ComboBox SelectedIndexChanged event: how to get the previously selected index?

Question

I have a user control which has a ComboBox and a SelectedIndexChanged event handler. In the event handler, I need to be able to tell what was the previously selected index.

Answer 1

There is nothing built in, you will need to listen for this event and keep track in an instance variable.

Use -1 as an uninitialized "last index", so on first pass you set it but don't use it. Subsequent passes you use it and set it.

You could always do this using a derived ComboBox class of your own and override OnSelectedIndexChanged and expose a PreviousSelectedIndex property. This way, it wouldn't be tightly coupled to the form. Alternatively, as you can do this using events, its also eligible for implementation as an extender provider.