Connecting to Digital Scale(Metler Toledo PS90) as HID runs OnReport only when cable is connected to computer for first time

问题

I am using Mike O Brien's HID Library to connect to digital scale, Device opens successfully then displays device attached & removed messages perfectly. But only runs OnReport for about 20 times initially
After Inital approx 20 runs on OnReport it never runs again, unless I remove usb cable and re-connect.

My code is below

if (scale.IsConnected)
      {
          scale.Inserted += DeviceAttachedHandler;
          scale.Removed += DeviceRemovedHandler;
          scale.MonitorDeviceEvents = true;
          scale.ReadReport(OnReport);
MessageBox.Show("Hold Application Here");

Event Handlers for the scale

private void DeviceAttachedHandler()
    {
        MessageBox.Show("Device attached.");
        scale.ReadReport(OnReport);
    }

    private static void DeviceRemovedHandler()
    {
        MessageBox.Show("Device removed.");
    }
    private void OnReport(HidReport report)
    {
        if (!scale.IsConnected) { return; }


        //var cardData = new Data(report.Data);
        decimal weight = Convert.ToDecimal(report.Data[4]);// (Convert.ToDecimal(report.Data[4]) +



        MessageBox.Show(weight.ToString());
//Convert.ToDecimal(report.Data[5]) * 256) / 100;
            //Console.WriteLine(!cardData.Error ? Encoding.ASCII.GetString(cardData.CardData) : cardData.ErrorMessage);
            //Console.WriteLine(report.Data);
        scale.ReadReport(OnReport);
    }

回答1:

I managed to get the scale working, In my callback which runs when scale returns data I was doing Read which is a blocking call. So a deadlock was created, should have only used ReadReport or Read take a look at Mike's example below which he posted here .

using System;
using System.Linq;
using System.Text;
using HidLibrary;

namespace MagtekCardReader
{
    class Program
    {
        private const int VendorId = 0x0801;
        private const int ProductId = 0x0002;

        private static HidDevice _device;

        static void Main()
        {
            _device = HidDevices.Enumerate(VendorId, ProductId).FirstOrDefault();

            if (_device != null)
            {
                _device.OpenDevice();

                _device.Inserted += DeviceAttachedHandler;
                _device.Removed += DeviceRemovedHandler;

                _device.MonitorDeviceEvents = true;

                _device.ReadReport(OnReport);

                Console.WriteLine("Reader found, press any key to exit.");
                Console.ReadKey();

                _device.CloseDevice();
            }
            else
            {
                Console.WriteLine("Could not find reader.");
                Console.ReadKey();
            }
        }

        private static void OnReport(HidReport report)
        {
            if (!_device.IsConnected) { return; }

            var cardData = new Data(report.Data);

            Console.WriteLine(!cardData.Error ? Encoding.ASCII.GetString(cardData.CardData) : cardData.ErrorMessage);

            _device.ReadReport(OnReport);
        }

        private static void DeviceAttachedHandler()
        {
            Console.WriteLine("Device attached.");
            _device.ReadReport(OnReport);
        }

        private static void DeviceRemovedHandler()
        {
            Console.WriteLine("Device removed.");
        }
    }
}

来源：https://stackoverflow.com/questions/10130837/connecting-to-digital-scalemetler-toledo-ps90-as-hid-runs-onreport-only-when-c