实现类非静态成员函数做窗口过程函数

实现类非静态成员函数做窗口过程函数，无非是想办法把类对象指针传递给窗口过程。最简单的办法是使用全局变量，在很多场景下是快捷有效的办法。这里介绍的办法是借助::SetWindowLong(hWnd, GWL_USERDATA, (LONG)pWindow)调用，把类指针传递给窗口。在窗口过程函数中再调用 GetWindowLong来获取出来使用。

通过CreateWindowEx最后一个参数，把类指针传递给窗口，详见代码：

class CMyWindow
{
protected:
    static LRESULT CALLBACK WndProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
    {
        CMyWindow* pWindow;
        if (WM_NCCREATE == uMsg)
        {
            MDICREATESTRUCT* pMDIC = (MDICREATESTRUCT*)((LPCREATESTRUCT)lParam)->lpCreateParams;
            pWindow = (CMyWindow*)(pMDIC->lParam);
            ::SetWindowLong(hWnd, GWL_USERDATA, (LONG) pWindow);
        }
        else
        {
            pWindow=(CMyWindow*)::GetWindowLong(hWnd, GWL_USERDATA);
        }
        if (NULL != pWindow)
        {
            return pWindow->WndProc(hWnd, uMsg, wParam, lParam);
        }
        else
        {
            return ::DefWindowProc(hWnd, uMsg, wParam, lParam);
        }
    }
    virtual LRESULT WndProcSelf(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
    {
        //this is self wndproc
        return 0L;
    }
    virtual HWND CreateEx(DWORD dwExStyle,
        LPCTSTR lpszClass,
        LPCTSTR lpszName,
        DWORD dwStyle,
        int x, int y, 
        int nWidth, int nHeight, 
        HWND hParent, 
        HMENU hMenu, 
        HINSTANCE hInst)
    {
        MDICREATESTRUCT mdic;
        memset(& mdic, 0, sizeof(mdic));
        mdic.lParam = (LPARAM) this;
        return CreateWindowEx(dwExStyle,
            lpszClass,
            lpszName,
            dwStyle,
            x, y,
            nWidth, nHeight,
            hParent,
            hMenu,
            hInst,
            & mdic);
    }
private:
    HWND m_hWnd;
};