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… can anyone point me in the right direction?

private void cboTargetMode_SelectedIndexChanged(object sender, EventArgs e)
{
    // need to get the previously selected index and do some handling here...
    // ... some handler code here ...


    switch (cboTargetMode.SelectedIndex)
    {
        case 1:  // ..... some code here...
            break;
        case 2:  // ..... some code here...
            break;
        case 3:  // ..... some code here...
            break;
        default: // ..... some code here...
            break;
    }
}

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.