C++ Direct2D ID2D1HwndRenderTarget 的父 IUnknown 类的_vfptr变量变为 null

我有一个我正在制作的Direct2D应用程序，并且我正在编写一个Direct2D库，该库也使我更轻松地使用Direct2D。如果需要的话，我将发布确切的有问题的代码，但是我的主要问题是我在一个类的定义中有一个ID2D1HWNDRENDERDARGET，我将与另一个类扩展该类初始化渲染目标的父类，然后又调用子类的负载方法。但是，一旦该程序达到子类的负载内容方法，__vfptr变量（我不知道那是什么），在ID2D1HWNDRENDERDERTARGET的IUNKNOWN部分中，现在为无效。我觉得这一点的唯一原因是，在使用渲染目标从IwicbitMapsource创建ID2D1BITMAP时，我在其他一些代码中遇到了违规错误。我不明白这是怎么发生的，因为在初始化渲染目标后，_vfptr变量在初始化代码返回的方法后立即变为null。谁能解释为什么会发生这种情况？我的相关代码在下面。

此代码一次来创建HWND渲染目标和屏幕外渲染目标。这是在DLL项目中。gamebase.cpp

HRESULT GameBase::Initialize(HINSTANCE hInst, HWND winHandle, struct DX2DInitOptions options)
        {
            this->mainRenderTarget = NULL;
            this->offscreenRendTarget = NULL;
            this->factory = NULL;
            HRESULT result;
            D2D1_FACTORY_OPTIONS factOptions;
            D2D1_FACTORY_TYPE factType;
            if(options.enableDebugging)
                factOptions.debugLevel = D2D1_DEBUG_LEVEL::D2D1_DEBUG_LEVEL_ERROR;
            else
                factOptions.debugLevel = D2D1_DEBUG_LEVEL::D2D1_DEBUG_LEVEL_NONE;
            if(options.singleThreadedApp)
                factType = D2D1_FACTORY_TYPE_SINGLE_THREADED;
            else
                factType = D2D1_FACTORY_TYPE_MULTI_THREADED;
            result = D2D1CreateFactory(factType, factOptions, &this->factory);
            if(FAILED(result))
            {
                OutputDebugString(L"Failed to create a Direct 2D Factory!");
                return result;
            }
            this->instance = hInst;
            this->hwnd = winHandle;
            D2D1_SIZE_U size = D2D1::SizeU(options.winWidth, options.winHeight);
            this->width = options.winWidth;
            this->height = options.winHeight;
            result = factory->CreateHwndRenderTarget(D2D1::RenderTargetProperties(), D2D1::HwndRenderTargetProperties(winHandle, size), &this->mainRenderTarget);
            if(FAILED(result))
            {
                OutputDebugString(L"Failed to create a render target to draw to the window with!");
                return result;
            }
            result = this->mainRenderTarget->CreateCompatibleRenderTarget(&this->offscreenRendTarget);
            if(FAILED(result))
            {
                OutputDebugString(L"Failed to create an offscreen render target from the main render target.");
                return result;
            }
            return LoadContent();
        }

在致电LoadContent之后，我绝不会更改MainrenderTarget的值。

dx2dimage.cpp

HRESULT DX2DImageLoader::LoadFromResource(LPCWSTR resourceName, LPCWSTR resourceType, HMODULE progModule, DX2DImage* image)
        {
            if(!this->isInit)
            {
                OutputDebugStringA("You must call InitializeImageLoader before using this image loader!");
                return E_FAIL;
            }
            IWICBitmapDecoder *decoder = NULL;
            IWICBitmapFrameDecode *source = NULL;
            IWICStream *stream = NULL;
            IWICFormatConverter *converter = NULL;
            HRSRC imageResHandle = NULL;
            HGLOBAL imageResDataHandle = NULL;
            void *imageFile = NULL;
            DWORD imageFileSize = 0;
            HRESULT result;

            //Find the image.
            imageResHandle = FindResource(progModule, resourceName, resourceType);
            if(!imageResHandle)
            {
                OutputDebugStringA("Failed to get a handle to the resource!");
                return E_FAIL;
            }
            //Load the data handle of the image.
            imageResDataHandle = LoadResource(progModule, imageResHandle);
            if(!imageResDataHandle)
            {
                OutputDebugStringA("Failed to load the image from the module!");
                return E_FAIL;
            }
            //Lock and retrieve the image.
            imageFile = LockResource(imageResDataHandle);
            if(!imageFile)
            {
                OutputDebugStringA("Failed to lock the image in the module!");
                return E_FAIL;
            }
            //Get the size of the image.
            imageFileSize = SizeofResource(progModule, imageResHandle);
            if(!imageFileSize)
            {
                OutputDebugStringA("Failed to retrieve the size of the image in the module!");
                return E_FAIL;
            }
            //Create a stream that will read the image data.
            result = this->factory->CreateStream(&stream);
            if(FAILED(result))
            {
                OutputDebugStringA("Failed to create an IWICStream!");
                return result;
            }
            //Open a stream to the image.
            result = stream->InitializeFromMemory(reinterpret_cast<BYTE*>(imageFile), imageFileSize);
            if(FAILED(result))
            {
                OutputDebugStringA("Failed to initialize the stream!");
                return result;
            }
            //Create a decoder from the stream
            result = this->factory->CreateDecoderFromStream(stream, NULL, WICDecodeMetadataCacheOnDemand, &decoder);
            if(FAILED(result))
            {
                OutputDebugStringA("Failed to create a decoder from the stream!");
                return result;
            }
            //Get the first frame from the image.
            result = decoder->GetFrame(0, &source);
            if(FAILED(result))
            {
                OutputDebugStringA("Failed to get the first frame from the decoder!");
                return result;
            }
            //Create a format converter to convert image to 32bppPBGRA
            result = this->factory->CreateFormatConverter(&converter);
            if(FAILED(result))
            {
                OutputDebugStringA("Failed to create a format converter!");
                return result;
            }
            //Convert the image to the new format.
            result = converter->Initialize(source, GUID_WICPixelFormat32bppPBGRA, WICBitmapDitherTypeNone, NULL, 0.0f, WICBitmapPaletteTypeMedianCut);
            if(FAILED(result))
            {
                OutputDebugStringA("Failed to convert the image to the correct format!");
                return result;
            }
            //Create the Direct2D Bitmap from the Wic Bitmap.
            result = this->renderTarget->CreateBitmapFromWicBitmap(converter, NULL, &image->bitmap);
            if(FAILED(result))
            {
                OutputDebugStringA("Failed to create a Direct 2D Bitmap from a WIC Bitmap!");
                return result;
            }
            image->width = static_cast<UINT>(image->bitmap->GetSize().width);
            image->height = static_cast<UINT>(image->bitmap->GetSize().height);
            SafeRelease(&source);
            SafeRelease(&converter);
            SafeRelease(&decoder);
            SafeRelease(&stream);
            return S_OK;
        }

访问违规例外发生在线

result = this->renderTarget->CreateBitmapFromWicBitmap(converter, NULL, &image->bitmap);

其中image-> bitmap是当前的null（应该是应该是）ID2D1BITMAP。

在这里，RenderTarget变量是上面的gameBase.cpp的MainrenderTarget变量。当我调试线路时，所有rendertarget的父母都不是无效的，但是一旦我到达iunknown界面下方，_vfpptr的事情就无效了。转换器变量，此变量或图像变量并非如此。