Passing a method pointer in parameter to a DLL

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Hello,
That is my problem: I have a DLL written in C++ that I try to reporting in C#.
So I created a class that contains methods exported from the DLL:

C#

using System.Runtime.InteropServices;
 
namespace MyDLL
{
  public class myDLL
  {
    /// <summary>
    /// Changing window title.
    /// </summary>
    [DllImport("MyDLL.dll")]
    public static extern bool WndSetTitle(IntPtr hWnd,
      [MarshalAs(UnmanagedType.LPStr)] string pTitle);
  }
}

The problem is that this DLL must reporting a method of the main program. There is therefore a method parameter receives a pointer to this method.
The class code should look like this:

C#

using System.Runtime.InteropServices;
 
namespace MyDLL
{
  public class myDLL
  {
    /// <summary>
    /// Sending the pointer to the method to be executed by the DLL.
    /// </summary>
    [DllImport("MyDLL.dll")]
    public static extern bool SetProcHandler(IntPtr pfMyProc);
  }
}

But I know not how reporting this method by passing in setting one point to another method :sigh: .

For info, function calling code looks like this Pascal:

Pascal

// The exported DLL function declaration
function SetProcHandler(pfMyProc: Pointer): Boolean; stdcall; 
  external 'MyDLL.dll';

// The function to be executed by the DLL Declaration
function MyProc(Prm1, Prm2: Integer): Integer;
begin
  // ...
end;

// Pointer to the function to run sending
SetProcHandler(@MyProc);

So, I hope not to be too confusing in my application :-O .
Thank you in advance for your response.

Posted 19-Feb-10 23:50pm

ILPlais

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ILPlais · Answer 1 · 2010-02-26T09:00:00

I've finally managed to send a pointer to my DLL :).
I am a little inspired me a carousel source code.
My code is something like this:
In the DLL callback's API:

C#

using System.Runtime.InteropServices;
 
namespace MyDLL
{
  public class myDLL
  {
    /// <summary>
    /// Sending the callback method's pointer to the DLL.
    /// </summary>
    [DllImport("MyDLL.dll")]
    public static extern bool SetProcHandler([MarshalAs(UnmanagedType.FunctionPtr)] MyProc pfMyProc);
    
    /// <summary>
    /// Method used for DLL's messages.
    /// </summary>
    [UnmanagedFunctionPointer(CallingConvention.StdCall)]
    public delegate int SendProc(int Prm1, int Prm2);
  }
}

In the main program:

C#

using MyDLL
namespace MyProgram
{
  public partial class Principale : Form
  {
    /// <summary>
    /// Method for DLL's callback
    /// </summary>
    static MyDLL.SendProc myProc = null;
    public Principale()
    {
      InitializeComponent();
      
      myProc = new MyDLL.SendProc(MyProc);
      
      // Sending method to the DLL
      MyDLL.SetProcHandler(myProc);
      
      // Prevents the pointer cleaning
      GC.KeepAlive(myProc);
    }
        
    public unsafe int MyProc(int Prm1, int Prm2)
    {
      return 0;
      // …
    }    
  }
}

I'm still a little test to see if it that generates not errors :~.
I hope that it can still be useful to someone :-D.