PRB: Use IDispatch for Objects Created by a DataSpace Object (178845)
The information in this article applies to:
- Remote Data Service for ADO 1.5
- Remote Data Service for ADO 2.0
- Remote Data Service for ADO 2.1
- Remote Data Service for ADO 2.5
- Remote Data Service for ADO 2.6
This article was previously published under Q178845 SYMPTOMS
Remote Data Services (RDS) has a DataSpace object that creates COM objects
on a remote Internet Information Server (IIS) computer. The DataSpace's
CreateObject() call accepts a ProgID as well as the Universal Resource
Identifier (URL) for an IIS server. CreateObject() returns a variant that
contains the IDispatch * for the created object.
If QueryInterface() is called to get an interface other than IDispatch,
E_NOINTERFACE is returned.
CAUSE
All calls to methods of the object created by DataSpace.CreateObject() must
be made through IDispatch::Invoke(). Furthermore, you must call
GetIDsOfNames() to get the DISPIDs of the methods you want to call because
RDS changes the values of the DISPIDs. They may be different from the IDs
specified in the typelib.
RESOLUTION
The Visual C++ code sample shown below in the "More Information" section
demonstrates how to call methods of a remote object created with RDS. The
sample uses the Visual C++ 5.0 #import feature to generate C++ classes for
calling methods of the DataSpace object and the remote object, which in
this case is an RDS DataFactory.
The sample code shows calling the undocumented function
_com_dispatch_method(), which is a function of the C run-time library. As
an alternative, IDispatch::Invoke can be called directly without the use of
this helper function.
Here is a short description of the function:
HRESULT __cdecl _com_dispatch_method(IDispatch * pDisp, DISPID dispid,
WORD w, VARTYPE vt, void * pResult, const wchar_t * szFormat,
...);
pDisp - IDispatch of the method's object.
dispid - The DISPID of the method to call.
w - Always DISPATCH_METHOD.
vt - The return type. Must be a Variant type.
pResult - Pointer to the memory location to place the return value.
SzFormat - String where each byte represents the variant type of each
of the arguments being passed to the method.
The method contains a variable number of arguments because szFormat is
followed by the arguments that you are passing to the object's method.
STATUS
This behavior is by design.
MORE INFORMATION
| Modification Type: | Minor | Last Reviewed: | 3/14/2005 |
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| Keywords: | kbcode kbDatabase kbprb KB178845 |
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