Thank you for your question.
After you check that the ItemsSource contains only 1 item, you could set the SelectedIndex
property of the ComboBox to that item. For more information you can refer to this help article: http://www.telerik.com/help/silverlight/radcombobox-features-selection.html
Hope this information helps. If you have any other questions please let us know.
the Telerik team
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