What is the lifetime of a CWnd obtained from CWnd::FromHandle?

Question

According to msdn, when I get a CWnd* with CWnd::FromHandle,

The pointer may be temporary and should not be stored for later use.

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Answer 1

FromHandle is basically used for getting a transient reference to an already existing window object. MFC stores these references in an internal structure called a temporary handle map (a handle map is a map of Windows HWNDs to MFC CWnd objects used by MFC to make Win32 calls to manipulate the actual Windows window the MFC object corresponds to). In order to avoid the number of objects in this structure from growing beyond all bounds, items are deleted from the handle map during MFC's idle loop processing.

As you may have guessed, there is also a permanent handle map that won't have this automatic clean up behavior. If you need to get a CWnd object that doesn't put its HWND reference in the temporary handle map you can call FromHandlePermanent().

-Ron