Using header and content templates of the RadPanelItems you can directly access the needed control meaning that simply typing the id of the control directly in the Page_Load event is identical to typing the below lines of code (you can also refer to the attached image):
var menu = panelbar1.Items.Header.FindControl(
var menuu = panelbar1.Items.FindControl(
However, you can not use the above mentioned approach when you have an ItemTemplate.
Considering your other question with databinding can you please elaborate a bit more since I am not quite sure that I completely understand your question?
the Telerik team
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