Registering Child and Frame Window Classes

A typical MDI application must register two window classes: one for its frame window and one for its child windows. If an application supports more than one type of document (for example, a spreadsheet and a chart), it must register a window class for each type.

The class structure for the frame window is similar to the class structure for the main window in non-MDI applications. The class structure for the MDI child windows differs slightly from the structure for child windows in non-MDI applications as follows:

• The class structure should have an icon, because the user can minimize an MDI child window as if it were a normal application window.
• The menu name should be NULL, because an MDI child window cannot have its own menu.
• The class structure should reserve extra space in the window structure. With this space, the application can associate data, such as a filename, with a particular child window.

The following example shows how Multipad registers its frame and child window classes.

BOOL WINAPI InitializeApplication() 
{ 
    WNDCLASS wc; 
 
    // Register the frame window class. 
 
    wc.style         = 0; 
    wc.lpfnWndProc   = (WNDPROC) MPFrameWndProc; 
    wc.cbClsExtra    = 0; 
    wc.cbWndExtra    = 0; 
    wc.hInstance     = hInst; 
    wc.hIcon         = LoadIcon(hInst, IDMULTIPAD); 
    wc.hCursor       = LoadCursor((HANDLE) NULL, IDC_ARROW); 
    wc.hbrBackground = (HBRUSH) (COLOR_APPWORKSPACE + 1); 
    wc.lpszMenuName  = IDMULTIPAD; 
    wc.lpszClassName = szFrame; 
 
    if (!RegisterClass (&wc) ) 
        return FALSE; 
 
    // Register the MDI child window class. 
 
    wc.lpfnWndProc   = (WNDPROC) MPMDIChildWndProc; 
    wc.hIcon         = LoadIcon(hInst, IDNOTE); 
    wc.lpszMenuName  = (LPCTSTR) NULL; 
    wc.cbWndExtra    = CBWNDEXTRA; 
    wc.lpszClassName = szChild; 
 
    if (!RegisterClass(&wc)) 
        return FALSE; 
 
    return TRUE; 
}