SAMPLE: VSWAP32 Demos Multiple-View Switching in SDI

Last reviewed: July 31, 1997
Article ID: Q141334

The information in this article applies to:

The Microsoft Foundation Classes (MFC) included with: Microsoft Visual C++, 32-bit Edition, version 4.0, 4.1, 4.2, 5.0

SUMMARY

VSWAP32 demonstrates methods of switching between multiple views on a single document in a single-document interface (SDI) application. VSWAP32 displays two form views and a normal view that displays the list of data collected in the two form views.

NOTE: This is the 32-bit version of this sample. There is also a 16-bit version available called VSWAP.EXE.

This sample application demonstrates using DDX/DDV (dialog data exchange/dialog data validation), with correct document updating and data validation when switching between views. It also correctly catches unsaved/unvalidated data when the application is closed.

The following file is available for download from the Microsoft Software Library:

 ~ Vswap32.exe (size: 44150 bytes)

For more information about downloading files from the Microsoft Software Library, please see the following article in the Microsoft Knowledge Base:

   ARTICLE-ID: Q119591
   TITLE     : How to Obtain Microsoft Support Files from Online Services

After downloading the file, use the following command to extract the sample and build the appropriate directory structure:

   VSWAP32.EXE -d

MORE INFORMATION

The most important implementations of this are in:

    CVswapApp::InitInstance
    CVswapApp::SwitchView
    CVswapApp::SaveActiveViewsData

The standard InitInstance code creates an initial document template, document, and view during the call to ProcessShellCommand. The code added to the end of InitInstance creates the view objects for the extra views used in this application and stores their pointers in a CVswapApp member array. It then cycles through a loop which creates the windows for the view objects. Each view window is created with a unique child window ID and a CCreateContext object that associates each view with the same CDocument object, which was created by ProcessShellCommand. Finally, the sample code triggers the OnInitialUpdate for the extra views.

In this sample, both views persist for the lifetime of the application; however, the application could create the new view dynamically.

The SwitchView function created in this sample swaps the current view with a previously hidden view. It accomplishes this by first switching their child window IDs. This step is necessary because MFC relies on the standard view pane having the child window ID of AFX_IDW_PANE_FIRST. The rest of the code hides the current view and tells MFC to repaint and begin using the new view.

The SaveActiveViewsData is used to save the information from the active view to the document object. It is called by SwitchView whenever a view is switched. SaveActiveViewsData subsequently calls SetToDoc, which actually updates the data from the form view to the document by using MFC's DDX/DDV mechanisms in DoDataExchange.

Sample Code

      The SwitchView function is included here as a reference.

      CView* CVswapApp::SwitchView( UINT nIndex )
      {
          ASSERT( nIndex >=0 && nIndex < NUMVIEWS );

          CView* pNewView = m_pViews[nIndex];

          CView* pActiveView =
          ((CFrameWnd*) m_pMainWnd)->GetActiveView();

          if ( !pActiveView )    // No currently active view.
              return NULL;

          if ( pNewView == pActiveView )    // Already there.
              return pActiveView;

          // Update Doc's data if needed
          // Don't change view if data validation fails
          if ( ! SaveActiveViewsData() )
          {
              return pActiveView;
          }

          m_nCurView = nIndex;    // Store the new current view's index.

          // Exchange view window ID's so RecalcLayout() works.
          UINT temp = ::GetWindowLong(pActiveView->m_hWnd, GWL_ID);
          ::SetWindowLong(pActiveView->m_hWnd, GWL_ID,
                ::GetWindowLong(pNewView->m_hWnd, GWL_ID));
          ::SetWindowLong(pNewView->m_hWnd, GWL_ID, temp);

          // Display and update the new current view - hide the old one.
          pActiveView->ShowWindow(SW_HIDE);
          pNewView->ShowWindow(SW_SHOW);
          ((CFrameWnd*) m_pMainWnd)->SetActiveView(pNewView);
          ((CFrameWnd*) m_pMainWnd)->RecalcLayout();
          pNewView->Invalidate();
          return pActiveView;
      }

REFERENCES

For other examples of applications that switch views, please refer to the following samples:

   COLLECT   (SDI)
   ENROLL    (SDI)
   VWRPLC32  (MDI)
   SPLIT32   (Splitter).

For more information on DDX and DDV routines, please see Technical Note 26: DDX and DDV Routines in the Microsoft Development Library.

Keywords          : MfcDocView kbprg kbsample kbfile
Technology        : kbMfc
Version           : 4.0 4.1 4.2 5.0
Platform          : NT WINDOWS
Solution Type     : kbcode

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Last reviewed: July 31, 1997
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