Fwd: accessing wrapped data

Hi there,

First of all, I do apologize, if I have sent this before, but I am unsure,
that my message actually arrived at the mailing list.

I have a data struct from C++:

struct UiData
{
    double temperature;
}
, for which swig has generated a C# wrapper, UiData.cs. This generated
wrapper is part of a dll and I have a question on how to access it, when
dealing with callbacks.

I have defined a function that takes a callback with said struct as an
arguement in C++ that looks like this:

typedef void(_stdcall *uiDataObserverFunc)(UiData*);
__declspec(dllexport) void UI_RegisterObserver(uiDataObserverFunc
callbackFunc);

and a C# callback signature that looks like this:

    [UnmanagedFunctionPointer(CallingConvention.StdCall)]
    public delegate void PureCallbackData(UiData data);

    [DllImport("PureCppDll", EntryPoint = "UI_RegisterObserver")]
    public static extern void
RegisterObserverData([MarshalAs(UnmanagedType.FunctionPtr)]
PureCallbackData callbackPointer);

The actual callback function is this:

PureManagedDll.PureCallbackData cbfred = (UiData data) =>
            {
                Console.WriteLine("hello from the RegisterObserverData
func: {0}", data.temperature);
            };
PureManagedDll.RegisterObserverData(cbfred);

I don't know why, but at this point I get no output at all, and if I go
into the debugger of VisualStudio I get an access violation. Am I doing
something completely absurd? I also tried using a ref UiData with the
callback, but the result is the same.
In a previous version of my test project, I had no separation between the
wrapper and the test program, so I used

 internal UiData(global::System.IntPtr cPtr, bool cMemoryOwn)

and a callback that would take an IntPtr to achieve my goal. But this is no
longer possible, when the wrapped code is in a separate DLL, so I am pretty
much stuck.

if anyone knows how to do this, please help. I have no idea, what the
problem is.

Br,
Fred

P.S. If you want, I can provide a buildable VisualStudio project and the
swig project file for my dilemma.

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