Is there anything terrible would happen if I embed a message loop of a "child" window into the window procedure of a parent window?

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Is there anything terrible would happen if I embed a message loop of a "child" window into the window procedure of a parent window?

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Hi All,

I'm new to Win32 GUI programming and have a question described following.

Things goes like this: I have successfully created and showed a window, FirstWnd, with a menu bar.
There's a button in the menu bar which creates another window ( Let's call it CildWnd for now. I set the hWndParent parameter of CreateWindow to be the handle of FirstWnd when create CildWnd ) in the window procedure of FirstWnd. At the same place, the message loop of CildWnd is entered.

My code runs well. When CildWnd is created and showed, FirstWnd is still able to process message. But shouldn't it be blocked? After all, the message loop of CildWnd in its window procedure is still looping!

It's possible that my program is so simple that nothing goes wrong with such coding style.

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Answer 1

RLWA32 52,366

I think you are confusing message loops with window procedures. In a simple example like yours, messages for all of the windows that are created by a thread are dispatched by a single message loop. The dispatched messages are routed by Windows to the window procedure for the related window.

The parent and child windows have their own window procedures, and a single message loop dispatches messages to them.

Read more at messages-and-message-queues

Displame 21 Reputation points

2021-05-16T00:02:32.53+00:00

Thanks a lot. I got some ideas now.

I thought that message loop is window-specified, but it isn't the case.

The message loop embedded in the procedure of FirstWnd is not special to CildWnd. It is able to get and dispatch any message in the message queue of the current thread, so the message for FirstWnd will still be handled and routed to the correct window procedure.

Thank you!
RLWA32 52,366 Reputation points

2021-05-16T10:46:16.803+00:00

The message loop embedded in the procedure of FirstWnd...

I'm not sure what the above means. So I want to be clear that the message loop would not be embedded within any window procedure. For example, see the placement of the message loop in the Microsoft example code at Creating a Message Loop

Displame 21

My code is something like this:

Proc_of_CildWnd(message){
        /*Some code*/
    }
Proc_of_FirstWnd(message){
        switch(message){
            /*Other cases*`enter code here`/
            case creat_CildWnd:{
                /*Create and show CildWnd*/
                MSG mes;
                while(getmessage(mes)){
                    /*Translate and dispatch messages*/
                }
            }
        }
    }

WinMain(){
        /*Register FirstWnd and CildWnd*/
        /*Create and show FirstWnd*/
        MSG mes;
        while(getmessage(mes)){
            /*Translate and dispatch messages*/
        }
        /*...*/
    }

Now I know that such style is unnecessary and unwanted.

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Is there anything terrible would happen if I embed a message loop of a "child" window into the window procedure of a parent window?

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