如何在一个FormView里获得另一个FormView的指针

 我的目标是:                     想从FormView A 向FormView B 发送自定义消息。
我的程序的窗口结构是:  有一个视图类CMyView, 和两个FormView：A和B
我遇到的问题是:              在FormView A里调用CMyDoc遍历视图类以找到FormView B取
                                           得的文档类指针却为0x00000000
我是这样做的：               1.在CMyDoc中创建GetView函数，内容如下：
                                              CView* CMyDoc::GetView()
                                              {
                                                    CView *pView ;
                                                    POSITION pos=GetFirstViewPosition();
                                                    while(pos!=NULL)
                                                    {
                                                         pView = GetNextView(pos);
                                                         if(pView->IsKindOf(RUNTIME_CLASS CFormViewB)))
                                                              break;
                                                    }
                                                    return pView;
                                              }
                                         2. 在FormViewA的按钮响应函数中，写了如下代码：
                                              void CFormViewA::OnButtonTest()
                                              {
                                                   CMainFrame *Frm = (CMainFrame*)AfxGetMainWnd();
                                                   CMyDoc* pDoc=(CMyDoc*)Frm->GetActiveDocument();
                                                   CView *pView=pDoc->GetView();
                                                   pView->PostMessage(WM_USRMSG,0,0);
                                               }

问题出在：                   语句CMyDoc* pDoc=(CMyDoc*)Frm->GetActiveDocument();调
                                       试到这里，查看pDoc的值为0x00000000，请问这是什么问题，
                                       该怎么解决

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解决方法：             1.（modaoshi3002）定义两个全局的视图变量 pA,pB，在各自的构造函数里写好：

                                  pA = this;pB= this;在要用到的文件里extern一下，搞定！

                                 2.我又找到了个办法,因为我的formViewB是由MainFrm的OnCreateClient分割而成的，于是： 
                                    CMainFrame*  pFrame  =  (CMainFrame*)AfxGetMainWnd(); 
                                    CFormViewB  *pView  =  (CFormViewB*)pFrame-  >m_wndSplitter.GetPane(1,0); 
                                    pView-  >PostMessage(WM_USRMSG,0,0); 

                                 3.题目中我的那个办法为什么不行，为啥不能获得文档指针呢？还没有解决。