C# BackgroundWorker（异步线程）

日期：2018年11月28日

环境：Windows 10，VS2015

前言

.NET 类库中提供了一个快捷使用多线程的帮助类BackgroundWorker，能够快速创建一个新的线程，并能报告进度，暂停，以及在线程完成后处理别的任务。

创建简单UI

Demo code

  1 using System;
  2 using System.Collections.Generic;
  3 using System.ComponentModel;
  4 using System.Data;
  5 using System.Drawing;
  6 using System.Linq;
  7 using System.Text;
  8 using System.Threading;
  9 using System.Threading.Tasks;
 10 using System.Windows.Forms;
 11 
 12 namespace BackgroundWorkerTest
 13 {
 14     public partial class Form1 : Form
 15     {
 16         private BackgroundWorker bkgdWorker;
 17         public Form1()
 18         {
 19             InitializeComponent();
 20         }
 21 
 22         private void Form1_Load(object sender, EventArgs e)
 23         {
 24             bkgdWorker = new BackgroundWorker();
 25             bkgdWorker.WorkerReportsProgress = true;//允许报告进度
 26             bkgdWorker.WorkerSupportsCancellation = true;//允许取消线程
 27             bkgdWorker.DoWork += new DoWorkEventHandler(bkgdWorker_DoWork);//添加主要工作
 28             bkgdWorker.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bkgdWorker_RunWorkerCompleted);//添加线程完成的处理
 29             bkgdWorker.ProgressChanged += new ProgressChangedEventHandler(bkgdWorker_ProgressChanged);//添加进度变化处理
 30         }
 31 
 32         //主要工作逻辑（不可处理UI相关）
 33         private void bkgdWorker_DoWork(Object sender, DoWorkEventArgs e)
 34         {
 35             BackgroundWorker bw = (BackgroundWorker)sender;
 36             int n = 0;
 37             long sum = 0;
 38 
 39             if (e.Argument != null)
 40             {
 41                 n = (int)e.Argument;
 42             }
 43 
 44             for (int i=0;i<= n; i++)
 45             {
 46                 if (bw.CancellationPending)
 47                 {
 48                     e.Cancel = true;//此处设置Cancel=true后，就可以在RunWorkerCompleted中判断e.Cancelled是否为true
 49                     break;
 50                 }
 51                 sum += i;
 52                 Thread.Sleep(10);//避免太快，让线程暂停一会再报告进度
 53                 //bw.ReportProgress(i/10);//报告进度//调用ReportProgress()方法报告进度，同时触发ProgressChanged事件
 54                 bw.ReportProgress(i / 10, "当前i的值为"+ Convert.ToString(i));//报告进度和userState
 55             }
 56             e.Result = sum;
 57         }
 58 
 59         //进度变化处理
 60         private void bkgdWorker_ProgressChanged(Object sender, ProgressChangedEventArgs e)
 61         {
 62             pbr_Test.Value = e.ProgressPercentage;
 63             lb_Message.Text = e.UserState.ToString();
 64         }
 65 
 66         //线程完成处理
 67         private void bkgdWorker_RunWorkerCompleted(Object sender, RunWorkerCompletedEventArgs e)
 68         {
 69             if (!(e.Error == null))
 70             {
 71                 MessageBox.Show("Fail:"+e.Error.Message);
 72             }
 73             else if(e.Cancelled)
 74             {
 75                 MessageBox.Show("Failed: thread Cancelled by operator");
 76             }
 77             else
 78             {
 79                 lb_Message.Text = "计算结果为：" + e.Result.ToString();
 80                 MessageBox.Show("thread complete");
 81             }
 82         }
 83 
 84         private void btn_Start_Click(object sender, EventArgs e)
 85         {
 86             if (bkgdWorker.IsBusy)
 87                 MessageBox.Show("The thead running now.");
 88             else
 89                 bkgdWorker.RunWorkerAsync(1000);//调用该方法才会启动线程
 90         }
 91 
 92         private void btn_Cancal_Click(object sender, EventArgs e)
 93         {
 94             if (bkgdWorker.IsBusy)
 95             {
 96                 bkgdWorker.CancelAsync();//取消线程
 97             }
 98             else
 99             {
100                 MessageBox.Show("There is no thead running now.");
101             }
102         }
103     }
104 }