Calling C# method from C++ code in WP8 - windows-phone-8

Question

I'm interested in calling a C# method from C++ code in Windows Phone 8. I have already learned how to pass a callback function to C++ code from C# via delegate declarations in my C++ code, but I am looking to see if I can do any of the following:
Call certain methods directly from the C++ code. This would involve somehow inspecting the C# object makeup from C++, and seems unlikely to me, but I thought I'd ask you all anyway
Trigger events in the C# code, which can then be handled by C# methods
Use a dispatcher to call C# callbacks in the Main UI thread so that the callbacks can modify UI elements
Use a dispatcher to trigger events in the C# code, (Essentially a merging of the above two points)
In short, I am looking for as many C++ -->C# communication tips as you guys can throw me, I want to learn it all. :)

Answer 1

By getting an object in C# code to implement a Windows RT interface, and passing down a reference to this object, it is possible to do all of the above with a bit of set-up (if I understand correctly - not sure about exactly what you want to do with your Dispatcher examples - you might want to wrap the Dispatcher on the C# side).
Create a Windows Runtime component library.
Define a public interface class in a C++/CX header for the C# to implement (C++ to call) (e.g. ICallback).
Define a public ref class in a C++/CX header for the C++ to implement (C# to call) (e.g. CppCxClass).
Add a method in CppCxClass that passes and stores an ICallback. (A C++ global variable is shown for consiseness, I recommend you review this to see if you can find a better place to store this in your code-base).
ICallback^ globalCallback;
...
void CppCxClass::SetCallback(ICallback ^callback)
{
globalCallback = callback;
}
Reference the WinRT library in your C# code.
C# code: create an instance of CppCxClass using var cppObject = new CppCxClass().
C# code: create a class which implements ICallback (e.g. CSharpCallbackObject).
C# code: pass an instance of CSharpCallbackObject down to C++. E.g. cppObject.SetCallback(new CSharpCallbackObject()).
You can now call C# with globalCallback->CallCsharp(L"Hello C#");. You should be able to extend either ICallback and/or CppCxObject to do the rest of your tasks.

Answer 2

After a lot of headaches trying to figure out the required code, I think it's worth posting the final version here
C++/CX
//.h
[Windows::Foundation::Metadata::WebHostHidden]
public interface class ICallback
{
public:
virtual void Exec( Platform::String ^Command, Platform::String ^Param);
};
//.cpp
ICallback ^CSCallback = nullptr;
void Direct3DInterop::SetCallback( ICallback ^Callback)
{
CSCallback = Callback;
}
//...
if (CSCallback != nullptr)
CSCallback->Exec( "Command", "Param" );
C#
public class CallbackImpl : ICallback
{
public void Exec(String Command, String Param)
{
//Execute some C# code, if you call UI stuff you will need to call this too
//Deployment.Current.Dispatcher.BeginInvoke(() => {
// //Lambda code
//}
}
}
//...
CallbackImpl CI = new CallbackImpl();
D3DComponent.SetCallback( CI);