C++/CLI managed class member callback by managed code - delegates

Question

I am designing a class in C++/CLR that uses a callback function provided by user code.
This works very nicely if the callback function is free ( i.e. not the member of a class ). It is almost the same as in pure C++.
Here is some sample code that works well:
ref class ClassThatUsesCallback
{
public:
typedef void (*callback_t)( String^ );
void setCallback( callback_t pfun )
{
myCallback = pfun;
}
void Run()
{
if( myCallback != nullptr ) {
myCallback("This is a test");
}
}
private:
callback_t myCallback;
};
void FreeFunction( String^ s )
{
Console::WriteLine( "Free Function Callback " + s );
}
int main(array<System::String ^> ^args)
{
ClassThatUsesCallback^ theClassThatUsesCallback
= gcnew ClassThatUsesCallback();
theClassThatUsesCallback->setCallback( FreeFunction );
theClassThatUsesCallback->Run();
}
However, I would like the callbacked function to be a member of a class in the user code ( so it can make use of and change the attributes of the user code class )
The following code does not compile
ref class ClassThatProvidesCallback
{
public:
void MemberFunction( String^ s )
{
Console::WriteLine( "Member Function Callback " + s );
}
void Run()
{
ClassThatUsesCallback^ theClassThatUsesCallback
= gcnew ClassThatUsesCallback();
theClassThatUsesCallback->setCallback(
&ClassThatProvidesCallback::MemberFunction );
theClassThatUsesCallback->Run();
}
};
I get this error
error C3374: can't take address of 'ClassThatProvidesCallback::MemberFunction'
unless creating delegate instance
When I research this, I find numerous explanations of how to call un-managed code from managed code ( and vice-versa ) I do not need to do this - all the code involved is managed. So I am hoping that someone can point me to a simple way to this.

Answer 1

This is full solution:
ref class ClassThatUsesCallback
{
public:
void setCallback( Action<String^>^ callback )
{
myCallback = callback;
}
void Run()
{
if( myCallback != nullptr ) {
myCallback("This is a test");
}
}
private:
Action<String^>^ myCallback;
};
ref class ClassThatProvidesCallback
{
public:
void MemberFunction( String^ s )
{
Console::WriteLine( "Member Function Callback " + s );
}
void Run()
{
ClassThatUsesCallback^ theClassThatUsesCallback
= gcnew ClassThatUsesCallback();
theClassThatUsesCallback->setCallback(gcnew Action<String^>(this,
&ClassThatProvidesCallback::MemberFunction));
theClassThatUsesCallback->Run();
}
};
int main(array<System::String ^> ^args)
{
ClassThatProvidesCallback^ c = gcnew ClassThatProvidesCallback();
c->Run();
return 0;
}
Native C++ style typedef is replaced with .NET Action delegate. Additional parameter this is added to setCallback call, it is required to define the class instance which contains the callback function.