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

 using System;
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Data;
 using System.Drawing;
 using System.Linq;
 using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
 using System.Windows.Forms;

 namespace BackgroundWorkerTest
 {
     public partial class Form1 : Form
     {
         private BackgroundWorker bkgdWorker;
         public Form1()
         {
             InitializeComponent();
         }

         private void Form1_Load(object sender, EventArgs e)
         {
             bkgdWorker = new BackgroundWorker();
             bkgdWorker.WorkerReportsProgress = true;//允许报告进度
             bkgdWorker.WorkerSupportsCancellation = true;//允许取消线程
             bkgdWorker.DoWork += new DoWorkEventHandler(bkgdWorker_DoWork);//添加主要工作
             bkgdWorker.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bkgdWorker_RunWorkerCompleted);//添加线程完成的处理
             bkgdWorker.ProgressChanged += new ProgressChangedEventHandler(bkgdWorker_ProgressChanged);//添加进度变化处理
         }

         //主要工作逻辑（不可处理UI相关）
         private void bkgdWorker_DoWork(Object sender, DoWorkEventArgs e)
         {
             BackgroundWorker bw = (BackgroundWorker)sender;
             int n = ;
             long sum = ;

             if (e.Argument != null)
             {
                 n = (int)e.Argument;
             }

             for (int i=;i<= n; i++)
             {
                 if (bw.CancellationPending)
                 {
                     e.Cancel = true;//此处设置Cancel=true后，就可以在RunWorkerCompleted中判断e.Cancelled是否为true
                     break;
                 }
                 sum += i;
                 Thread.Sleep();//避免太快，让线程暂停一会再报告进度
                 //bw.ReportProgress(i/10);//报告进度//调用ReportProgress()方法报告进度，同时触发ProgressChanged事件
                 bw.ReportProgress(i / , "当前i的值为"+ Convert.ToString(i));//报告进度和userState
             }
             e.Result = sum;
         }

         //进度变化处理
         private void bkgdWorker_ProgressChanged(Object sender, ProgressChangedEventArgs e)
         {
             pbr_Test.Value = e.ProgressPercentage;
             lb_Message.Text = e.UserState.ToString();
         }

         //线程完成处理
         private void bkgdWorker_RunWorkerCompleted(Object sender, RunWorkerCompletedEventArgs e)
         {
             if (!(e.Error == null))
             {
                 MessageBox.Show("Fail:"+e.Error.Message);
             }
             else if(e.Cancelled)
             {
                 MessageBox.Show("Failed: thread Cancelled by operator");
             }
             else
             {
                 lb_Message.Text = "计算结果为：" + e.Result.ToString();
                 MessageBox.Show("thread complete");
             }
         }

         private void btn_Start_Click(object sender, EventArgs e)
         {
             if (bkgdWorker.IsBusy)
                 MessageBox.Show("The thead running now.");
             else
                 bkgdWorker.RunWorkerAsync();//调用该方法才会启动线程
         }

         private void btn_Cancal_Click(object sender, EventArgs e)
         {
             if (bkgdWorker.IsBusy)
             {
                 bkgdWorker.CancelAsync();//取消线程
             }
             else
             {
                 MessageBox.Show("There is no thead running now.");
             }
         }
     }
 }