C++ Callback to send text back to C#

Question

I\'m new to C++. I have been told using a \"callback\" with C++ is the best solution for this. Here is my situation.

I have a DLL written in C++
this DLL has

Answer 1

There may be cleaner ways, but here are some of the steps I used to make it work.

Define the delegate and the function to pass it to your DLL. The parameters are what will be sent back to the C# delegate:

  public delegate uint CallbackFn( uint param1, uint param2 );

  [DllImport("yourdll.dll",  CallingConvention=CallingConvention.Winapi, EntryPoint="RegisterTheCallback" )]
  private static extern uint RegisterTheCallback( CallbackFn pfn );

Create a variable to store the delegate. Make sure this doesn't go out of scope. In my testing, I found that the GC would reclaim it (it wasn't "aware" that my DLL was still using it):

  CallbackFn mCmdCallback = null;

Then initialize it somewhere:

  mCmdCallback = new CallbackFn( YourCallback );

And then pass it to your DLL:

RegisterTheCallback( mCmdCallback );

And define the actual method that will receive the call:

  private uint YourCallback( uint param1, uint param2 )
  {
    // report progress etc.
  }

The code in the DLL might look like this:

DWORD _declspec( dllexport ) WINAPI RegisterTheCallback
(
   DWORD (WINAPI *lpfnCallback)( DWORD param1, DWORD param2 )
)
{
// Store lpfnCallback somewhere so that it can be called later
...
}

And then the code in your DLL can call it with the appropriate data when it needs:

ret = (lpfnCallback)( 234, 456 );