Cancelling ListBox SelectedIndexChange Event

You cannot cancel it.

What I did just a couple of days ago was to have a variable with the latest selected index. Then when the event fires, you ask the user if he wants to save, this is done in the eventhandler. If the user selected "Cancel" you change the id again.

The problem is that this will make the event fire once again. So what i've used is a bool just saying "Inhibit". And at the top of the eventhandler I have:

if(Inhibit)
   return;

Then below this where you ask the question you do something like this:

DialogResult result = MessageBox.Show("yadadadad", yadada cancel etc);
if(result == DialogResult.Cancel){
   Inhibit = true; //Make sure that the event does not fire again
   list.SelectedIndex = LastSelectedIndex; //your variable
   Inhibit = false; //Enable the event again
}
LastSelectedIndex = list.SelectedIndex; // Save latest index.

This is exactly @Oskar Kjellin 's method, but with a twist. That is, one variable less and with a selected index changed event that really behaves like a selected index changed event. I often wonder why is selected index changed event getting fired even if I click on the exact same selected item. Here it doesn't. Yes it's a deviation, so be doubly sure if you want this to be there.

    int _selIndex = -1;
    private void listBox1_SelectedIndexChanged(object sender, EventArgs e)
    {
        if (listBox1.SelectedIndex == _selIndex)
            return;

        if (MessageBox.Show("") == DialogResult.Cancel)
        {
            listBox1.SelectedIndex = _selIndex;
            return;
        }

        _selIndex = listBox1.SelectedIndex;
        // and the remaining part of the code, what needs to happen when selected index changed happens
    }