Passing a method pointer from C # to Delphi DLL

Question

I had some problems with passing a string since PChar for Delphi built a DLL and resolved it thanks to Jens Mühlenhoff.

Now I have one more problem -

I made a successful call to the C # method when passing to a DLL if the Delphi declaration is a regular type procedure, but if the Delphi declaration is a method type procedure, I get the error message "Attempting to read or write protected memory".

I tried searching ...

Here is the Delphi declaration

TCallBack = procedure ( s : String) of object;stdcall; 

Here is the C # code

 [DllImport( "DLLTest.dll", CallingConvention = CallingConvention.StdCall, CharSet = CharSet.Ansi, EntryPoint = "DLL_Test" )] public static extern void DLL_Test(IntPtr p, [MarshalAs(UnmanagedType.LPStr)] string Location, int AIntValue); public delegate void MethodCallBackEvent(string s); public event MethodCallBackEvent Info; public void GetInfo(string s) { MessageBox.Show("Info: " + s); } 

used as

  Info = GetInfo; //or Info = new MethodCallBackEvent(GetInfo); IntPtr p = Marshal.GetFunctionPointerForDelegate(Info); DLL_Test(p, "location message", 10); 

Answer 1

Here is a working example. DllTest1 uses a regular function callback. DllTest2 expects a callback as a direct pointer to the C # function (requires a little hack on the Delphi side), and DllTest3 expects a callback pointer as a Delphi method callback (requires a little hack on the C # side).

 // Delphi library test; uses SysUtils; {$R *.res} type TCallback = procedure (P: PChar); stdcall; TMethodCallback = procedure (P: PChar) of object; stdcall; procedure DllTest1(Callback: TCallback; P: PChar; I: Integer); stdcall; var S: string; begin S := Format('DllTest1 ''%s'' %d', [P, I]); if Assigned(Callback) then Callback(PChar(S)); end; procedure DllTest2(_Callback: Pointer; P: PChar; I: Integer); stdcall; var Callback: TMethodCallback absolute _Callback; S: string; begin S := Format('DllTest2 ''%s'' %d', [P, I]); if Assigned(Callback) then Callback(PChar(S)); end; procedure DllTest3(Callback: TMethodCallback; P: PChar; I: Integer); stdcall; var S: string; begin S := Format('DllTest3 ''%s'' %d', [P, I]); if Assigned(Callback) then Callback(PChar(S)); end; exports DllTest1, DllTest2, DllTest3; begin end. // C# using System; using System.Collections.Generic; using System.Text; using System.Runtime.InteropServices; namespace DllTest { class Program { public struct Method { public IntPtr code; public IntPtr data; } [DllImport("Test.dll", CallingConvention = CallingConvention.StdCall, CharSet = CharSet.Ansi, EntryPoint = "DllTest1")] public static extern void DllTest1(IntPtr p, [MarshalAs(UnmanagedType.LPStr)] string s, int i); [DllImport("Test.dll", CallingConvention = CallingConvention.StdCall, CharSet = CharSet.Ansi, EntryPoint = "DllTest2")] public static extern void DllTest2(IntPtr p, [MarshalAs(UnmanagedType.LPStr)] string s, int i); [DllImport("Test.dll", CallingConvention = CallingConvention.StdCall, CharSet = CharSet.Ansi, EntryPoint = "DllTest3")] public static extern void DllTest3(Method m, [MarshalAs(UnmanagedType.LPStr)] string s, int i); public delegate void Callback([MarshalAs(UnmanagedType.LPStr)] string s); public delegate void MethodCallback(IntPtr self, [MarshalAs(UnmanagedType.LPStr)] string s); public static void ShowInfo(string s) { Console.WriteLine("Info: " + s); } public static void ShowMethodInfo(IntPtr self, string s) { Console.WriteLine("Info: " + s); } static void Main(string[] args) { Method m; Callback info = ShowInfo; MethodCallback methodInfo = ShowMethodInfo; IntPtr p = Marshal.GetFunctionPointerForDelegate(info); IntPtr pm = Marshal.GetFunctionPointerForDelegate(methodInfo); // function callback example DllTest1(p, "test", 42); // method callback example 1 DllTest2(pm, "test", 42); // method callback example 2 m.code = pm; m.data = IntPtr.Zero; DllTest3(m, "test", 42); } } }