IM SDK API 

/// 

    /// IM SDK 初始化。
    /// 
    /// 
    /// 
    /// 
    [DllImport(@"imsdk.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Ansi)]
    public extern static int TIMInit(long sdk_app_id, string json_sdk_config);

/// 

    /// 登录
    /// 
    /// 用户id
    /// 签名
    /// 
    /// 
    [DllImport(@"imsdk.dll", CallingConvention = CallingConvention.Cdecl)]
    private extern static int TIMLogin(string user_id, string user_sig, TIMCommCallback cb);

/// 

    /// 接收新消息回调
    /// 
    /// 
    [DllImport(@"imsdk.dll", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Ansi)]
    private extern static void TIMAddRecvNewMsgCallback(delegateTIMRecvNewMsgCallback cb);

public void ImInit()
    {
      int sdk_app_id = 1400000000;
      var data = new { sdk_config_log_file_path = AppDomain.CurrentDomain.BaseDirectory, sdk_config_config_file_path = AppDomain.CurrentDomain.BaseDirectory };
      TIMInit(sdk_app_id, JsonConvert.SerializeObject(data));
      TIMAddRecvNewMsgCallback(TIMRecvNewMsgCallback);
      var tLSSig = new TLSSigAPIv2(sdk_app_id, "163250645178b565ffc0b22618d14a88d8a91d86f0e76813313197a5xxxxxxx");
      TIMLogin("用户", tLSSig.GenSig("用户"), CommCallback);

    }
    private delegate int TIMCommCallback(int code, string desc, string json_params);
    
    private int CommCallback(int code, string desc, string json_params)
    {
      return code;
    }
    public delegate void delegateTIMRecvNewMsgCallback([MarshalAs(UnmanagedType.CustomMarshaler, MarshalTypeRef = typeof(Utf8Marshaler))] string json_msg_array, IntPtr user_data);;
    private void TIMRecvNewMsgCallback(string json_msg_array, IntPtr user_data) {
      var b = Encoding.Default.GetBytes(json_msg_array);
      richTextBox1.AppendText(Encoding.UTF8.GetString(b));
    }

    private void Form1_Load(object sender, EventArgs e)
    {
     ImInit();
    }

public class Utf8Marshaler : ICustomMarshaler
    {
        public void CleanUpManagedData(object managedObj)
        {
        }
 
        public void CleanUpNativeData(IntPtr pNativeData)
        {
            Marshal.FreeHGlobal(pNativeData);
        }
 
        public int GetNativeDataSize()
        {
            return -1;
        }
 
        public IntPtr MarshalManagedToNative(object managedObj)
        {
            if (object.ReferenceEquals(managedObj, null))
                return IntPtr.Zero;
            if (!(managedObj is string))
                throw new InvalidOperationException();
 
            byte[] utf8Bytes = Encoding.UTF8.GetBytes((string)managedObj);
            IntPtr ptr = Marshal.AllocHGlobal(utf8Bytes.Length + 1);
            Marshal.Copy(utf8Bytes, 0, ptr, utf8Bytes.Length);
            Marshal.WriteByte(ptr, utf8Bytes.Length, 0);
            return ptr;
        }
 
        public object MarshalNativeToManaged(IntPtr pNativeData)
        {
            if (pNativeData == IntPtr.Zero)
                return null;
 
            List bytes = new List();
            for (int offset = 0; ; offset++)
            {
                byte b = Marshal.ReadByte(pNativeData, offset);
                if (b == 0)
                    break;
                else
                    bytes.Add(b);
            }
            return Encoding.UTF8.GetString(bytes.ToArray(), 0, bytes.Count);
        }
 
        private static readonly Utf8Marshaler Instance = new Utf8Marshaler();
        public static ICustomMarshaler GetInstance(string cookie)
        {
            return Instance;
        }
    }