c# - USB 中继 DLL 问题 - 继续

Question

此下有一个关于此的问题USB relay DLL problems [closed] 。 cubrr 给出了一个很好的可接受的答案。 。但是当我尝试编译该程序时，有一段代码给了我一个错误。错误说

Attribute 'MarshalAs' is not valid on this declaration type. It is only valid on 'field, param, return' declarations

这是cubrr's代码

using System;
using System.Runtime.InteropServices;

namespace UsbRelay
{
    public static class UsbRelayDevice
    {
        /// <summary>
        /// Init the USB Relay Libary
        /// </summary>
        /// <returns>This function returns 0 on success and -1 on error.</returns>
        [DllImport("usb_relay_device.dll", EntryPoint = "usb_relay_init")]
        public static extern int Init();

        /// <summary>
        /// Finalize the USB Relay Libary.
        /// This function frees all of the static data associated with
        /// USB Relay Libary. It should be called at the end of execution to avoid
        /// memory leaks.
        /// </summary>
        /// <returns>This function returns 0 on success and -1 on error.</returns>
        [DllImport("usb_relay_device.dll", EntryPoint = "usb_relay_exit")]
        public static extern int Exit();

        /// <summary>
        /// Enumerate the USB Relay Devices.
        /// </summary>
        /// <returns></returns>
        [DllImport("usb_relay_device.dll", EntryPoint = "usb_relay_device_enumerate")]
        public static extern UsbRelayDeviceInfo Enumerate();

        /// <summary>
        /// Free an enumeration Linked List
        /// </summary>
        /// <param name="deviceInfo"></param>
        [DllImport("usb_relay_device.dll", EntryPoint = "usb_relay_device_free_enumerate")]
        public static extern void FreeEnumerate(UsbRelayDeviceInfo deviceInfo);

        /// <summary>
        /// Open device that serial number is serialNumber
        /// </summary>
        /// <param name="serialNumber"></param>
        /// <param name="stringLength"></param>
        /// <returns>This funcation returns a valid handle to the device on success or NULL on failure.</returns>
        [DllImport("usb_relay_device.dll", EntryPoint = "usb_relay_device_open_with_serial_number", CharSet = CharSet.Ansi)]
        public static extern int OpenWithSerialNumber([MarshalAs(UnmanagedType.LPStr)] string serialNumber, int stringLength);

        /// <summary>
        /// Open a usb relay device
        /// </summary>
        /// <param name="deviceInfo"></param>
        /// <returns>This funcation returns a valid handle to the device on success or NULL on failure.</returns>
        [DllImport("usb_relay_device.dll", EntryPoint = "usb_relay_device_open")]
        public static extern int Open(UsbRelayDeviceInfo deviceInfo);

        /// <summary>
        /// Close a usb relay device
        /// </summary>
        /// <param name="hHandle"></param>
        [DllImport("usb_relay_device.dll", EntryPoint = "usb_relay_device_close")]
        public static extern void Close(int hHandle);

        /// <summary>
        /// open a relay channel on the USB-Relay-Device
        /// </summary>
        /// <param name="hHandle">Which usb relay device your want to operate</param>
        /// <param name="index">Which channel your want to open</param>
        /// <returns>0 -- success; 1 -- error; 2 -- index is outnumber the number of the usb relay device</returns>
        [DllImport("usb_relay_device.dll", EntryPoint = "usb_relay_device_open_one_relay_channel")]
        public static extern int OpenOneRelayChannel(int hHandle, int index);

        /// <summary>
        /// open all relay channel on the USB-Relay-Device
        /// </summary>
        /// <param name="hHandle">which usb relay device your want to operate</param>
        /// <returns>0 -- success; 1 -- error</returns>
        [DllImport("usb_relay_device.dll", EntryPoint = "usb_relay_device_open_all_relay_channel")]
        public static extern int OpenAllRelayChannels(int hHandle);

        /// <summary>
        /// close a relay channel on the USB-Relay-Device
        /// </summary>
        /// <param name="hHandle">which usb relay device your want to operate</param>
        /// <param name="index">which channel your want to close</param>
        /// <returns>0 -- success; 1 -- error; 2 -- index is outnumber the number of the usb relay device</returns>
        [DllImport("usb_relay_device.dll", EntryPoint = "usb_relay_device_close_one_relay_channel")]
        public static extern int CloseOneRelayChannel(int hHandle, int index);

        /// <summary>
        /// close all relay channel on the USB-Relay-Device
        /// </summary>
        /// <param name="hHandle">hich usb relay device your want to operate</param>
        /// <returns>0 -- success; 1 -- error</returns>
        [DllImport("usb_relay_device.dll", EntryPoint = "usb_relay_device_close_all_relay_channel")]
        public static extern int CloseAllRelayChannels(int hHandle);

        /// <summary>
        /// status bit: High --> Low 0000 0000 0000 0000 0000 0000 0000 0000, one bit indicate a relay status.
        /// the lowest bit 0 indicate relay one status, 1 -- means open status, 0 -- means closed status.
        /// bit 0/1/2/3/4/5/6/7/8 indicate relay 1/2/3/4/5/6/7/8 status
        /// </summary>
        /// <param name="hHandle"></param>
        /// <param name="status"></param>
        /// <returns>0 -- success; 1 -- error</returns>
        [DllImport("usb_relay_device.dll", EntryPoint = "usb_relay_device_get_status")]
        public static extern int GetStatus(int hHandle, ref int status);
    }

    /// <summary>
    /// USB relay board info structure
    /// </summary>
    [StructLayout(LayoutKind.Sequential, Pack=8)]
    public class UsbRelayDeviceInfo
    {
        [MarshalAs(UnmanagedType.LPStr)] //Error is here
        public string SerialNumber { get; set; }

        [MarshalAs(UnmanagedType.LPStr)] //Error is here
        public string DevicePath { get; set; }

        public UsbRelayDeviceType Type { get; set; }

        public UsbRelayDeviceInfo Next { get; set; }
    }

    public enum UsbRelayDeviceType
    {
        OneChannel = 1,
        TwoChannel = 2,
        FourChannel = 4,
        EightChannel = 8
    }
}

这里有错误

/// <summary>
        /// USB relay board info structure
        /// </summary>
        [StructLayout(LayoutKind.Sequential, Pack=8)]
        public class UsbRelayDeviceInfo
        {
            [MarshalAs(UnmanagedType.LPStr)] //Error is here
            public string SerialNumber { get; set; }

            [MarshalAs(UnmanagedType.LPStr)] //Error is here
            public string DevicePath { get; set; }

            public UsbRelayDeviceType Type { get; set; }

            public UsbRelayDeviceInfo Next { get; set; }
        }

请帮我解决这个问题

Here is the Hardware part details

Here is the SDK that provide by hardware vender

Answer 1

错误消息告诉您确切的问题。

属性，甚至自动属性，都无法编码。只有普通的旧字段。

改变

public string SerialNumber { get; set; }
 //                        ^^^^^^^^^^^^^^
 //                        REMOVE THIS

至

public string SerialNumber;