C# 4 and .NET 4

722 ❘ ChaPTer 26 interOp
The main method now needs a change to advise the component of the existence of the event sink object,
so that the component can call back into the sink. This can be done with the method DispEventAdvise()
of the CEventHandler class by passing an IUnknown interface pointer. The method DispEventUnadvise()
unregisters the sink object again.
int _tmain(int argc, _TCHAR* argv[])
{
HRESULT hr;
hr = CoInitialize(NULL);
try
{
IWelcomePtr spWelcome;
hr = spWelcome.CreateInstance("Wrox.DotnetComponent");
IUnknownPtr spUnknown = spWelcome;
cout < < spWelcome- > Greeting("Bill") < < endl;
CEventHandler* eventHandler = new CEventHandler();
hr = eventHandler- > DispEventAdvise(spUnknown);
IMathPtr spMath;
spMath = spWelcome; // QueryInterface()
long result = spMath- > Add(4, 5);
cout < < "result:" < < result < < endl;
eventHandler- > DispEventUnadvise(spWelcome.GetInterfacePtr());
delete eventHandler;
}
catch (_com_error& e)
{
cout < < e.ErrorMessage() < < endl;
}
}
CoUninitialize();
return 0;
PlaTform inVoKe
Not all the features of Windows API calls are available from the .NET Framework. This is not only true
for old Windows API calls but also for very new features from Windows 7 or Windows Server 2008 R2.
Maybe you ’ ve written some DLLs that export unmanaged methods, and you would like to use them from
C# as well.
You can read about specifi c features of Windows 7 and Windows Server 2008 R2 in
Appendix A, “Guidelines for Windows 7 and Windows Server 2008 R2.”
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