C#调用Delphi接口(ITest = interface)

首先创建一个delphi的DLL工程

library testintfdll;

{ Important note about DLL memory management: ShareMem must be the
  first unit in your library's USES clause AND your project's (select
  Project-View Source) USES clause if your DLL exports any procedures or
  functions that pass strings as parameters or function results. This
  applies to all strings passed to and from your DLL--even those that
  are nested in records and classes. ShareMem is the interface unit to
  the BORLNDMM.DLL shared memory manager, which must be deployed along
  with your DLL. To avoid using BORLNDMM.DLL, pass string information
  using PChar or ShortString parameters. }

uses
  SysUtils,
  Classes,
  uintf in 'uintf.pas';

{$R *.res}

exports
  GetImpl;

begin
end.

接下来声明并实现接口

unit uintf;

interface

uses Windows;

type
  ITest = interface
    ['{000A0299-A27A-4D35-9721-419AE6E83869}']
    procedure ShowMessage(msg: PAnsiChar); stdcall;
    function Add(a, b: Integer): Integer; stdcall;
  end;

  TTest = class(TInterfacedObject, ITest)
  protected
    procedure ShowMessage(msg: PAnsiChar); stdcall;
    function Add(a, b: Integer): Integer; stdcall;
  end;

procedure GetImpl(out instance: ITest); stdcall;

implementation

procedure GetImpl(out instance: ITest);
begin
  instance := TTest.Create;
end;

{ TTest }

function TTest.Add(a, b: Integer): Integer;
begin
  Result := a + b;
end;

procedure TTest.ShowMessage(msg: PAnsiChar);
begin
  MessageBox(0, msg, 'title', ID_OK);
end;

end.

最后在c#中调用

using System;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Windows.Forms;

namespace CShapeTestClient
{
    [ComVisible(true)]
    [ComImport, Guid("000A0299-A27A-4D35-9721-419AE6E83869"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
    public interface ITest
    {
        [MethodImplAttribute(MethodImplOptions.PreserveSig)]
        void ShowMessage([MarshalAs(UnmanagedType.AnsiBStr)] string msg);
        [MethodImplAttribute(MethodImplOptions.PreserveSig)]
        int Add(int a, int b);
    }
    
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        [DllImport("testintfdll.dll", EntryPoint = "GetImpl",CharSet = CharSet.Ansi, CallingConvention = CallingConvention.StdCall)]
        private static extern void GetImpl([MarshalAs(UnmanagedType.Interface)] out ITest instance);

        private void button1_Click(object sender, EventArgs e)
        {
            ITest tester;
            GetImpl(out tester);
            tester.ShowMessage(textBox1.Text);
            this.Text = tester.Add(100, 50).ToString();
        }
    }
}