一.创建一个接口
struct ISimpleMsgBox : public IUnknown
{
// IUnknown
STDMETHOD_(ULONG, AddRef)() PURE;
STDMETHOD_(ULONG, Release)() PURE;
STDMETHOD(QueryInterface)(REFIID riid, void** ppv) PURE;
// ISimpleMsgBox
STDMETHOD(DoSimpleMsgBox)(HWND hwndParent, BSTR bsMessageText) PURE;
};
替代方案:使用idl文件定义接口,其会生成相关头文件,但可读性很差
二.声明一个C++类实现该接口
class CSimpleMsgBoxImpl : public ISimpleMsgBox
{
public:
CSimpleMsgBoxImpl();
virtual ~CSimpleMsgBoxImpl();
// IUnknown
STDMETHOD_(ULONG, AddRef)();
STDMETHOD_(ULONG, Release)();
STDMETHOD(QueryInterface)(REFIID riid, void** ppv);
// ISimpleMsgBox
STDMETHOD(DoSimpleMsgBox)(HWND hwndParent, BSTR bsMessageText);
protected:
ULONG m_uRefCount;
};
实现部分,只关注QueryInterface 和DoSimpleMsgBox 部分.
STDMETHODIMP CSimpleMsgBoxImpl::QueryInterface ( REFIID riid, void** ppv )
{
HRESULT hrRet = S_OK;
TRACE(">>> SimpleMsgBoxSvr: In CSimpleMsgBoxImpl::QueryInterface()\n" );
// Check that ppv really points to a void*.
if ( IsBadWritePtr ( ppv, sizeof(void*) ))
return E_POINTER;
// Standard QI initialization - set *ppv to NULL.
*ppv = NULL;
// If the client is requesting an interface we support, set *ppv.
if ( InlineIsEqualGUID ( riid, IID_IUnknown ))
{
*ppv = (IUnknown*) this;
TRACE(">>> SimpleMsgBoxSvr: Client QIed for IUnknown\n" );
}
else if ( InlineIsEqualGUID ( riid, __uuidof(ISimpleMsgBox) ))
{
*ppv = (ISimpleMsgBox*) this;
TRACE(">>> SimpleMsgBoxSvr: Client QIed for ISimpleMsgBox\n" );
}
else
{
hrRet = E_NOINTERFACE;
TRACE(">>> SimpleMsgBoxSvr: Client QIed for unsupported interface\n" );
}
// If we're returning an interface pointer, AddRef() it.
if ( S_OK == hrRet )
{
((IUnknown*) *ppv)->AddRef();
}
return hrRet;
}
//////////////////////////////////////////////////////////////////////
// ISimpleMsgBox methods
STDMETHODIMP CSimpleMsgBoxImpl::DoSimpleMsgBox ( HWND hwndParent, BSTR bsMessageText )
{
_bstr_t bsMsg = bsMessageText;
LPCTSTR szMsg = (TCHAR*) bsMsg; // Use _bstr_t to convert the string to ANSI if necessary.
TRACE(">>> SimpleMsgBoxSvr: In CSimpleMsgBoxImpl::DoSimpleMsgBox()\n" );
MessageBox ( hwndParent, szMsg, _T("Simple Message Box"), MB_OK );
return S_OK;
}
三.为接口和类指定各自指定一个GUID
使用vc++扩展方法
struct __declspec(uuid("{7D51904D-1645-4a8c-BDE0-0F4A44FC38C4}")) ISimpleMsgBox;
class __declspec(uuid("{7D51904E-1645-4a8c-BDE0-0F4A44FC38C4}")) CSimpleMsgBoxImpl;
这样便可以使用__uuidof关键字了
__uuidof使用方法介绍
属于VC++扩展语法
class Demo
{
};
class __declspec(uuid("B372C9F6-1959-4650-960D-73F20CD479BA")) Demo;
int main( void )
{
CLSID clsid = __uuidof(Demo);
}
http://baike.baidu.com/view/3883826.htm
四.创建类厂(必须创建)
每个类必须配有一个类厂,关注CreateInstance 和LockServer 方法.
CoCreateInstance方法内部会生命周期依赖这个接口
//////////////////////////////////////////////////////////////////////
// IClassFactory methods
STDMETHODIMP CSimpleMsgBoxClassFactory::CreateInstance ( IUnknown* pUnkOuter,
REFIID riid,
void** ppv )
{
HRESULT hrRet;
CSimpleMsgBoxImpl* pMsgbox;
TRACE(">>> SimpleMsgBoxSvr: In CSimpleMsgBoxClassFactory::CreateInstance()\n" );
// We don't support aggregation, so pUnkOuter must be NULL.
if ( NULL != pUnkOuter )
return CLASS_E_NOAGGREGATION;
// Check that ppv really points to a void*.
if ( IsBadWritePtr ( ppv, sizeof(void*) ))
return E_POINTER;
*ppv = NULL;
// Create a new COM object!
pMsgbox = new CSimpleMsgBoxImpl;
if ( NULL == pMsgbox )
return E_OUTOFMEMORY;
// QI the object for the interface the client is requesting.
hrRet = pMsgbox->QueryInterface ( riid, ppv );
// If the QI failed, delete the COM object since the client isn't able
// to use it (the client doesn't have any interface pointers on the object).
if ( FAILED(hrRet) )
delete pMsgbox;
return hrRet;
}
STDMETHODIMP CSimpleMsgBoxClassFactory::LockServer ( BOOL fLock )
{
// Increase/decrease the DLL ref count, according to the fLock param.
fLock ? g_uDllLockCount++ : g_uDllLockCount--;
TRACE(">>> SimpleMsgBoxSvr: In CSimpleMsgBoxClassFactory::LockServer(), new DLL ref count = %d\n", g_uDllLockCount );
return S_OK;
}
五.注册COM组件(手动注册）
万事俱备,现在要将其信息写入注册表,
1.实现DllRegisterServer和DllUnregisterServer方法,并将方法声明为STDAPI,表明属于导出函数
// DllRegisterServer() creates the registy entries that tells COM where our
// server is located and its threading model.
STDAPI DllRegisterServer()
{
HKEY hCLSIDKey = NULL, hInProcSvrKey = NULL;
LONG lRet;
TCHAR szModulePath [MAX_PATH];
TCHAR szClassDescription[] = _T("SimpleMsgBox class");
TCHAR szThreadingModel[] = _T("Apartment");
__try
{
// Create a key under CLSID for our COM server.
lRet = RegCreateKeyEx ( HKEY_CLASSES_ROOT, _T("CLSID\\{7D51904E-1645-4a8c-BDE0-0F4A44FC38C4}"),
0, NULL, REG_OPTION_NON_VOLATILE, KEY_SET_VALUE | KEY_CREATE_SUB_KEY,
NULL, &hCLSIDKey, NULL );
if ( ERROR_SUCCESS != lRet )
return HRESULT_FROM_WIN32(lRet);
// The default value of the key is a human-readable description of the coclass.
lRet = RegSetValueEx ( hCLSIDKey, NULL, 0, REG_SZ, (const BYTE*) szClassDescription,
sizeof(szClassDescription) );
if ( ERROR_SUCCESS != lRet )
return HRESULT_FROM_WIN32(lRet);
// Create the InProcServer32 key, which holds info about our coclass.
lRet = RegCreateKeyEx ( hCLSIDKey, _T("InProcServer32"), 0, NULL, REG_OPTION_NON_VOLATILE,
KEY_SET_VALUE, NULL, &hInProcSvrKey, NULL );
if ( ERROR_SUCCESS != lRet )
return HRESULT_FROM_WIN32(lRet);
// The default value of the InProcServer32 key holds the full path to our DLL.
GetModuleFileName ( g_hinstThisDll, szModulePath, MAX_PATH );
lRet = RegSetValueEx ( hInProcSvrKey, NULL, 0, REG_SZ, (const BYTE*) szModulePath,
sizeof(TCHAR) * (lstrlen(szModulePath)+1) );
if ( ERROR_SUCCESS != lRet )
return HRESULT_FROM_WIN32(lRet);
// The ThreadingModel value tells COM how it should handle threads in our DLL.
// The concept of apartments is beyond the scope of this article, but for
// simple, single-threaded DLLs, use Apartment.
lRet = RegSetValueEx ( hInProcSvrKey, _T("ThreadingModel"), 0, REG_SZ,
(const BYTE*) szThreadingModel,
sizeof(szThreadingModel) );
if ( ERROR_SUCCESS != lRet )
return HRESULT_FROM_WIN32(lRet);
}
__finally
{
if ( NULL != hCLSIDKey )
RegCloseKey ( hCLSIDKey );
if ( NULL != hInProcSvrKey )
RegCloseKey ( hInProcSvrKey );
}
return S_OK;
}
// DllUnregisterServer() deleted the registy entries that DllRegisterServer() created.
STDAPI DllUnregisterServer()
{
// Delete our registry entries. Note that you must delete from the deepest
// key and work upwards, because on NT/2K, RegDeleteKey() doesn't delete
// keys that have subkeys on NT/2K.
RegDeleteKey ( HKEY_CLASSES_ROOT, _T("CLSID\\{7D51904E-1645-4a8c-BDE0-0F4A44FC38C4}\\InProcServer32") );
RegDeleteKey ( HKEY_CLASSES_ROOT, _T("CLSID\\{7D51904E-1645-4a8c-BDE0-0F4A44FC38C4}") );
return S_OK;
}
2.定义def文件
EXPORTS
DllRegisterServer PRIVATE
DllUnregisterServer PRIVATE
DllGetClassObject PRIVATE
DllCanUnloadNow PRIVATE
3.编译通过后使用regsvr32命令,注册此dll组件
在调用此com组件之前,必须通过cmd命令注册,很重要,DllRegisterServer将会成为入口点,
六.编写DllGetClassObject
只有通过全局函数DllGetClassObject,才可以创建类厂,这个方法com类库会去调用,其会根据CLSID返回一个类工厂(一个dll可能会有多个com类)
生命周期(非常重要)：
CoCreateInstance->CoGetClassObject->DllGetClassObject->IClassFactory->CreateInstance
当理解上面流程后再看com技术内幕第七章很很有感觉
// DllGetClassObject() is called when COM needs to get a class factory.
STDAPI DllGetClassObject ( REFCLSID rclsid, REFIID riid, void** ppv )
{
HRESULT hrRet;
CSimpleMsgBoxClassFactory* pFactory;
TRACE(">>> SimpleMsgBoxSvr: In DllGetClassObject()\n");
// Check that the client is asking for the CSimpleMsgBoxImpl factory.
if ( !InlineIsEqualGUID ( rclsid, __uuidof(CSimpleMsgBoxImpl) ))
return CLASS_E_CLASSNOTAVAILABLE;
// Check that ppv really points to a void*.
if ( IsBadWritePtr ( ppv, sizeof(void*) ))
return E_POINTER;
*ppv = NULL;
// Construct a new class factory object.
pFactory = new CSimpleMsgBoxClassFactory;
if ( NULL == pFactory )
return E_OUTOFMEMORY;
// AddRef() the factory since we're using it.
pFactory->AddRef();
// QI() the factory for the interface the client wants.
hrRet = pFactory->QueryInterface ( riid, ppv );
// We're done with the factory, so Release() it.
pFactory->Release();
return hrRet;
}
七.调用com组件
void DoMsgBoxTest(HWND hMainWnd)
{
ISimpleMsgBox* pIMsgBox;
HRESULT hr;
hr = CoCreateInstance ( __uuidof(CSimpleMsgBoxImpl), NULL, CLSCTX_INPROC_SERVER,
__uuidof(ISimpleMsgBox), (void**) &pIMsgBox );
if ( FAILED(hr) )
return;
pIMsgBox->DoSimpleMsgBox ( hMainWnd, _bstr_t("Hello COM!") );
pIMsgBox->Release();
}
以上步骤不可以省略,可以看到创建一个com组件是比较麻烦的一个流程,很容易出错
或者先常见一个类工厂
HRESULT hr;
IClassFactory *pc=NULL;
hr=::CoGetClassObject(__uuidof(CSimpleMsgBoxImpl), CLSCTX_INPROC_SERVER,NULL,
IID_IClassFactory, (void**) &pc );
例子参考：