activex控制項 InvokeHelper

當你調用關於activex控制項中的相關方法時，你要匯入此控制項到程式中，此時就會在工程中產生一個關於此控制項調用的一個偽調用類，其中的cpp中調用每
個方法都是通過InvokeHelper調用其中的dwDispID值來定位方法的地址的！因此，可以將InvokeHelper調用理解為定位
activex控制項中的相關方法的一種手段
！

invokehelper:   用於調用OLE   的IDispatch   介面方法的一個封裝方法。

CWnd::InvokeHelper

Call this member function to invoke the ActiveX Control method or property specified by dwDispID
, in the context specified by wFlags
.

void AFX_CDECL InvokeHelper(
   DISPID dwDispID,
   WORD wFlags,
   VARTYPE vtRet,
   void* pvRet,
   const BYTE* pbParamInfo,
   ... 
);

Parameters

dwDispID

Identifies the method or property to be invoked.

wFlags

Flags describing the context of the call to IDispatch::Invoke
. For possible wFlags
values, see IDispatch::Invoke
in the Platform SDK
.

vtRet

Specifies the type of the return value. For possible values, see the Remarks section for COleDispatchDriver::InvokeHelper
.

pvRet

Address of the variable that will that will receive the property value or return value. It must match the type specified by vtRet
.

pbParamInfo

Pointer to a null-terminated string of bytes specifying the types of the parameters following pbParamInfo
. For possible values, see the Remarks section for COleDispatchDriver::InvokeHelper
.

...

Variable List of parameters, of types specified in pbParamInfo
.

Remarks

The pbParamInfo
parameter specifies the types of the parameters passed to the method or
property. The variable list of arguments is represented by ...
in the syntax declaration.

This function converts the parameters to VARIANTARG
values, then invokes the IDispatch::Invoke
method on the ActiveX control. If the call to IDispatch::Invoke
fails, this function will throw an exception. If the SCODE
(status code) returned by IDispatch::Invoke
is DISP_E_EXCEPTION
, this function throws a COleException
object, otherwise it throws a COleDispatchException
.

Note
   This function should be called only on a CWnd
object that represents an ActiveX control.

For
more information about using this member function with ActiveX Control
Containers, see the article ActiveX Control Containers: Programming
ActiveX Controls in an ActiveX Control Container.