PRB: GetActiveView Returns NULL for an MDI Frame Window

   CMDIFrameWnd *pFrame = (CMDIFrameWnd *)AfxGetApp()->m_pMainWnd;
   // Get the active MDI child window.
   CMDIChildWnd *pChild =
                  (CMDIChildWnd *) pFrame->GetActiveFrame();
   /* or CMDIChildWnd *pChild =
                  pFrame->MDIGetActive();
   */ 
   // Get the active view attached to the active MDI child window.
   CMyView *pView = (CMyView *) pChild->GetActiveView();
				

MORE INFORMATION

The client area of the MDI frame window is covered by the client window referred to as the MDICLIENT, also known as the Workspace. This client window in turn contains zero or more child windows, each of which can display a view, as in this diagram:

                    ---------------------------
                   |      Frame Window         |  ---> CMDIFrameWnd
                   | (main application window) |
                    ---------------------------
                             |
                    --------------------
                   |   Client Window    |  ---> MDICLIENT window class
                   | (no view attached) |
                    --------------------
                             |
         -----------------------------------------------------------
         |                            |
 ---------------------      --------------------
|   Child Window 1    |    |   Child Window 2   |  ---> CMDIChildWnd
| (one or more views) |    | (one or more views |
 ---------------------      --------------------
				

As illustrated in this diagram, the MDI frame window does not have a view directly associated with it. The views are actually associated with the MDI child windows.

Therefore, calling the GetActiveView() function for an MDI main frame window returns NULL, implying that there is no view directly associated with MDICLIENT. The active view in an MDI application can be obtained by first finding the active MDI child window and then finding the active view for that child window as outlined in the Resolution section of this article.