应用程序在C＃中调用来自c ++的DLL的回调时退出

Question

我有这个类用c ++访问DLL我觉得我没有访问权限。只是一个简单的文档：

class SB6
{
        [UnmanagedFunctionPointer(CallingConvention.ThisCall)]
        public delegate void USBMESSAGEFUNCTION(byte Cmd, IntPtr pData, int DataLen);
        public static USBMESSAGEFUNCTION funct;
        [DllImport("USBENGINE.DLL")]
        extern public static bool InitialEngine();
        [DllImport("USBENGINE.DLL")]
        extern public static eUSB_Open StartUsbEngine();
        [DllImport("USBENGINE.DLL", CallingConvention = CallingConvention.Cdecl)]
        unsafe extern public static void SetMessageCallbackFunction(USBMESSAGEFUNCTION pFunc);
        [DllImport("USBENGINE.DLL")]
        extern public static void StopUsbEngine();
        [DllImport("USBENGINE.DLL")]
        extern public static void UnInitialEngine();
}


    public enum eUSB_Open
    {
        eOpen_Success = 0x00,//Successfully opened
        eOpen_Opened,//Already in open state 
        eOpen_No_Device,//No USB device
        eOpen_Open_Failed,//Open failed
        eOpen_No_Initial,//Dynamic library not initialized

    };

    public enum eUsbMsg
    {
        USB_MSG_CONNECT = 0x00,//USBEngien connected to currency-counting machine
        USB_MSG_DISCONNECT,//USBEngine disconnected from currency-counting machine
        USB_MSG_START,//Currency counting started (motor started)
        USB_MSG_DATA,//Currency-counting machine uploading currency information data
        USB_MSG_END,//Currency counting completed (motor stopped)
    };

    public struct SN_Data_Struct
    {
        public UInt16 Date;
        public UInt16 Time;
        public UInt16 tfFlag;
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 3)]
        public UInt16[] ErrorCode;
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 4)]
        public UInt16[] MoneyFlag;
        public UInt16 Ver;
        public UInt16 Value;
        public UInt16 CharNum;
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 12)]
        public UInt16[] SNo;
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 24)]
        public UInt16[] MachineSNo;
        public TImageSNo ImageSNo;
    };

    public struct TImageSNo
    {
        public UInt16 col;
        public UInt16 row;
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 2176+18+256)]
        public UInt16[] data;
    };

我在主表单上有这个代码：

public Form1()
    {
        InitializeComponent();
        bool status = SB6.InitialEngine();
    }

    static void onMessage(byte Cmd, IntPtr pData, int DataLen)
    {
        String cmd = Cmd.ToString();
        String serial = "";
        String response = "";
        String currency = "";
        byte[] res = new byte[DataLen];

        if (cmd == "0")
            response = eUsbMsg.USB_MSG_CONNECT.ToString();
        else if (cmd == "1")
            response = eUsbMsg.USB_MSG_DISCONNECT.ToString();
        else if (cmd == "2")
            response = eUsbMsg.USB_MSG_START.ToString();
        else if (cmd == "3")
        {
            response = eUsbMsg.USB_MSG_DATA.ToString();
            SN_Data_Struct output = (SN_Data_Struct)Marshal.PtrToStructure(pData, typeof(SN_Data_Struct));
            for (int x = 0; x < output.MoneyFlag.Length - 1; x++)
            {
                currency += (char)output.MoneyFlag[x];
            }
            for (int x = 0; x < output.SNo.Length; x++)
            {
                serial += (char)output.SNo[x];
            }
        }
        else if (cmd == "4")
            response = eUsbMsg.USB_MSG_END.ToString();
    }

    private void btnConnect_Click(object sender, EventArgs e)
    {
        eUSB_Open result = SB6.StartUsbEngine();

        if (result.ToString() == "eOpen_Success")
        {
            SB6.funct = new SB6.USBMESSAGEFUNCTION(onMessage);
            GC.KeepAlive(SB6.funct);
            SB6.SetMessageCallbackFunction(SB6.funct);
            MessageBox.Show("Successfully opened");
        }
        else
            MessageBox.Show("Failed to open");
    }
}

我的问题是，当SetMessageCallbackFunction被触发时，我的主表单中的onMessage函数会执行。但执行onMessage后，应用程序自行退出。我没有像application.exit这样的代码来退出应用程序或其他任何内容。

程序退出的原因可能是什么？请帮帮我。