Advanced MFC Programming

Chapter 13. Adding Special Features to Application
Member style specifies window styles, by setting different bits of this member we can create different
types of windows. There are many styles that can be combined together, two most often used styles are
CS_HREDRAW and CS_VREDRAW, which will cause the client area to be updated if user resizes the window in
either horizontal or vertical direction. Member lpfnWndProc points to a callback function that will be used
to process incoming messages. When a window is created, it should contain several default objects: 1) icon,
which will be used to draw the application when it is minimized; 2) cursor, which will be used to customize
the mouse cursor when it is located within the client window of the application; 3) default mainframe
menu; 4) brush, which will be used to erase the client area (This brush specifies the background pattern of
the window). The above objects are described by following members of structure WNDCLASS respectively:
hIcon, hCursor, hbrBackground and lpszMenuName.
Another very important member is lpszClassName, which describes the type of the window we will
create. Every window under Windows has a class name. Before creating a new type of window, we must
register its class name to the system. After that we can use this class name to implement an instance of
window. A class name is simply a string, which can be specified by the programmer.
If we write windows program in C, we must go through the following procedure in order to create a
new window: register the window class name, implement a message handling routine, use the registered
window class name to implement a new window instance. In MFC, this procedure is hidden behind the
classes, when we use a class derived from CWnd to declare a variable, the class registration is completed
sometime before the window is created. Also, we do not need to provide message handling routines
because there exist default message handlers in MFC. If we want to trap certain messages, we can add
member functions and use message mapping macros to associate the messages with functions.
It is relatively easy to implement one-instance application by programming in C: before registering a
window class, we can first find out if there exists any instance implemented by the same type of window
class (This class has nothing to do with class in C++) in the system. If so, we simply exit and do not go on
to create a new window. If not, we will implement the new window.
However, in MFC, we do not see how window class is registered, so it is difficult to manipulate it.
Also, in MFC, all the window class names are predefined, so we actually can not modify them. In order to
create one-instance application, we need to discard the default registered window class name, and use our
own class name to create new instance. By doing so, we are able to check if there already exists an instance
of this window type before creating a new one.
Function CWnd::PreCreateWindow(…)
The styles of a window (including the class name) can be modified just before it is created. In MFC,
function CWnd::PreCreateWindow(…) can be overridden for this purpose.
The input parameter of CWnd::PreCreateWindow(…) is a CREATESTRUCT type variable, which is passed
to the function by reference:
virtual BOOL CWnd::PreCreateWindow(CREATESTRUCT& cs);
Structure CREATESTRUCT contains a variety of window styles:
typedef struct tagCREATESTRUCT {
LPVOID lpCreateParams;
HANDLE hInstance;
HMENU hMenu;
HWND hwndParent;
int cy;
int cx;
int y;
int x;
LONG style;
LPCSTR lpszName;
LPCSTR lpszClass;
DWORD dwExStyle;
} CREATESTRUCT;
We can specify a new menu and use it as the mainframe menu. We can set the initial size and position
of the window. We can also specify window name, and customize many other styles. Within the structure,
392