C++ COM中IDispatch之Invoke获取对象时，注意点 COM

DISPATCH_PROPERTYGET

The member is retrieved as a property or data member.
这是本文最关键的地址，如果你返回的值是一个COM对象，调用者会增加AddRef吗?不会，所以你需要自己添加计数，否则程序将很快崩溃

补充一条，js脚本在从C++本地语言获取对象时，IE js引擎的做法是，不会记住改对象地址，而是下次要用时重新取，这也就更需要注意引用计数这个问题了

Provides access to properties and methods exposed by an object. The dispatch function DispInvoke provides a standard implementation of Invoke.
Syntax C++

HRESULT Invoke( [in]DISPID dispIdMember, [in]REFIID riid, [in]LCID lcid, [in]WORD wFlags, [in, out]DISPPARAMS *pDispParams, [out]VARIANT *pVarResult, [out]EXCEPINFO *pExcepInfo, [out]UINT *puArgErr );

Parameters

dispIdMember [in]

Identifies the member. Use GetIDsOfNames or the object's documentation to obtain the dispatch identifier.

riid [in]

Reserved for future use. Must be IID_NULL.

lcid [in]

The locale context in which to interpret arguments. The lcid is used by the GetIDsOfNames function, and is also passed to Invoke to allow the object to interpret its arguments specific to a locale.
Applications that do not support multiple national languages can ignore this parameter. For more information, refer to Supporting Multiple National Languages and Exposing ActiveX Objects.

wFlags [in]

Flags describing the context of the Invoke call.

Value	Meaning
DISPATCH_METHOD	The member is invoked as a method. If a property has the same name, both this and the DISPATCH_PROPERTYGET flag can be set.
DISPATCH_PROPERTYGET	The member is retrieved as a property or data member. 这是本文最关键的地址，如果你返回的值是一个COM对象，调用者会增加AddRef吗?不会，所以你需要自己添加计数，否则程序将很快崩溃
DISPATCH_PROPERTYPUT	The member is changed as a property or data member.
DISPATCH_PROPERTYPUTREF	The member is changed by a reference assignment, rather than a value assignment. This flag is valid only when the property accepts a reference to an object.

pDispParams [in, out]

Pointer to a DISPPARAMS structure containing an array of arguments, an array of argument DISPIDs for named arguments, and counts for the number of elements in the arrays.

pVarResult [out]

Pointer to the location where the result is to be stored, or NULL if the caller expects no result. This argument is ignored if DISPATCH_PROPERTYPUT or DISPATCH_PROPERTYPUTREF is specified.

pExcepInfo [out]

Pointer to a structure that contains exception information. This structure should be filled in if DISP_E_EXCEPTION is returned. Can be NULL.

puArgErr [out]

The index within rgvarg of the first argument that has an error. Arguments are stored in pDispParams->rgvarg in reverse order, so the first argument is the one with the highest index in the array. This parameter is returned only when the resulting return value is DISP_E_TYPEMISMATCH or DISP_E_PARAMNOTFOUND. This argument can be set to null. For details, see Returning Errors.

Return value This method can return one of these values.

Return code	Description
S_OK	Success.
DISP_E_BADPARAMCOUNT	The number of elements provided to DISPPARAMS is different from the number of arguments accepted by the method or property.
DISP_E_BADVARTYPE	One of the arguments in DISPPARAMS is not a valid variant type.
DISP_E_EXCEPTION	The application needs to raise an exception. In this case, the structure passed in pexcepinfo should be filled in.
DISP_E_MEMBERNOTFOUND	The requested member does not exist.
DISP_E_NONAMEDARGS	This implementation of IDispatch does not support named arguments.
DISP_E_OVERFLOW	One of the arguments in DISPPARAMS could not be coerced to the specified type.
DISP_E_PARAMNOTFOUND	One of the parameter IDs does not correspond to a parameter on the method. In this case, puArgErr is set to the first argument that contains the error.
DISP_E_TYPEMISMATCH	One or more of the arguments could not be coerced. The index of the first parameter with the incorrect type within rgvarg is returned inpuArgErr.
DISP_E_UNKNOWNINTERFACE	The interface identifier passed in riid is not IID_NULL.
DISP_E_UNKNOWNLCID	The member being invoked interprets string arguments according to the LCID, and the LCID is not recognized. If the LCID is not needed to interpret arguments, this error should not be returned
DISP_E_PARAMNOTOPTIONAL	A required parameter was omitted.

Remarks Generally, you should not implement Invoke directly. Instead, use the dispatch interface to create functionsCreateStdDispatch and DispInvoke. For details, refer to CreateStdDispatch, DispInvoke, Creating the IDispatch Interface and Exposing ActiveX Objects.
If some application-specific processing needs to be performed before calling a member, the code should perform the necessary actions, and then call ITypeInfo::Invoke to invoke the member. ITypeInfo::Invoke acts exactly like Invoke. The standard implementations of Invoke created by CreateStdDispatch and DispInvokedefer to ITypeInfo::Invoke.
In an ActiveX client, Invoke should be used to get and set the values of properties, or to call a method of an ActiveX object. The dispIdMember argument identifies the member to invoke. The DISPIDs that identify members are defined by the implementor of the object and can be determined by using the object's documentation, the IDispatch::GetIDsOfNames function, or the ITypeInfo interface.
When you use IDispatch::Invoke() with DISPATCH_PROPERTYPUT or DISPATCH_PROPERTYPUTREF, you have to specially initialize the cNamedArgs and rgdispidNamedArgs elements of your DISPPARAMS structure with the following:
C++

DISPID dispidNamed = DISPID_PROPERTYPUT; dispparams.cNamedArgs = 1; dispparams.rgdispidNamedArgs = &dispidNamed;

The information that follows addresses developers of ActiveX clients and others who use code to expose ActiveX objects. It describes the behavior that users of exposed objects should expect.
Requirements