Window Procedure Superclassing - Win32 Programmer's Reference

Custom Search

Window Procedure Superclassing

Superclassing is a technique that allows an application to create a new window class with the basic functionality of the existing class, plus enhancements provided by the application. A superclass is based on an existing window class called the base class. Frequently, the base class is a system global window class such as an edit control, but it can be any window class.

A superclass has its own window procedure, called the superclass procedure. The superclass procedure can take three actions upon receiving a message: It can pass the message to the original window procedure, modify the message and pass it to the original window procedure, or process the message and not pass it to the original window procedure. If the superclass procedure processes a message, it can do so before, after, or both before and after it passes the message to the original window procedure.

Unlike a subclass procedure, a superclass procedure can process window creation messages (WM_NCCREATE, WM_CREATE, and so on), but it must also pass them to the original base-class window procedure so that the base-class window procedure can perform its initialization procedure.

To superclass a window class, an application first calls the GetClassInfo function to retrieve information about the base class. GetClassInfo fills a WNDCLASS structure with the values from the WNDCLASS structure of the base class. Next, the application copies its own instance handle into the hInstance member of the WNDCLASS structure and copies the name of the superclass into the lpszClassName member. If the base class has a menu, the application must provide a new menu with the same menu identifiers and copy the menu name into the lpszMenuName member. If the superclass procedure processes the WM_COMMAND message and does not pass it to the window procedure of the base class, the menu need not have corresponding identifiers. GetClassInfo does not return the lpszMenuName, lpszClassName, or hInstance member of the WNDCLASS structure.

An application must also set the lpfnWndProc member of the WNDCLASS structure. The GetClassInfo function fills this member with the address of the original window procedure for the class. The application must save this address, to pass messages to the original window procedure, and then copy the address of the superclass procedure into the lpfnWndProc member. The application can, if necessary, modify any other members of the WNDCLASS structure. After it fills the WNDCLASS structure, the application registers the superclass by passing the address of the structure to the RegisterClass function. The superclass can then be used to create windows.

Because superclassing registers a new window class, an application can add to both the extra class bytes and the extra window bytes. The superclass must not use the original extra bytes for the base class or the window for the same reasons that an instance subclass or a global subclass should not use them. Also, if the application adds extra bytes for its use to either the class or the window instance, it must reference the extra bytes relative to the number of extra bytes used by the original base class. Because the number of bytes used by the base class may vary from one version of the base class to the next, the starting offset for the superclass's own extra bytes may also vary from one version of the base class to the next.

Last news from Greatis Software

    Nostalgia .Net     .Net is powerful, but not all-powerful, so sometimes we need to use Win32 API for our .Net applications. It's simple enough with Platform Invoke if you have Win32 skill, but we do not always have time to dig the ancient documentation, declare the special types that are compatible with Win32, find the values of the Win32's constants and so on. Nostalgia .Net offers several simple-to-use classes, and components that will allow you to forget about the headache of Win32 and just use the power of Win32 in your application the same way as you use the native. Net classes. More »

Recommended software for developers

    Ultimate Pack     Component pack for Delphi and C++ Builder that contains runtime form designer, runtime object inspector, print suite and much more for the very special price. More »

    Form Designer .Net     Unique runtime form design solution that allows to edit any form in .Net WinForms application at runtime with full source codes for only 300 euro! More »

    Print Suite .Net     Print Suite .Net is a set of components for easy printing texts, images and grids from your WinForms applications. Full C# source codes are available More »

    Gradient Controls .Net     Gradient Controls .Net offers controls with gradient background feature. Labels, panels and so on... Full C# source codes are available More »

    Greatis iGrid     iGrid plots drawing grid right over your desktop, so you can use it everywhere, with any drawing application without any special plugins for different graphic editors. More »

All the contacts and projects

Dmitry Vasiliev (just.dmitry)

More Online Helps

Win32 Programmer's Reference
Win32 Multimedia Programmer's Reference
OLE Programmer's Reference
Microsoft Windows Pen API Programmer's Reference
Microsoft Windows Sockets 2 Reference
Microsoft Windows Telephony API (TAPI) Programmer's Reference
Unix Manual Pages

greatis just4fun network