CMDIChildWnd Class

Статья
10/16/2008

Provides the functionality of a Windows multiple document interface (MDI) child window, along with members for managing the window.

class CMDIChildWnd : public CFrameWnd

Заметки

An MDI child window looks much like a typical frame window, except that the MDI child window appears inside an MDI frame window rather than on the desktop. An MDI child window does not have a menu bar of its own, but instead shares the menu of the MDI frame window. The framework automatically changes the MDI frame menu to represent the currently active MDI child window.

To create a useful MDI child window for your application, derive a class from CMDIChildWnd. Add member variables to the derived class to store data specific to your application. Implement message-handler member functions and a message map in the derived class to specify what happens when messages are directed to the window.

There are three ways to construct an MDI child window:

Directly construct it using Create.
Directly construct it using LoadFrame.
Indirectly construct it through a document template.

Before you call Create or LoadFrame, you must construct the frame-window object on the heap using the C++ new operator. Before calling Create you can also register a window class with the AfxRegisterWndClass global function to set the icon and class styles for the frame.

Use the Create member function to pass the frame's creation parameters as immediate arguments.

LoadFrame requires fewer arguments than Create, and instead retrieves most of its default values from resources, including the frame's caption, icon, accelerator table, and menu. To be accessible by LoadFrame, all these resources must have the same resource ID (for example, IDR_MAINFRAME).

When a CMDIChildWnd object contains views and documents, they are created indirectly by the framework instead of directly by the programmer. The CDocTemplate object orchestrates the creation of the frame, the creation of the containing views, and the connection of the views to the appropriate document. The parameters of the CDocTemplate constructor specify the CRuntimeClass of the three classes involved (document, frame, and view). A CRuntimeClass object is used by the framework to dynamically create new frames when specified by the user (for example, by using the File New command or the MDI Window New command).

A frame-window class derived from CMDIChildWnd must be declared with DECLARE_DYNCREATE in order for the above RUNTIME_CLASS mechanism to work correctly.

The CMDIChildWnd class inherits much of its default implementation from CFrameWnd. For a detailed list of these features, please refer to the CFrameWnd class description. The CMDIChildWnd class has the following additional features:

In conjunction with the CMultiDocTemplate class, multiple CMDIChildWnd objects from the same document template share the same menu, saving Windows system resources.
The currently active MDI child window menu entirely replaces the MDI frame window's menu, and the caption of the currently active MDI child window is added to the MDI frame window's caption. For further examples of MDI child window functions that are implemented in conjunction with an MDI frame window, see the CMDIFrameWnd class description.

Do not use the C++ delete operator to destroy a frame window. Use CWnd::DestroyWindow instead. The CFrameWnd implementation of PostNcDestroy will delete the C++ object when the window is destroyed. When the user closes the frame window, the default OnClose handler will call DestroyWindow.

For more information on CMDIChildWnd, see Frame Windows.