详细解读COM中集合和枚举器笔记(2)枚举器内部实现

一.ATL枚举器接口

CComIEnum通用枚举器接口

template[span style="color: rgba(0, 0, 255, 1)">class T>

class ATL_NO_VTABLE CComIEnum :

public IUnknown

{

public:

STDMETHOD(Next)(

In ULONG celt,

Out T rgelt,

_Outopt ULONG pceltFetched) = 0;

STDMETHOD(Skip)(In ULONG celt) = 0;

STDMETHOD(Reset)(void) = 0;

STDMETHOD(Clone)(_Derefout CComIEnum ppEnum) = 0;

};

二.CComEnumImpl定义

template [span style="color: rgba(0, 0, 255, 1)">class Base, const IID piid, class T, class Copy>

class ATL_NO_VTABLE CComEnumImpl :

public Base

{

public:

CComEnumImpl()

{

m_begin = m_end = m_iter = NULL;

m_dwFlags = 0;

}

virtual ~CComEnumImpl();

STDMETHOD(Next)(

//代码效果参考：http://www.zidongmutanji.com/zsjx/367637.html

Out T rgelt,

_Outopt ULONG* pceltFetched);

STDMETHOD(Skip)(In ULONG celt);

STDMETHOD(Reset)(void)

{

m_iter = m_begin;

return S_OK;

}

STDMETHOD(Clone)(_Derefout Base ppEnum);

HRESULT Init(

In T begin,

In T end,

_Inopt IUnknown pUnk,

In CComEnumFlags flags = AtlFlagNoCopy);

CComPtr m_spUnk;

T m_begin;

T m_end;

T m_iter;

DWORD m_dwFlags;

protected:

enum FlagBits

{

BitCopy=1,

BitOwn=2

};

};

m_begin,m_end,m_iter表示元素位置

三.Next实现

template [span style="color: rgba(0, 0, 255, 1)">class Base, const IID piid, class T, class Copy>

STDMETHODIMP CComEnumImpl::Next(

In ULONG celt,

Out T rgelt,

_Outopt ULONG pceltFetched)

{

if (pceltFetched != NULL)

pceltFetched = 0;

if (rgelt == NULL || (celt > 1 && pceltFetched == NULL))

return E_POINTER;

if (m_begin == NULL || m_end == NULL || m_iter == NULL)

return E_FAIL;

ULONG nRem = (ULONG)(m_end - m_iter);

HRESULT hRes = S_OK;

if (nRem < celt)

hRes = S_FALSE;

ULONG nMin = celt < nRem ? celt : nRem ;

if (pceltFetched != NULL)

pceltFetched = nMin;

T pelt = rgelt;

while(nMin--)

{

HRESULT hr = Copy::copy(pelt, m_iter);

if (FAILED(hr))

{

while (rgelt < pelt)

Copy::destroy(rgelt++);

if (pceltFetched != NULL)

pceltFetched = 0;

return hr;

}

pelt++;

m_iter++;

}

return hRes;

}

关键部分在于Copy::copy和Copy::destroy方法,所以拷贝策略在于外部的Copy类的的静态方法copy

四.拷贝策略类

template [span style="color: rgba(0, 0, 255, 1)">class T>

class _Copy

{

public:

static HRESULT copy(Out T p1, In const T p2)

{

Checked::memcpy_s(p1, sizeof(T), p2, sizeof(T));

return S_OK;

}

static void init(_Inoutopt T)

{

}

static void destroy(_Inoutopt T)

{

}

};

除此之外,还提供了一些常用的特化类

五.CComEnum类

template [span style="color: rgba(0, 0, 255, 1)">class Base, const IID piid, class T, class Copy, class ThreadModel = CComObjectThreadModel>

class ATL_NO_VTABLE CComEnum :

public CComEnumImpl,

public CComObjectRootEx

{

public:

typedef CComEnum _CComEnum;

typedef CComEnumImpl _CComEnumBase;

//代码效果参考：http://www.zidongmutanji.com/bxxx/52900.html

COM_INTERFACE_ENTRY_IID(*piid, _CComEnumBase)

END_COM_MAP()

};

如上,所以要所以CComEnum 的话，需如下定义

typedef CComEnum< IEnumVARIANT, &IID_IEnumVARIANT, VARIANT,

_Copy > CComEnumVariant;