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 APIENTRY 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;

}