When IsFilteringEnabled property of RadComboBox is set to True the auto completion ability of RadComboBox is not available - thus no auto completion could be provided while that property is set to True.
However, what you could also consider is using RadAutoCompleteBox
instead of RadComboBox - it provides many helpful features such as creating custom filtering behavior. Please, check the Silverlight online demos
(they are identical with the ones for WPF) and SDK examples
of the control.
We hope this will help you.
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