QueryInterface问题 | QueryInterface

本文介绍了QueryInterface问题的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

大家好，
我试图通过使用以下代码段来使用QueryInterface. com组件是由我创建的，它具有两个接口.但是"queryinterface"返回E_NOINTERFACE.
请Kindlly帮我解决这个问题.
谢谢，
Ganesamoorthy

Hi All,
I have tried to use QueryInterface by using the following code segment. the com component had been created by me and which has two interfaces. But the "queryinterface" returns E_NOINTERFACE.
Kindlly help me, to come out of this issue.
Thanks,
Ganesamoorthy

 HRESULT hr;
IGreet *greetObject;
IGreet2 *greetObject2;
CString strTemp;
hr = CoInitialize(NULL);
if (FAILED(hr) )
    return ;
hr = CoCreateInstance(CLSID_Greet2,NULL,CLSCTX_INPROC_SERVER, IID_IGreet2,(void **) & greetObject2);
if (FAILED(hr) )
{
    CoUninitialize();
    return ;
}
greetObject2->AddRef();
cout << greetObject->Sayhello("Ganesh") << endl;
CComBSTR bstrVal, bstrVal1;

bstrVal1.Append ("Ganesh");
greetObject2->SayHello2(bstrVal1, & bstrVal);
strTemp.Format (_T("%s"), bstrVal);
MessageBox (strTemp);
hr = greetObject2->QueryInterface(IID_IGreet,(void **)& greetObject);
DWORD dw = GetLastError();
if (FAILED(hr) )
{
    CoUninitialize();
    return ;
}
CoUninitialize();

推荐答案

HRESULT __stdcall Greet2::QueryInterface(REFIID riid, void **ppObj)
{
    if(riid == IID_IUnknown || riid == IID_IGreet2)
    {
        *ppObj = static_cast<IGreet2*>(this) ;
        reinterpret_cast<IUnknown*> (*ppObj)->AddRef();
        return S_OK;
    }
    else if(riid == IID_Greet)
    {
        *ppObj = static_cast<IGreet*>(this) ;
        reinterpret_cast<IUnknown*> (*ppObj)->AddRef();
        return S_OK;
    }
    else
    {
        *ppObj = NULL;
        return E_NOINTERFACE;
    }
}

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