Relationships Among MFC Objects
To help put the document/view creation process in perspective, consider a running program: a document, the frame window used to contain the view, and the view associated with the document.
A document keeps a list of the views of that document and a pointer to the document template that created the document.
A view keeps a pointer to its document and is a child of its parent frame window.
A document frame window keeps a pointer to its current active view.
A document template keeps a list of its open documents.
The application keeps a list of its document templates.
Windows keeps track of all open windows so it can send messages to them.
These relationships are established during document/view creation. The following table shows how objects in a running program can access other objects. Any object can obtain a pointer to the application object by calling the global function AfxGetApp.
Gaining Access to Other Objects in Your Application
From object |
How to access other objects |
|---|---|
Document |
Use GetFirstViewPosition and GetNextView to access the document's view list. Call GetDocTemplate to get the document template. |
View |
Call GetDocument to get the document. Call GetParentFrame to get the frame window. |
Document frame window |
Call GetActiveView to get the current view. Call GetActiveDocument to get the document attached to the current view. |
MDI frame window |
Call MDIGetActive to get the currently active CMDIChildWnd. |
Typically, a frame window has one view, but sometimes, as in splitter windows, the same frame window contains multiple views. The frame window keeps a pointer to the currently active view; the pointer is updated any time another view is activated.
注意
A pointer to the main frame window is stored in the m_pMainWnd member variable of the application object. A call to OnFileNew in your override of the InitInstance member function of CWinApp sets m_pMainWnd for you. If you do not call OnFileNew, you must set the variable's value in InitInstance yourself. (SDI COM component (server) applications may not set the variable if /Embedding is on the command line.) Note that m_pMainWnd is now a member of class CWinThread rather than CWinApp.