Unmanaged Exports and delegates

Question

I am using Robert Giesecke Unmanaged Exports to create a .NET wrapper DLL to use a .NET DLL in Delphi 7. Everything works fine so far, but now I have a function which needs to have a callback/delegate.

How can this be done?

Can I just give the function pointer to my .NET DLL and call it from there and when yes how is it done?

Answer 1

It's pretty simple. You define a delegate type just as you would with a standard p/invoke.

Here's the simplest example that I can think of:

C#

using RGiesecke.DllExport;

namespace ClassLibrary1
{
    public delegate int FooDelegate();

    public class Class1
    {
        [DllExport()]
        public static int Test(FooDelegate foo)
        {
            return foo();
        }
    }
}

Delphi

program Project1;

{$APPTYPE CONSOLE}

type
  TFooDelegate = function: Integer; stdcall;

function Test(foo: TFooDelegate): Integer; stdcall; external 'ClassLibrary1.dll';

function Func: Integer; stdcall;
begin
  Result := 666;
end;

begin
  Writeln(Test(Func));
end.

Output

666

The default calling convention on the C# side is CallingConvention.Stdcall so I've gone along with that. That's the obvious thing to do.