When you use RadComboBox with CheckBoxes feature enabled - the user should not be able to type in control
. The CheckBoxes feature sets the text automatically when a checkbox is checked or unchecked.
Additionally - the OnClientItemsRequested event is used only if you enable RadComboBox Load On Demand feature.
As my colleague has already mentioned - the simultaneous usage of Load On Demand and CheckBoxes is not supported.
I am suggesting you test the RadComboBox behaviour under different configurations with this online demo
All the best,
the Telerik team
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to their blog feed