6.DirectX基础和令人生畏的COM

在学习DX一堆接口之前的知识补充，小的不能再小了。

一个COM对象实际上就是实现大量界面的C++类或者是一套C++类， 一个界面就是一套函数。

如图：一个COM对象，有IGRAPHICS、ISOUND和IINPUT三个界面。

每一个界面都有大量的函数可以调用，COM技术要求用户创建的所有的界面必须从一个指定的基本类界面IUnknown中导出，以具备功能：引用计数和查询接口。

interface   IUnknown  
{  
          virtual   HRESULT   _stdcall   QueryInterface(const IID   & iid,   (void**) ip)=0;  
          virtual   ULONG   _stdcall   AddRef(void)=0;  
          virtual   ULONG   _stdcall   Release(void)=0;  
}   

IUnknown是所有接口的基础,他负责两项工作:   
          IUnknown::QueryInterface负责得到该组件的其他接口的指针。
         IUnknown::AddRef/Release负责管理该组件的生存期,但有人使用该组件时,保证该组件不会被意外删除;再没人使用该组件时,保证该组件被自动删除。

例子：

1、定义IX、IY两个接口

// define the IX interface
interface IX: IUnknown
{

virtual void __stdcall fx(void)=0;

};

// define the IY interface
interface IY: IUnknown
{

virtual void __stdcall fy(void)=0;

};

2、定义COM对象

class CCOM_OBJECT : public IX,
                    public IY
{
public:

CCOM_OBJECT() : ref_count(0) {}
~CCOM_OBJECT() {}

private:

virtual HRESULT __stdcall QueryInterface(const IID &iid, void **iface);
virtual ULONG __stdcall AddRef();
virtual ULONG __stdcall Release();

virtual void __stdcall fx(void) {cout << "Function fx has been called." << endl; }
virtual void __stdcall fy(void) {cout << "Function fy has been called." << endl; }

int ref_count;

};

3、具体实现QueryInterface、AddRef和Release

HRESULT __stdcall CCOM_OBJECT::QueryInterface(const IID &iid, void **iface)
{// requesting the IUnknown base interface
if (iid==IID_IUnknown)
{
cout << "Requesting IUnknown interface" << endl;
*iface = (IX*)this;

} // end if

// maybe IX?
if (iid==IID_IX)
{
cout << "Requesting IX interface" << endl;
*iface = (IX*)this;

} // end if
else // maybe IY
if (iid==IID_IY)
{
cout << "Requesting IY interface" << endl;
*iface = (IY*)this;

} // end if
else
{ // cant find it!
cout << "Requesting unknown interaface!" << endl;
*iface = NULL;
return(E_NOINTERFACE);
} // end else

// if everything went well cast pointer to IUnknown and call addref()
((IUnknown *)(*iface))->AddRef();

return(S_OK);

} // end QueryInterface

////////////////////////////////////////////////////////////////////////////////////////////////

ULONG __stdcall CCOM_OBJECT::AddRef()
{
// increments reference count
cout << "Adding a reference" << endl;
return(++ref_count);

} // end AddRef

///////////////////////////////////////////////////////////////////////////////////////////////

ULONG __stdcall CCOM_OBJECT::Release()
{
// decrements reference count
cout << "Deleting a reference" << endl;
if (--ref_count==0)
{
delete this;
return(0);
} // end if
else
return(ref_count);

} // end Release

4、创建实例

IUnknown *CoCreateInstance(void)
{IUnknown *comm_obj = (IX *)new(CCOM_OBJECT);

cout << "Creating Comm object" << endl;
comm_obj->AddRef();

return(comm_obj);

}

5、Main调用

// create the main COM object
IUnknown *punknown = CoCreateInstance() ;

// create two NULL pointers the the IX and IY interfaces
IX *pix=NULL;
IY *piy=NULL;

// from the original COM object query for interface IX
punknown->QueryInterface(IID_IX, (void **)&pix);

// try some of the methods of IX
pix->fx();

// release the interface
pix->Release();

 

// now query for the IY interface
punknown->QueryInterface(IID_IY, (void **)&piy);

// try some of the methods
piy->fy();

// release the interface
piy->Release();

// release the COM object itself
punknown->Release();

 

附源码:

// DEMO5_1.CPP - A ultra minimal working COM example // NOTE: not fully COM compliant // INCLUDES ////////////////////////////////////////////////////////////////////////////////// #include <stdio.h> #include <malloc.h> #include <iostream.h> #include <objbase.h> // note: you must include this header it contains important constants // you must use in COM programs // GUIDS ///////////////////////////////////////////////////////////////////////////////////// // these were all generated with GUIDGEN.EXE // {B9B8ACE1-CE14-11d0-AE58-444553540000} const IID IID_IX = { 0xb9b8ace1, 0xce14, 0x11d0, { 0xae, 0x58, 0x44, 0x45, 0x53, 0x54, 0x0, 0x0 } }; // {B9B8ACE2-CE14-11d0-AE58-444553540000} const IID IID_IY = { 0xb9b8ace2, 0xce14, 0x11d0, { 0xae, 0x58, 0x44, 0x45, 0x53, 0x54, 0x0, 0x0 } }; // {B9B8ACE3-CE14-11d0-AE58-444553540000} const IID IID_IZ = { 0xb9b8ace3, 0xce14, 0x11d0, { 0xae, 0x58, 0x44, 0x45, 0x53, 0x54, 0x0, 0x0 } }; // INTERFACES //////////////////////////////////////////////////////////////////////////////// // define the IX interface interface IX: IUnknown { virtual void __stdcall fx(void)=0; }; // define the IY interface interface IY: IUnknown { virtual void __stdcall fy(void)=0; }; // CLASSES AND COMPONENTS /////////////////////////////////////////////////////////////////// // define the COM object class CCOM_OBJECT : public IX, public IY { public: CCOM_OBJECT() : ref_count(0) {} ~CCOM_OBJECT() {} private: virtual HRESULT __stdcall QueryInterface(const IID &iid, void **iface); virtual ULONG __stdcall AddRef(); virtual ULONG __stdcall Release(); virtual void __stdcall fx(void) {cout << "Function fx has been called." << endl; } virtual void __stdcall fy(void) {cout << "Function fy has been called." << endl; } int ref_count; }; // CLASS METHODS //////////////////////////////////////////////////////////////////////////// HRESULT __stdcall CCOM_OBJECT::QueryInterface(const IID &iid, void **iface) { // this function basically casts the this pointer or the Iunknown // pointer into the interface requested, notice the comparison with // the GUIDs generated and defined in the begining of the program // requesting the IUnknown base interface if (iid==IID_IUnknown) { cout << "Requesting IUnknown interface" << endl; *iface = (IX*)this; } // end if // maybe IX? if (iid==IID_IX) { cout << "Requesting IX interface" << endl; *iface = (IX*)this; } // end if else // maybe IY if (iid==IID_IY) { cout << "Requesting IY interface" << endl; *iface = (IY*)this; } // end if else { // cant find it! cout << "Requesting unknown interaface!" << endl; *iface = NULL; return(E_NOINTERFACE); } // end else // if everything went well cast pointer to IUnknown and call addref() ((IUnknown *)(*iface))->AddRef(); return(S_OK); } // end QueryInterface //////////////////////////////////////////////////////////////////////////////////////////////// ULONG __stdcall CCOM_OBJECT::AddRef() { // increments reference count cout << "Adding a reference" << endl; return(++ref_count); } // end AddRef /////////////////////////////////////////////////////////////////////////////////////////////// ULONG __stdcall CCOM_OBJECT::Release() { // decrements reference count cout << "Deleting a reference" << endl; if (--ref_count==0) { delete this; return(0); } // end if else return(ref_count); } // end Release /////////////////////////////////////////////////////////////////////////////////////////////// IUnknown *CoCreateInstance(void) { // this is a very basic implementation of CoCreateInstance() // it creates an instance of the COM object, in this case // I decided to start with a pointer to IX -- IY would have // done just as well IUnknown *comm_obj = (IX *)new(CCOM_OBJECT); cout << "Creating Comm object" << endl; // update reference count comm_obj->AddRef(); return(comm_obj); } // end CoCreateInstance /////////////////////////////////////////////////////////////////////////////////////////////// void main(void) { // create the main COM object IUnknown *punknown = CoCreateInstance(); // create two NULL pointers the the IX and IY interfaces IX *pix=NULL; IY *piy=NULL; // from the original COM object query for interface IX punknown->QueryInterface(IID_IX, (void **)&pix); // try some of the methods of IX pix->fx(); // release the interface pix->Release(); // now query for the IY interface punknown->QueryInterface(IID_IY, (void **)&piy); // try some of the methods piy->fy(); // release the interface piy->Release(); // release the COM object itself punknown->Release(); } // end main