改变window的WndProc

Question

I try to change standart WndProc function. I have this code:

HWND btn = CreateWindowEx(WS_EX_TRANSPARENT | WS_EX_CLIENTEDGE, L"BUTTON", L"Window title", WS_TABSTOP | WS_VISIBLE | WS_CHILD | BS_DEFPUSHBUTTON
    , 50, 50, 50, 50, (HWND)XApplicationMainWindow->window->_wnd, (HMENU)123,
    (HINSTANCE)GetWindowLongPtr(XApplicationMainWindow->window->_wnd, GWLP_HINSTANCE), NULL);

SetWindowLongPtrW(btn, GWLP_WNDPROC, (LONG_PTR)SubclassWindowProc);

I can use L"BUTTON" class name, but when I change WndProc function I'll have a problem.

On this picture, you can see the blank square and normal button. If I try to create new WNDCLASS or WNDCLASSEX , I'll have nothing... Why?

How can I change the standart WndProc function, if I use L"BUTTON" class name?

It's my second WndProc :

LRESULT CALLBACK SubclassWindowProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam) {
    switch (uMsg) {
    case WM_CREATE:
        break;
    case WM_COMMAND:

        //Event click
        switch (LOWORD(wParam))
        {
        case 123:
            OutputDebugStringA("Subclass click2");
            break;
        default:
            break;
        }

        break;
    default:
        return DefWindowProc(hWnd, uMsg, wParam, lParam);
    }
    return 0;
}

Answer 1

DefWindowProc() is the wrong window procedure for your SubclassWindowProc() to be calling.

You need to call the previous window procedure that you are replacing - the window procedure that handles all of the button's default behaviors (like drawing the button so it actually looks like a button, and responding to user input like a button, etc). SetWindowLongPtr() returns a pointer to that procedure to you, but you are currently ignoring it.

See Subclassing Controls on MSDN for more details.

Try this instead:

WNDPROC btnWndProc;

LRESULT CALLBACK SubclassWindowProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam) {
    switch (uMsg) {
        case WM_COMMAND:
            //Event click
            switch (LOWORD(wParam))
            {
                case 123:
                    OutputDebugStringA("Subclass click2");
                    break;
            }

            break;
    }

    return CallWindowProc(hWnd, btnWndProc, uMsg, wParam, lParam);
}

...

HWND btn = CreateWindowEx(...);

btnWndProc = (WNDPROC) SetWindowLongPtrW(btn, GWLP_WNDPROC, (LONG_PTR)SubclassWindowProc);

Alternatively, using SetWindowSubclass() , which issafer than using SetWindowsLongPtr() , eg:

LRESULT CALLBACK SubclassWindowProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam, UINT_PTR uIdSubclass, DWORD_PTR dwRefData) {
    switch (uMsg) {
        case WM_NCDESTROY:
            RemoveWindowSubclass(hWnd, SubclassWindowProc, uIdSubclass);
            break;

        case WM_COMMAND:
            //Event click
            switch (LOWORD(wParam))
            {
                case 123:
                    OutputDebugStringA("Subclass click2");
                    break;
            }

            break;
    }

    return DefSubclassProc(hWnd, uMsg, wParam, lParam);
}

...

HWND btn = CreateWindowEx(...);

SetWindowSubclass(btn, SubclassWindowProc, 1, 0);

Now, that being said, your subclass will never call OutputDebugStringA() , because it will never receive the WM_COMMAND message you are expecting. When a button is clicked, a WM_COMMAND message is not sent to the button itself. The button posts a WM_COMMAND message to the button's parent window instead (in this case, to XApplicationMainWindow->window->_wnd ). So, you need to handle the WM_COMMAND message in the window procedure of the parent window , not in the window procedure of the button itself.

Otherwise, if you still want to subclass the button itself, you will have to handle the WM_LBUTTON(DOWN|UP) and WM_KEY(DOWN|UP) / WM_CHAR messages that the button receives and then subsequently translates into a WM_COMMAND message for its parent window.