Why is it necessary to RegisterClass in Windows API programming?

Question

I would like to ask why, in developing Windows GUI\'s using the API, is it necessary to register a window class? What is the concept of it?

I have already read the

Answer 1

Since you've tagged your question with C++ I'll give you a C++ analogy...

RegisterClass is basically you defining a class and including it in your program (much like a #include in C++). The WNDPROC is your handler for anything that happens within the window if and when an instance is created.

CreateWindow is conceptually the same as you doing a new in C++. You're asking Windows to create a new window, and you've got to tell it the type of window. Windows includes a set of predefined windows, such as Button or Edit, but if you want to create an instance of your own window then that's fine, you just need to tell it the "class" you'd like to create. You've already registered this class by calling RegisterClass, so Windows can now go straight to the definition and create an instance of your window.