QueryInterface 实现及使用的完整的例子

大家好，又见面了，我是你们的朋友全栈君。

下面我们将把前面所提到过和各代码段组合起来，以构成一个说明QueryInterface 实现及使用的完整例子。 总的来说可以将这些代码分成三部分。 第一部分是接口IX、 IY 和 IZ 的定义部分。接口 IUnknown 的定义在 Win32 SDK 的头文件 1 见UNKNWN . H 中。 第二部分是组件的实现。类 CA 实现了一个支持 IX 和 IY 接口的组件。QueryInterface的实现同前一节中给出的实现是一样的。在类CA的末尾给出了CreateInstance 的定义。客户可以使用此函数来创建类 CA 所代表的组件并返回一个指向其 IUnknown 接口的指针。 在定义好 CreateInstance函数之后，下面定义的是各接口的 IID 结构。从这些定义可以看出 IID 结构是一个相当大的结构。

清单中的第三部分也就是最后一部分是main 函数，它表示示例程序中的客户。

#include < iostream > #include < objbase.h > #include < windows.h > using namespace std;

void trace( const char * msg){cout << msg << endl;}

// interfaces interface IX:IUnknown { virtual void _stdcall Fx() = 0 ; };

interface IY:IUnknown { virtual void _stdcall Fy() = 0 ; };

interface IZ:IUnknown { virtual void _stdcall Fz() = 0 ; };

// forward references for guids extern const IID IID_IX; extern const IID IID_IY; extern const IID IID_IZ;

// component class CA: public IX, public IY { // IUnknown implementation virtual HRESULT _stdcall QueryInterface( const IID & iid, void ** ppv); virtual ULONG _stdcall AddRef(){ return 0 ;} virtual ULONG _stdcall Release(){ return 0 ;}

// interface IX implementation virtual void _stdcall Fx() {cout << “ FX “ << endl;MessageBox(NULL, “ hello world “ , “ caption “ ,MB_OK);}; // interface IY implementation virtual void _stdcall Fy(){cout << “ FY “ << endl;}

};

HRESULT _stdcall CA::QueryInterface( const IID & iid, void ** ppv) { if (iid == IID_IUnknown) { trace( “ QueryInterface:return pointer to IUnknown “ ); * ppv = static_cast < IX *> ( this ); }

else if (iid == IID_IX) { trace( “ QueryInterface:Return pointer to IX. “ ); * ppv = static_cast < IX *> ( this ); }

else if (iid == IID_IY) { trace( “ QuertyInterface:Return pointer to IY “ ); * ppv = static_cast < IY *> ( this ); } else { trace( “ QuertyInterface:Interface not supported “ ); * ppv = NULL; return E_NOINTERFACE; } reinterpret_cast < IUnknown *> ( * ppv) -> AddRef(); return S_OK;

}

// creation function IUnknown * CreateInstance() { IUnknown * pI = static_cast < IX *> ( new CA); pI -> AddRef(); return pI; }

// IIDS // {C225EDDE-ACFE-4349-AD2B-C7068731F8B3} static const IID IID_IX = { 0xc225edde , 0xacfe , 0x4349 , { 0xad , 0x2b , 0xc7 , 0x6 , 0x87 , 0x31 , 0xf8 , 0xb3 } };

// {6E3A34D9-1E23-433b-A393-1A4A6A965C80} static const IID IID_IY = { 0x6e3a34d9 , 0x1e23 , 0x433b , { 0xa3 , 0x93 , 0x1a , 0x4a , 0x6a , 0x96 , 0x5c , 0x80 } };

// {D8CDFA09-D552-41b9-AA44-8A70D8554A5C} static const IID IID_IZ = { 0xd8cdfa09 , 0xd552 , 0x41b9 , { 0xaa , 0x44 , 0x8a , 0x70 , 0xd8 , 0x55 , 0x4a , 0x5c } };

// client int main() { HRESULT hr; trace( “ client: Get an IUnknown pointer “ );

IUnknown * pIUnKnown = CreateInstance(); trace( “ client: Get interface IX “ );

IX * pIX = NULL; hr = pIUnKnown -> QueryInterface(IID_IX,( void ** ) & pIX); if (SUCCEEDED(hr)) { trace( “ client:Succeeded getting IX “ ); pIX -> Fx(); // use interface IX } trace( “ client: Get interface IY “ );

IY * pIY = NULL; hr = pIUnKnown -> QueryInterface(IID_IY,( void ** ) & pIY);

if (SUCCEEDED(hr)) { trace( “ client: Succeeded get IY “ ); pIY -> Fy(); // use interface IY }

trace( “ client:ask for an unsupporte interface “ );

IZ * pIZ = NULL;

hr = pIUnKnown -> QueryInterface(IID_IZ,( void ** ) & pIZ); if (SUCCEEDED(hr)) { trace( “ client:succeeded in geting interface iz “ ); pIZ -> Fz(); } else { trace( “ client: could not get interface IZ “ ); } trace( “ client: get interface IY from interface IX “ );

IY * pIYfromIX = NULL; hr = pIX -> QueryInterface(IID_IY,( void ** ) & pIYfromIX);

if (SUCCEEDED(hr)) { trace( “ client:succeeded getting IY “ ); pIYfromIX -> Fy(); } trace( “ client: get interface IUNkown from IY “ );

IUnknown * pIUnknownFromIY = NULL; hr = pIY -> QueryInterface(IID_IUnknown,( void ** ) & pIUnknownFromIY);

if (SUCCEEDED(hr)) { cout << “ Are the IUnknown pointers equal “ ; if (pIUnknownFromIY == pIUnKnown) { cout << “ Yes,pIUnknownFromIY==pIUnknown “ << endl; } else { cout << “ No,pIUnknownFrom IY!=pIUnknown “ << endl; } } // Delete the component delete pIUnKnown;

system( “ pause “ ); return 0 ;

}

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