadHostItem hostedButton =
//this line set the size
.commandBarHostItem1.HostedItem = hostedButton;
I hope this helps.Don't hesitate to contact us if you have other questions.
the Telerik team