c++ - 我怎样才能让 WinProc 访问由它创建的对象？

Question

在某些时候，我有这个

LRESULT CALLBACK WinProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    if(msg==WM_CREATE)
    {
        LPCREATESTRUCT pcs = (LPCREATESTRUCT)lParam;
            D2DResources* pD2DResources = (D2DResources*)pcs->lpCreateParams;

            ::SetWindowLongPtrW(
                hWnd,
                GWLP_USERDATA,
                PtrToUlong(pD2DResources)
                );
    }
    else
    {
        D2DResources* pD2DResources = reinterpret_cast<D2DResources*>(static_cast<LONG_PTR>(
            ::GetWindowLongPtrW(
                hWnd,
                GWLP_USERDATA
                )));

        switch(msg)
        {

    case WM_PAINT:
        {
            pD2DResources->OnRender();
            ValidateRect(hWnd, NULL);
        }
        break;

    case WM_SIZE:
        {
            UINT width = LOWORD(lParam);
            UINT height = HIWORD(lParam);
            pD2DResources->OnResize(width, height);
        }
        break;

所以我的 WinProc 可以访问以前创建的 D2DResources。现在我希望它能够访问另一个先前创建的对象。我怎么做？我的意思是，它可以访问多个先前创建的对象吗？如果是，怎么办？

编辑:Raymond Chen 说:“将指针作为 lpCreateParams 传递给结构。您可以在结构中放入任何您想要的东西。”我怎么做？谁能给我一个例子？

Answer 1

创建自己的结构，创建的时候传给窗口。你可以把任何你喜欢的东西放在那里，包括指向其他​​东西的指针。

例如

struct MyWindowData
{
    D2DResources*   pD2DResources;
    void*       pMyOtherData;
    int     iSomethingElse;
};


// on window creation
MyWindowData* pData = new MyWindowData(...);
HWND hWnd = CreateWindowEx(..., pData); // window will own the data and destroy it itself

// in the window procedure
if (msg == WM_CREATE)
{
    MyWindowData* pData = ((LPCREATESTRUCT)lParam)->lpCreateParams;
    SetWindowLongPtr(hWnd, GWLP_USERDATA, (ULONG_PTR)pData);
}
else
{
    MyWindowData* pData = (MyWindowData*)GetWindowLongPtr(hWnd, GWLP_USERDATA);
    switch (msg)
    {
        case WM_PAINT:
            pData->pD2DResources->OnRender();
            break;

        case WM_NCDESTROY:
            delete pData; // delete data on destroy
            break;
    }

    ...
}