Checkbox + Listbox selection

I have one checkbox -开发者_Go百科 when its checked all the items in listbox are selected. I want when all the items are selected with the checkbox and i click on some of the items - all other items to be unckecked and the item I clicked on to stay checked - how to do that?

You have to do this manually: uncheck all items and check the one you clicked.

However, I don't know if it's possible that the user can select more then one item. If so, you have to keep in mind that when the checkbox isn't checked, you don't have to uncheck the other items in the listbox.