BacgroundWorkerCompleted 不执行

Question

使用 C# .NET 4.0

我尝试使用 BackgroundWorker 来检索远程计算机上的服务列表。它作为后台工作程序运行，因此 UI 在等待信息时保持响应。

我的做法是，将对信息的请求放在后台worker的_DoWork方法中，并使用ManualResetEvent.Set()来指示信息已被处理。应在 _RunWorkerCompleted 方法中设置 ManaualResetEvent。 _RunWorkerCompleted 永远不会执行。

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

这是因为 RunWorkerCompleted 事件在 UI 线程上触发，您通过对 WaitOne 的 ManualResetEvent 调用在按钮单击处理程序中阻止了该事件。

为什么不在 RunWorkerCompleted 事件处理程序中更新 GUI，而不是使用 ManualResetEvent？