Question

Using C# .NET 4.0

I am trying to use a BackgroundWorker to retrieve a list of the services on a remote computer. This is run as a background worker so the UI remains responsive while waiting for the information.

My approach is to place the request for information in the _DoWork method of the background worker, and use ManualResetEvent.Set() to indicate that the information has been processed. The ManaualResetEvent should be set in the _RunWorkerCompleted method. _RunWorkerCompleted never executes.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Windows.Forms;
using System.ServiceProcess;
using System.Threading;
using System.Diagnostics;

namespace DemoTest
{

    public partial class Form1 : Form
    {
        List<ServiceController> MyBox1Services;

        ManualResetEvent MyBox1ServicesObtained = new ManualResetEvent(false);


        public Form1()
        {
            InitializeComponent();

        }



        private void button1_Click(object sender, EventArgs e)
        {

            // Use background worker to get the list of services in the background
            BackgroundWorker MyBox1Servicess = new BackgroundWorker();
            MyBox1Servicess.DoWork += new DoWorkEventHandler(bwGetMyBox1Services_DoWork);
            MyBox1Servicess.RunWorkerCompleted += new RunWorkerCompletedEventHandler(MyBox1Servicess_RunWorkerCompleted);




            MyBox1Servicess.RunWorkerAsync();

            // Wait until all the services have been obtained before moving on

            MyBox1ServicesObtained.Reset();

            MyBox1ServicesObtained.WaitOne();


            // Update the GUI Here....


        }


        void MyBox1Servicess_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            if ((e.Cancelled == true))
            {
                MessageBox.Show("Canceled!");
            }

            else if (!(e.Error == null))
            {
                MessageBox.Show(e.Error.Message);
            }

            else
            {
                Debug.WriteLine("MyBox1Servicess_RunWorkerCompleted");
            }
            MyBox1Services = (List<ServiceController>)e.Result;
            MyBox1ServicesObtained.Set();
        }


        void bwGetMyBox1Services_DoWork(object sender, DoWorkEventArgs e)
        {
            BackgroundWorker worker = sender as BackgroundWorker;
            ServiceController[] allServices;
            List<ServiceController> allServicesList = new List<ServiceController>();

            try
            {
                allServices = ServiceController.GetServices("MyBox1");
                foreach (ServiceController sc in allServices)
                {
                    allServicesList.Add(sc);
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString());
            }
            e.Result = allServicesList;
        }

    }
}

Answer 1

This is because the RunWorkerCompleted event is firing on the UI thread, which you blocked in the button click handler with the ManualResetEvent call to WaitOne.’

Rather than use the ManualResetEvent, why not just update your GUI in the RunWorkerCompleted event handler?