C++--在单文档的应用程序增加多个视图

在mfc的单文档的应用程序(Application)设计时，一般是一种文档(Documnet)对应一种视图(View) 。然而在有些时候我需要一种文档用多种视图来展现，具体步骤如下：

我们有两个假设

• CMyWinApp是该程序的应用程序,并声明和定义在MYWINAPP.H和MYWINAPP.CPP文件中.
• CNewView是从CView上继承的视图类, 并声明和定义在NEWVIEW.H and NEWVIEW.CPP文件中.
  1.修改应用程序类(Application Class);在MYWINAPP.H加入如下声明
  CView* m_pOldView;
  CView* m_pNewView;
  CView* SwitchView( );
   m_pOldView 和m_pNewView分别指向当前的视图类(新建程序时自动创建的一个视图类)和即将创建的新的视图类,SwitchView函数用于相应用户视图切换操作，具体实现参见下面的步骤。
  在MYWINAPP.CPP文件中加入
  #include <AFXPRIV.H>
  2.创建和修改新的视图类 (View Class)选择菜单的“New Class”创建新的视图类，并将构造函数和析构函数的访问类型由protected改成public，这样用于动态创建视图。完成后保存文件。
  3.创建和绑定新视图(View)
  为了创建和绑定新视图，我们需要修改应用程序类的InitInstance函数，在ProcessShellCommand后面添加如下代码并保存：
  ...
  CView* pActiveView = ((CFrameWnd*) m_pMainWnd)->GetActiveView();
  m_pOldView = pActiveView;
  m_pNewView = (CView*) new CNewView;
  
  CDocument* pCurrentDoc = ((CFrameWnd*)m_pMainWnd)->GetActiveDocument();
  
  // Initialize a CCreateContext to point to the active document.
  // With this context, the new view is added to the document
  // when the view is created in CView::OnCreate().
  CCreateContext newContext;
  newContext.m_pNewViewClass = NULL;
  newContext.m_pNewDocTemplate = NULL;
  newContext.m_pLastView = NULL;
  newContext.m_pCurrentFrame = NULL;
  newContext.m_pCurrentDoc = pCurrentDoc;
  
  // The ID of the initial active view is AFX_IDW_PANE_FIRST.
  // Incrementing this value by one for additional views works
  // in the standard document/view case but the technique cannot
  // be extended for the CSplitterWnd case.
  UINT viewID = AFX_IDW_PANE_FIRST + 1;
  CRect rect(0, 0, 0, 0); // Gets resized later.
  
  // Create the new view. In this example, the view persists for
  // the life of the application. The application automatically
  // deletes the view when the application is closed.
  m_pNewView->Create(NULL, "AnyWindowName", WS_CHILD, rect, m_pMainWnd, viewID, &newContext);
  
  // When a document template creates a view, the WM_INITIALUPDATE
  // message is sent automatically. However, this code must
  // explicitly send the message, as follows.
  m_pNewView->SendMessage(WM_INITIALUPDATE, 0, 0);
  ...
  4.实现切换功能函数(Switching Function)
  在MYWINAPP.CPP文件中添加如下代码，并保存。
  CView* CMyWinApp::SwitchView( )
  {
     CView* pActiveView =  ((CFrameWnd*) m_pMainWnd)->GetActiveView();
  
     CView* pNewView= NULL;
     if(pActiveView == m_pOldView)
        pNewView= m_pNewView;
     else
        pNewView= m_pOldView;
  
     // Exchange view window IDs so RecalcLayout() works.
     #ifndef _WIN32
     UINT temp = ::GetWindowWord(pActiveView->m_hWnd, GWW_ID);
     ::SetWindowWord(pActiveView->m_hWnd, GWW_ID, ::GetWindowWord(pNewView->m_hWnd, GWW_ID));
     ::SetWindowWord(pNewView->m_hWnd, GWW_ID, temp);
     #else
     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);
     #endif
     pActiveView->ShowWindow(SW_HIDE);
     pNewView->ShowWindow(SW_SHOW);
     ((CFrameWnd*) m_pMainWnd)->SetActiveView(pNewView);
     ((CFrameWnd*) m_pMainWnd)->RecalcLayout();
     pNewView->Invalidate();
     return pActiveView;
  }
  5.调用SwitchView函数的实现
  调用SwitchView函数可以通过增加菜单项来是实现。
  void CMainFrame::OnForm1()
  {
  SwitchView();
  }