FAQ: Cannot re-show a WinForms form that's been closed

This one comes up in the forums at least once a week. The scenario is where someone shows a form, closes it while retaining the handle, and then tries to show it again by calling Show or ShowDialog on the closed form. This throws an exception that says the object has been disposed.

Here’s my standard answer. You cannot re-show a form once it’s closed because the underlying window is destroyed. You can hide the form and then re-show it as required thereby reusing the same form instance.

Alternatively, for modal dialogs, instantiate a local form variable and call ShowDialog on that. So each time it’s a new form. And this way you don’t need to keep the form in memory all the time, specially if it’s an options dialog that’s rarely brought up.