C# 如何取消BackgroundWorker异步操作

BackgroundWorker 在执行DoWork事件时该如何取消呢?

 

方法1 DoWork 执行一个(耗时)循环

 

方法2 DoWork执行一个(耗时)方法[注:方法没有循环]

 

见代码:

方法1中DoWork事件执行的是一个for循环(foreach,while.....) 

 

取消操作很简单,只要在循环中判断即可

 

看代码---------代码是从网上拷贝下来的,这种例子网上很多

 

#region
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.ComponentModel;
using System.Threading;
using System.Text.RegularExpressions;

namespace ConsoleBackgroundworker
{
  class Program
  {
    static BackgroundWorker bw;
    static void Main()
    {
      bw = new BackgroundWorker();
      bw.WorkerReportsProgress = true;
      bw.WorkerSupportsCancellation = true;
      bw.DoWork += bw_DoWork;
      bw.ProgressChanged += bw_ProgressChanged;
      bw.RunWorkerCompleted += bw_RunWorkerCompleted;
      bw.RunWorkerAsync("Hello to worker");
      Console.WriteLine("Press /"C/" to cancel");

      while (true)
      {
        //按C取消
        if (Console.ReadKey(true).Key == ConsoleKey.C)
        {
          if (bw.IsBusy)
            bw.CancelAsync(); //提交取消命令,但还未取消
          else { break; }
        }
      }
      //Console.ReadLine();
    }

    static void bw_DoWork(object sender, DoWorkEventArgs e)
    {
      Console.WriteLine(e.Argument);
      for (int i = 0; i <= 100; i += 1)
      {
        //判断是否取消操作
        if (bw.CancellationPending)
        {
          e.Cancel = true; //这里才真正取消
          return;
        }
        //传递给ProgressChanged
        bw.ReportProgress(i);
        Thread.Sleep(100);
        e.Result = i;
      }
      // 最终传递给RunWorkerCopmleted
    }

    static void bw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
    {
      if (e.Cancelled)
        Console.WriteLine("You cancelled!");
      else if (e.Error != null)
        Console.WriteLine("Worker exception: " + e.Error.ToString());
      else
      {
        Console.WriteLine("Complete - " + e.Result);      // 从 DoWork
      }
    }

    static void bw_ProgressChanged(object sender, ProgressChangedEventArgs e)
    {
      Console.Write("{0,3}/b/b/b", e.ProgressPercentage);
    }
  }
}
#endregion

 

方法2中DoWork事件中执行的是一个比较耗时的方法时该怎么办了.方法中没有循环无法判断用户是否执行了取消操作!

 

那么这里就要用到[异步编程模式],在执行一个比较耗时的方法时,代码还能继续向下运行.....!

 

请看下面代码-----------此代码是本人自己写的

BackgroundWorker bgworker = new BackgroundWorker();
gworker.WorkerSupportsCancellation = true; //是否支持异步取消  如果要取消操作必须设置true
     bgworker.DoWork += new DoWorkEventHandler(this.bgworker_DoWork);
     bgworker.RunWorkerCompleted += new RunWorkerCompletedEventHandler(this.bgworker_RunWorkerCompleted);

   private void begin_Click(object sender, EventArgs e)
   {
     //开始
      if(!bgworker.IsBusy)
       {
           bgworker.RunWorkerAsync(); //开始操作
        }
   }

   private void end_Click(object sender, EventArgs e)
   {
     //开始取消
     if (bgworker.IsBusy) //是否在运行异步操作
     {
       bgworker.CancelAsync(); //(是)提交取消命令
     }
   }

   private void bgworker_DoWork(object sender, DoWorkEventArgs e)
   {
     //Sql语句 查询的数据很多
     string sql = "select * from table";

     //绑定委托要执行的方法
     Del_DoWork work = new Del_DoWork(ReturnDataTable);

     //开始异步执行(ReturnDataTable)方法
     IAsyncResult ret = work.BeginInvoke(sql, null, null);

     //(异步编程模式好久就是在执行一个很耗时的方法(ReturnDataTable)时,还能向下继续运行代码)

     //接着运行下面的while循环,
     //判断异步操作是否完成
     while (!ret.IsCompleted)
     {
       //没完成
       //判断是否取消了backgroundworker异步操作
       if (bgworker.CancellationPending)
       {
         //如何是  马上取消backgroundwork操作(这个地方才是真正取消)
         e.Cancel = true;
         return;
       }
     }
     e.Result = work.EndInvoke(ret); //返回查询结果 赋值给e.Result
   }

   private delegate DataTable Del_DoWork(string sql);  //创建一个委托
   /// <summary>
   /// 查询数据库表--------一个很耗时的方法
   /// </summary>
   /// <param name="sql"></param>
   /// <returns></returns>
   private DataTable ReturnDataTable(string sql)
   {
     DataTable table = new DataTable();
     SqlConnection conn = new SqlConnection("Server............");
     //.....................(省略)
     return table;
   }

   private void bgworker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
   {
     if (e.Cancelled)
     {
       MessageBox.Show("您取消了操作!");
     }
     else if (e.Error != null)
     {
       MessageBox.Show("出现错误!");
     }
     else
     {
       DataTable table = e.Result as DataTable;
       if (table != null)
       {
         //得到数据,进行显示操作
         //dataGridView1.DataSource = table;
       }
     }
   }

 

 

我这里主要是方法2，在很多情况下,我们的DoWork事件都是执行一个方法,而不是一个循环....如果你也遇到要执行一个耗时方法,又要取消操作的话,请用方法2吧!

http://blog.csdn.net/wxm3630478/article/details/6126459