《COM原理与应用》学习笔记——一个简单的COM组件的实现

　　今天带来一个简单的COM组件的实现，非常的简单。这个组件只是简单的完成了整数的加减乘除~

首先，先罗列需要的COM接口，这里需要的接口非常简单，就是加减乘除的接口。所以定义一个ICalc类，当然这个类继承于IUnknown。

class ICalc : public IUnknown
{
public:
    virtual long __stdcall add(long a, long b) = 0;
    virtual long __stdcall minus(long a, long b) = 0;
    virtual long __stdcall times(long a, long b) = 0;
    virtual long __stdcall devide(long a, long b) = 0;
};

这只是定义了一个接口，接着我们要定义COM对象类，COM对象类理所当然的要继承自ICalc类。其中override是C++11提供的新关键字，表示明确的覆盖父类的某个函数。

class CCalc : public ICalc
{
public:
    CCalc();
    ~CCalc() = default;

public:
    //IUnknown interface:
    virtual HRESULT __stdcall QueryInterface(const IID &iid, void **ppv) override;
    virtual ULONG __stdcall AddRef() override;
    virtual ULONG __stdcall Release() override;

    //ICalc interface:
    virtual long __stdcall add(long a, long b) override;
    virtual long __stdcall minus(long a, long b) override;
    virtual long __stdcall times(long a, long b) override;
    virtual long __stdcall devide(long a, long b) override;

private:
    long m_lRef;//用于计数的变量
};

接着是类厂的定义，定义如下：

class CCalcFactory : public IClassFactory
{
public:
    CCalcFactory();
    ~CCalcFactory() = default;

public:
    //STDMETHODCALLTYPE = __stdcall
    //IUnknown interface:
    virtual HRESULT STDMETHODCALLTYPE QueryInterface(const IID &iid, void **ppv) override;
    virtual ULONG STDMETHODCALLTYPE AddRef() override;
    virtual ULONG STDMETHODCALLTYPE Release() override;

    //IClassFactory interface:
    virtual HRESULT STDMETHODCALLTYPE CreateInstance(IUnknown *pUnkOuter, const IID &iid, void **ppv) override;
    virtual HRESULT STDMETHODCALLTYPE LockServer(BOOL fLock) override;

protected:
    long m_lRef;
};

 接下来讲解以上各个类的具体实现：

首先是Ccalc的实现，那几个加减乘除的接口我就不写了。

HRESULT CCalc::QueryInterface(const IID &iid, void **ppv)
{
    if (iid == IID_Calc)
    {
        *ppv = (ICalc *) this;
        ((ICalc *)(*ppv))->AddRef();
    } 
    else if (iid == IID_IUnknown)
    {
        *ppv = (ICalc *) this;
        ((ICalc *)(*ppv))->AddRef();
    }
    else
    {
        *ppv = NULL;
        return E_NOINTERFACE;
    }

    return S_OK;
}

ULONG CCalc::AddRef()
{
    ++m_lRef;
    return (ULONG)m_lRef;
}

ULONG CCalc::Release()
{
    --m_lRef;
    //当引用计数变为0的时候就将COM对象删除，并将COM对象的引用减一以便COM库知道能否释放资源
    if (m_lRef == 0)
    {
        --g_ulCalcNumber;
        delete this;
        return 0;

    }
    return (ULONG)m_lRef;
}

接下来是类厂的实现：

extern ULONG g_ulCalcNumber;
extern ULONG g_ulLockNumber;

CCalcFactory::CCalcFactory()
{
    m_lRef = 0;
}

HRESULT CCalcFactory::QueryInterface(const IID &iid, void **ppv)
{ 
    if (iid == IID_IUnknown)
    {//返回自己的IUnknown指针
        *ppv = (IUnknown *)this;
        ((IUnknown *)(*ppv))->AddRef();
    }
    else if (iid == IID_IClassFactory)
    {//如果IID是类厂的IID就返回自己的接口指针以便客户程序能够用该指针创建COM对象
        *ppv = (IClassFactory *)this;
        ((IClassFactory *)(*ppv))->AddRef();
    }
    else
    {
        *ppv = NULL;
        return E_NOINTERFACE;
    }

    return S_OK;
}

ULONG CCalcFactory::AddRef()
{
    ++m_lRef;
    return (ULONG)m_lRef;
}

ULONG CCalcFactory::Release()
{
    --m_lRef;
    if (m_lRef == 0)
    {
        delete this;
        return 0;
    }
    return (ULONG)m_lRef;
}

HRESULT CCalcFactory::CreateInstance(IUnknown *pUnkOuter, const IID &iid, void **ppv)
{
    CCalc *pObj;
    HRESULT result;
    
    if (NULL != pUnkOuter)
    {
        return CLASS_E_NOAGGREGATION;
    }

    pObj = new (std::nothrow) CCalc;
    if (pObj == NULL)
    {
        return E_OUTOFMEMORY;
    }

    result = pObj->QueryInterface(iid, ppv);
    if (result != S_OK)
    {
        --g_ulCalcNumber;
        delete pObj;
    }

    return result;
}

HRESULT CCalcFactory::LockServer(BOOL fLock)
{
    if (fLock)
    {
        ++g_ulLockNumber;
    } 
    else
    {
        --g_ulLockNumber;
    }
    return NOERROR;
}

其他重要函数的实现：

//这个导出函数是COM库用来创建类厂对象的函数，函数原型必须这样写。
extern "C" HRESULT __stdcall DllGetClassObject(const CLSID &clsid, const IID &iid, LPVOID *ppv)
{
    if (clsid == CLSID_CCalc)
    {
        //创建类厂对象
        CCalcFactory *pCCalcFactory = new (std::nothrow)CCalcFactory;

        if (pCCalcFactory == NULL)
        {
            return E_OUTOFMEMORY;
        }
        else
        {
            //返回类厂对象的指针
            HRESULT result = pCCalcFactory->QueryInterface(iid, ppv);
            return result;
        }
    } 
    else
    {
        return CLASS_E_CLASSNOTAVAILABLE;
    }
}
    

//COM库用来查看是否可以卸载COM对象的函数
extern "C" HRESULT __stdcall DllCanUnloadNow()
{
    //当COM对象的引用计数为0，类厂没有被锁，那么就可以卸载
    if (g_ulCalcNumber == 0 && g_ulLockNumber == 0)
    {
        return S_OK;
    } 
    else
    {
        return S_FALSE;
    }
}

//注册函数，将COM插件注册到注册表中
extern "C" HRESULT __stdcall DllRegisterServer()
{
    char szModule[1024];
    DWORD dwResult = ::GetModuleFileName((HMODULE)g_hModule, (LPWSTR)szModule, 1024);
    if (dwResult == 0)
        return SELFREG_E_CLASS;
    return RegisterServer(CLSID_CCalc,
        szModule,
        "Calc.Object",
        "Calc Component",
        NULL);
}

//反注册函数，也可以说是注销函数吧。
extern "C" HRESULT __stdcall DllUnregisterServer()
{
    return UnregisterServer(CLSID_CCalc,
        "Calc.Object", NULL);
}

里面的具体注册过程什么的我也是拷贝的其他人的代码。具体请参见附件中的代码。

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