C# Form.Close vs Form.Dispose

This forum on MSDN tells you.

Form.Close() sends the proper Windows messages to shut down the win32 window. During that process, if the form was not shown modally, Dispose is called on the form. Disposing the form frees up the unmanaged resources that the form is holding onto.

If you do a form1.Show() or Application.Run(new Form1()), Dispose will be called when Close() is called.

However, if you do form1.ShowDialog() to show the form modally, the form will not be disposed, and you'll need to call form1.Dispose() yourself. I believe this is the only time you should worry about disposing the form yourself.

As a general rule, I'd always advocate explicitly calling the Dispose method for any class that offers it, either by calling the method directly or wrapping in a "using" block.

Most often, classes that implement IDisposible do so because they wrap some unmanaged resource that needs to be freed. While these classes should have finalizers that act as a safeguard, calling Dispose will help free that memory earlier and with lower overhead.

In the case of the Form object, as the link fro Kyra noted, the Close method is documented to invoke Dispose on your behalf so you need not do so explicitly. However, to me, that has always felt like relying on an implementaion detail. I prefer to always call both Close and Dispose for classes that implement them, to guard against implementation changes/errors and for the sake of being clear. A properly implemented Dispose method should be safe to invoke multiple times.

Not calling Close probably bypasses sending a bunch of Win32 messages which one would think are somewhat important though I couldn't specifically tell you why...

Close has the benefit of raising events (that can be cancelled) such that an outsider (to the form) could watch for FormClosing and FormClosed in order to react accordingly.

I'm not clear whether FormClosing and/or FormClosed are raised if you simply dispose the form but I'll leave that to you to experiment with.