一个MFC宏实现COM接口的问题
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1. 问题提出:
《COM原理与应用》中的第五章的例子中的INIT_INTERFACE_PART(CDictionary, Dictionary) INIT_INTERFACE_PART(CDictionary, Dictionary) STDMETHOD_(BOOL, Initialize)(); STDMETHOD_(BOOL, LoadLibrary)(LPOLESTR); STDMETHOD_(BOOL, InsertWord)(LPOLESTR, LPOLESTR); STDMETHOD_(void, DeleteWord)( LPOLESTR); STDMETHOD_(BOOL, LookupWord)(LPOLESTR, LPOLESTR *); STDMETHOD_(BOOL, RestoreLibrary)(LPOLESTR); STDMETHOD_(void, FreeLibrary)(); END_INTERFACE_PART_STATIC(Dictionary) 2.候sir说过:“源码面前了无秘密”。看看这些宏定义的源代码: #define BEGIN_INTERFACE_PART(localClass, baseClass) \ //这个宏在代码中插入如下代码一看就知道声明了IUnknown的三个方法 class X##localClass : public baseClass \ { \ public: \ STDMETHOD_(ULONG, AddRef)(); \ STDMETHOD_(ULONG, Release)(); \ STDMETHOD(QueryInterface)(REFIID iid, LPVOID* ppvObj); \ #ifndef _AFX_NO_NESTED_DERIVATION //这里进行了判断,所以有时候不要也可以,最好要 #define INIT_INTERFACE_PART(theClass, localClass) \ size_t m_nOffset; \ //纪录指针偏移量 X##localClass() \ #define INIT_INTERFACE_PART(theClass, localClass) 看了源码,其实我们已经可以清楚这些宏到底做了些什么。 1 首先你上面的问题: baseClass:是指接口类IDictionary 好,再结合一个msdn的例子: class CPrintEditObj : public CCmdTarget { public: protected: STDMETHOD_(void, EditObject)(); STDMETHOD_(void, PrintObject)(); END_INTERFACE_PART(PrintObj) }; 在这个例子中CPrintEditObj是嵌套类,实现了两个接口IEditInterface和IPrintInterface,而: BEGIN_INTERFACE_PART(EditObj,IEditInterface) 实现了IEditInterface接口 BEGIN_INTERFACE_PART(PrintObj, IPrintInterface) 实现了IPrintInterface接口 宏源码中的: #define INIT_INTERFACE_PART_DERIVE(theClass, localClass) \ X##localClass() \ { m_nOffset = offsetof(theClass, m_x##localClass); } \ 纪录下了m_x EditObj和m_x PrintObj与包容类CPrintEditObj的地址偏移。以便在通过CPrintEditObj嵌套类查询IEditInterface 和IPrintInterface接口的时候能返回正确的接口指针。
DictionaryObj.h 文件中有以下宏定義:
BEGIN_INTERFACE_PART(Dictionary, IDictionary)
#define INIT_INTERFACE_PART_DERIVE(theClass, localClass) \
#else
#endif
就以原例说明:
localClass:是指实现当前接口IDictionary的嵌套类
theClass:这个才是真正实现接口的嵌套类!
// Interface Maps
BEGIN_INTERFACE_PART(EditObj, IEditInterface)
BEGIN_INTERFACE_PART(PrintObj, IPrintInterface)
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