Receiving an object in a unmanaged callback function
- by Daniel Baulig
Eg. I have following delegate method I want to use as a callback function with unmanaged code:
public delegate void Callback(IntPtr myObject);
Callback callback;
I register it in the following way:
[DllImport("a.dll")]
public static void registerCallback(IntPtr callbackFunction, IntPtr anObject);
// ...
this.myObject = new MyClass();
this.objectPin = GCHandle.Alloc(this.myObject, GCHandleType.Pinned);
registerCallback(Marshal.GetFunctionPointerForDelegate(callback), objectPin.AddrOfPinnedObject());
Now whenever the callback function is called it will have a Pointer/Handle of an object of the MyClass class. I could use Marshal.PtrToStructure to convert this to an object of MyClass. However, what I would like to have is that the delegate definition already contains the class MyClass. eg.:
public delegate void Callback(MyClass myObject);
I tried this, but it will not work. I also tried the following, which did not work:
public delegate void Callback([MarshalAs(UnmanagedType.IUnknown)]MyClass myObject);
I suppose I would need something like "UnmarshalAs" at this point, but sadly this is not available. Any suggestions how I could get lost of that IntPtr in my callback function and get a it packed up as a regular, managed MyClass object?
