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Persisting Graphics on a Form

You'll often use the techniques discussed in this hour to draw to a form. However, you may recall from earlier hours that when you draw to a form (actually, you draw to a Graphics object that references a form), the things that you draw aren't persisted; the next time the form paints itself, the drawn elements will disappear. If the user minimizes the form or obscures the form with another window, for example, the next time the form is painted, it will be missing any and all drawn elements that were obscured. You can use a couple of approaches to deal with this behavior:

• Place all code that draws to the form in the form's Paint event.

• Draw to a memory bitmap and copy the contents of the memory bitmap to the form in ...