Question

I have a problem with attaching a windows procedure to a window.

I have a baseclass called BaseWindow, that uses GWPL_USERDATA to call a virtual function called HandleMessage() of the child classes.

However, if i try to change the window procedure without creating a custom Window Class, it gives a type error from the child procedure to long.

Here’s the code:

static LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    BaseWindow *pThis = NULL;

    if (uMsg == WM_NCCREATE)
    {
        CREATESTRUCT* pCreate = (CREATESTRUCT*)lParam;
        pThis = (BaseWindow*)pCreate->lpCreateParams;
        SetWindowLongPtr(hwnd, GWLP_USERDATA, (LONG_PTR)pThis);

        pThis->m_hwnd = hwnd;
    }
    else
    {
        pThis = (BaseWindow*)GetWindowLongPtr(hwnd, GWLP_USERDATA);
    }
    if (pThis)
    {
        return pThis->HandleMessage(uMsg, wParam, lParam);
    }
    else
    {
        return DefWindowProc(hwnd, uMsg, wParam, lParam);
    }
}

virtual LRESULT HandleMessage(UINT uMsg, WPARAM wParam, LPARAM lParam)
    {return 0;};


PlayList Class : BaseWindow

SetWindowLong(m_hwnd, GWL_WNDPROC,(long)  HandleMessage); //Error

LRESULT PlayList::HandleMessage(UINT message,WPARAM wParam,LPARAM lParam) //Need to     attach this window procedure
{}

It works if the child procedure is static, however I use non static members in that procedure.

I want to subclass a common control, while using this base class (because a lot of code is redundant), is it possible?

Here’s the whole code for the base class: http://pastebin.com/ME8ks7XK

Answer 1

The compiler doesn’t like your declaration for HandleMessage, it isn’t static. It’s missing CALLBACK too, not good.

Not sure why you are trying to do this, the whole point of your WindowProc() function is to get the message forwarded to a virtual HandleMessage() method. At best you’d use WindowProc in your SetWindowLong() call instead of HandleMesssage. Or just specify it directly in the CreateWindowEx() call.