Hi there, In my opinion, there might be some reasons as to why the SelectedIndexChanged event does not fire. In the 'Process postback data' phase of the Control Execution Lifecycle, the LoadPostData method will be running. This method basically does a comparison between the current selected item with the posted value. Depending on the returned value of the method, the SelectedIndexChanged will be raised or not in the next phase ('Send postback change notifications'). So I think that there may be no data at all in the Items of the control when the LoadPostData is running, and the event is not raised. Another reason might be when the SelectedIndexChanged event fires in the 'Send postback change notifications' phase, there is no handler registered for this event by that time, so you might think that the event does not fire. For more information, I'd recommend you to read some documents below: Control Execution Lifecycle[^] Processing Postback Data[^] Adding Controls to a Web Forms Page Programmatically[^]