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 = 0;
            long sum = 0;

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

            for (int i=0;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(10);//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 / 10, "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(1000);//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.");
            }
        }
    }
}