C# 4 and .NET 4

Using a .neT Component from a CoM Client ❘ 721
The name of the event must be the same as the name of the method inside the source
interface. Otherwise, the events cannot be mapped for COM clients.
Creating a Client with a sink object
After you ’ ve built and registered the .NET assembly and installed it into the global assembly cache, you can
build a client application by using the event sources. Implementing a callback or sink object that implements
the IDispatch interface was — using Visual Basic 6.0 — just a matter of adding the With Events keyword,
very similar to how Visual Basic deals with .NET events today. It ’ s more work with C++, but here the Active
Template Library helps.
Open the C++ Console application created in the section “ Creating a COM Client Application ” and add the
following includes to the fi le stdafx.h :
#include < atlbase.h >
extern CComModule _Module;
#include < atlcom.h >
The fi le stdafx.cpp requires an include of the ATL implementation fi le atlimpl.cpp :
#include < atlimpl.cpp >
code snippet COMClient/stdafx.h
code snippet COMClient/stdafx.cpp
Add the new class CEventHandler to the fi le COMClient.cpp . This class contains the implementation of
the IDispatch interface to be called by the component. The implementation of the IDispatch interface
is done by the base class IDispEventImpl . This class reads the type library to match the dispatch IDs
of the methods and the parameters to the methods of the class. The template parameters of the class
IDispatchEventImpl requires an ID of the sink object (here the ID 4 is used), the class that implements the
callback methods ( CEventHandler ), the interface ID of the callback interface ( DIID_IMathEvents ), the ID
of the type library ( LIBID_DotnetComponent ), and the version number of the type library. You can fi nd the
named IDs DIID_IMathEvents and LIBID_DotnetComponent in the fi le dotnetcomponent.tlh that was
created from the #import statement.
The sink map that is surrounded by BEGIN_SINK_MAP and END_SINK_MAP defi nes the methods that are
implemented by the sink object. SINK_ENTRY_EX maps the method OnCalcCompleted to the dispatch
ID 46200. This dispatch ID was defi ned with the method CalculationCompleted of the IMathEvents
interface in the .NET component.
class CEventHandler: public IDispEventImpl < 4, CEventHandler,
& DIID_IMathEvents, & LIBID_DotnetComponent, 1, 0 >
{
public:
BEGIN_SINK_MAP(CEventHandler)
SINK_ENTRY_EX(4, DIID_IMathEvents, 46200, OnCalcCompleted)
END_SINK_MAP()
HRESULT __stdcall OnCalcCompleted()
{
cout < < "calculation completed" < < endl;
return S_OK;
}
};
code snippet COMClient/COMClient.cpp
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