Atl笔记二:BEGIN_COM_MAP-创新互联
1,offsetofclass
获取基类相对于子类的偏移位置。
#define _ATL_PACKING 8
#define
offsetofclass(base, derived) ((DWORD_PTR)(static_cast
_ATL_PACKING非零就行,只是作为一个地址。因为为了避免虚类无法创建对象的问题所以没有通过类对象来计算。
2,
//If you get a message that FinalConstruct is ambiguous then you need to
// override it in your class and call each base class' version of this
#define BEGIN_COM_MAP(x) public:
typedef x _ComMapClass;
IUnknown* _GetRawUnknown() throw()
{ ATLASSERT(_GetEntries()[0].pFunc == _ATL_SIMPLEMAPENTRY); return (IUnknown*)((INT_PTR)this+_GetEntries()->dw); }
_ATL_DECLARE_GET_UNKNOWN(x)
HRESULT _InternalQueryInterface(REFIID iid, void** ppvObject) throw()
{ return InternalQueryInterface(this, _GetEntries(), iid, ppvObject); }
const static ATL::_ATL_INTMAP_ENTRY* WINAPI _GetEntries() throw() {
static const ATL::_ATL_INTMAP_ENTRY _entries[]= { DEBUG_QI_ENTRY(x)
struct _ATL_INTMAP_ENTRY
{
const IID* piid; // the interface id (IID)
DWORD_PTR dw;
_ATL_CREATORARGFUNC* pFunc; //NULL:end, 1:offset, n:ptr
};
#define DEBUG_QI_ENTRY(x)
{NULL,
(DWORD_PTR)_T(#x),
(ATL::_ATL_CREATORARGFUNC*)0},
typedef HRESULT (WINAPI _ATL_CREATORARGFUNC)(void* pv, REFIID riid, LPVOID* ppv, DWORD_PTR dw);
#define COM_INTERFACE_ENTRY(x)
{&_ATL_IIDOF(x),
offsetofclass(x, _ComMapClass),
_ATL_SIMPLEMAPENTRY},
#define _ATL_IIDOF(x) __uuidof(x)
//__uuidof获取与x相关的GUID值
#define _ATL_SIMPLEMAPENTRY ((ATL::_ATL_CREATORARGFUNC*)1)
#define END_COM_MAP()
__if_exists(_GetAttrEntries) {{NULL, (DWORD_PTR)_GetAttrEntries, _ChainAttr }, }
{NULL, 0, 0}}; return &_entries[1];}
virtual ULONG STDMETHODCALLTYPE AddRef( void) throw() = 0;
virtual ULONG STDMETHODCALLTYPE Release( void) throw() = 0;
STDMETHOD(QueryInterface)(REFIID, void**) throw() = 0;
3,
static HRESULT WINAPI CComObjectRootBase ::InternalQueryInterface(void* pThis,
const _ATL_INTMAP_ENTRY* pEntries, REFIID iid, void** ppvObject)
{
ATLASSERT(pEntries->pFunc == _ATL_SIMPLEMAPENTRY);
HRESULT hRes =AtlInternalQueryInterface(pThis, pEntries, iid, ppvObject);
return _ATLDUMPIID(iid, pszClassName, hRes);
}
// QI support
ATLINLINE ATLAPIAtlInternalQueryInterface(
_Inout_ void* pThis,
_In_ const _ATL_INTMAP_ENTRY* pEntries,
_In_ REFIID iid,
_COM_Outptr_ void** ppvObject)
{
// First entry in the com map should be a simple map entry
ATLASSERT(pEntries->pFunc == _ATL_SIMPLEMAPENTRY);
if (InlineIsEqualUnknown(iid)) // use first interface
{
IUnknown* pUnk = (IUnknown*)((INT_PTR)pThis+pEntries->dw);
pUnk->AddRef();
*ppvObject = pUnk;
return S_OK;
}
HRESULT hRes;
for (;; pEntries++)
{
if (pEntries->pFunc == NULL)
{
hRes = E_NOINTERFACE;
break;
}
BOOL bBlind = (pEntries->piid == NULL);
if (bBlind || InlineIsEqualGUID(*(pEntries->piid), iid))
{
if (pEntries->pFunc == _ATL_SIMPLEMAPENTRY) //offset
{
ATLASSERT(!bBlind);
IUnknown* pUnk = (IUnknown*)((INT_PTR)pThis+pEntries->dw);
pUnk->AddRef();
*ppvObject = pUnk;
return S_OK;
}
// Actual function call
hRes = pEntries->pFunc(pThis,
iid, ppvObject, pEntries->dw);
if (hRes == S_OK)
return S_OK;
if (!bBlind && FAILED(hRes))
break;
}
}
*ppvObject = NULL;
return hRes;
}
CComObjectRootBase的InternalQueryInterface内部调用AtlInternalQueryInterface遍历_ATL_INTMAP_ENTRY数组(包含所有实现接口的映射表),找到基类的虚函数表返回。
(我原来用的VS2005,没有AtlInternalQueryInterface的实现,蛋疼了好久这个接口映射表的怎么返回的,我猜也是遍历但是没有看见源码一直心头惴惴不安。后面擦查看VS2013里面给出了AtlInternalQueryInterface的实现才把这口气舒出来。)
4,
ATL提供了BEGIN_COM_MAP、END_COM_MAP、COM_INTERFACE_ENTRY与COM_INTERFACE_ENTRY2这4个宏来创建接口映射表。
假设一个类CClassA继承了接口IIntA1和IIntA2,则该类的接口映射表创建如下:
class CClassA : public CComObjectRootEx
{
BEGIN_COM_MAP(CClassA)
COM_INTERFACE_ENTRY(IIntA1)
COM_INTERFACE_ENTRY(IIntA2)
END_COM_MAP()
......
};
static const ATL::_ATL_INTMAP_ENTRY _entries[] =
{
{NULL, (DWORD_PTR)_T(#x), (ATL::_ATL_CREATORARGFUNC*)0},
{& __uuidof(IIntA1),offsetofclass(IIntA1,
CClassA), (ATL::_ATL_CREATORARGFUNC*)1},
{& __uuidof(IIntA2),offsetofclass(IIntA2,
CClassA), (ATL::_ATL_CREATORARGFUNC*)1},
{NULL, 0, 0}
};
而当CClassB继承了IIntB1和IIntB2,并且IIntB1和IIntB2都继承自IDispatch接口。
此时,如果客户程序在查询IDispatch接口,QueryInterface所返回的IDispatch接口指针将无法确定其属于IIntB1还是IIntB2。
在这种情况下,需要指定IDispatch接口指针的默认指向。 COM_INTERFACE_ENTRY2()宏即是用于完成该功能。
下面代码将对IDispatch接口的请求默认指向属于IIntB2的IDispatch接口指针。
class CClassB : public CComObjectRootEx
{
BEGIN_COM_MAP(CClassB)
COM_INTERFACE_ENTRY(IIntB1)
COM_INTERFACE_ENTRY(IIntB2)
COM_INTERFACE_ENTRY2(IDispatch, IIntB2)
END_COM_MAP()
......
};
#define COM_INTERFACE_ENTRY2(x, x2)
{&_ATL_IIDOF(x),
reinterpret_cast
_ATL_SIMPLEMAPENTRY},
5,总结:
BEGIN_COM_MAP通过一个静态的_GetEntries()方法,来获取在该方法中创建的一个静态COM接口映射表。
文章名称:Atl笔记二:BEGIN_COM_MAP-创新互联
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