How to count only checked items in CheckedListBox dynamically while the user is checking boxes?

Question

I have a CheckedListBox control on my windows form application, which gives a list of items to select from. I want to count and show only checked (not selected) items while the user is still checking them. I mean count as you check them.

I have tried to use ItemCheck event and CheckedListBox.CheckedItems.Count but the problem is that it counts every other click even if the item is unchecked. When I check something it counts and if I unchecked it again, it counts that too.

I think it has to do with the remark given on MSDN "The check state is not updated until after the ItemCheck event occurs." I do not completely understand the problem here.

Thank you.

Answer 1

The ItemCheckEventArgs parameter has the Property (NewValue) which tells you whether the change is a check, uncheck or neither.

If CheckedItems.Count is not updated until after the event fires (which is what I'm understanding from that remark) - then you can add that count, and see whether the ItemChecckEventArgs is a check (+1) or an uncheck (-1) and you can get the correct total.

(Unless I'm understanding the remark wrongly, its very vague).

Answer 2

Haedrian answered this correctly, but i think raw code goes a long ways too. So here's the C# code:

private void CheckedListBox_ItemCheck(Object sender, ItemCheckEventArgs e)
{
    int sCount = checkedListBox.CheckedItems.Count;
    if (e.NewValue == CheckState.Checked  ) { ++sCount; }
    if (e.NewValue == CheckState.Unchecked) { --sCount; }
    // now sCount is count of selected items in checkedListBox.
}

I had the same issue, and this question and answer gave me the solution. Thanks for the question and already existing answers!