activex控件 InvokeHelper

当你调用关于activex控件中的相关方法时，你要导入此控件到程序中，此时就会在工程中生成一个关于此控件调用的一个伪调用类，其中的cpp中调用每 个方法都是通过InvokeHelper调用其中的dwDispID值来定位方法的地址的！因此，可以将InvokeHelper调用理解为定位 activex控件中的相关方法的一种手段 ！

invokehelper:   用于调用OLE   的IDispatch   接口方法的一个封装方法。

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.