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BackgroundWorker 在執(zhí)行DoWork事件時(shí)該如何取消呢?

方法1 DoWork 執(zhí)行一個(gè)(耗時(shí))循環(huán)

方法2 DoWork執(zhí)行一個(gè)(耗時(shí))方法[注:方法沒(méi)有循環(huán)]

見(jiàn)代碼:

方法1中DoWork事件執(zhí)行的是一個(gè)for循環(huán)(foreach,while.....)

取消操作很簡(jiǎn)單,只要在循環(huán)中判斷即可

看代碼---------代碼是從網(wǎng)上拷貝下來(lái)的,這種例子網(wǎng)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,但還未取消

          else { break; }

        }

      }

      //Console.ReadLine();

    }

    static void bw_DoWork(object sender, DoWorkEventArgs e)

    {

      Console.WriteLine(e.Argument);

      for (int i = 0; i <= 100; i += 1)

      {

        //判斷是否取消操作

        if (bw.CancellationPending)

        {

          e.Cancel = true; //這里才真正取消

          return;

        }

        //傳遞給ProgressChanged

        bw.ReportProgress(i);

        Thread.Sleep(100);

        e.Result = i;

      }

      // 最終傳遞給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);      // 從 DoWork 傳過(guò)來(lái)的參數(shù)

      }

    }

    static void bw_ProgressChanged(object sender, ProgressChangedEventArgs e)

    {

      Console.Write("{0,3}/b/b/b", e.ProgressPercentage);

    }

  }

}

#endregion

如果方法2中DoWork事件中執(zhí)行的是一個(gè)比較耗時(shí)的方法時(shí)該怎么辦了？方法中沒(méi)有循環(huán)無(wú)法判斷用戶(hù)是否執(zhí)行了取消操作！

那么這里就要用到[異步編程模式]，在執(zhí)行一個(gè)比較耗時(shí)的方法時(shí)，代碼還能繼續(xù)向下運(yùn)行.....！

請(qǐng)看下面代碼：

BackgroundWorker bgworker = new BackgroundWorker(); 

gworker.WorkerSupportsCancellation = true; //是否支持異步取消  如果要取消操作必須設(shè)置true 

bgworker.DoWork += new DoWorkEventHandler(this.bgworker_DoWork); 

bgworker.RunWorkerCompleted += new RunWorkerCompletedEventHandler(this.bgworker_RunWorkerCompleted); 

   private void begin_Click(object sender, EventArgs e) 

   { 

     //開(kāi)始 

      if(!bgworker.IsBusy) 

       { 

           bgworker.RunWorkerAsync(); //開(kāi)始操作 

        } 

   } 

   private void end_Click(object sender, EventArgs e) 

   { 

     //開(kāi)始取消 

     if (bgworker.IsBusy) //是否在運(yùn)行異步操作 

     { 

       bgworker.CancelAsync(); //(是)提交取消命令 

     } 

   } 

   private void bgworker_DoWork(object sender, DoWorkEventArgs e) 

   { 

     //Sql語(yǔ)句 查詢(xún)的數(shù)據(jù)很多 

     string sql = "select * from table";   

     //綁定委托要執(zhí)行的方法 

     Del_DoWork work = new Del_DoWork(ReturnDataTable); //可以使用：delegate、Action、Func、predicate 等，具體可參考：C#委托的介紹(delegate、Action、Func、predicate) 和 委托的N種寫(xiě)法

     //開(kāi)始異步執(zhí)行(ReturnDataTable)方法 

     IAsyncResult ret = work.BeginInvoke(sql, null, null);  

     //(異步編程模式好久就是在執(zhí)行一個(gè)很耗時(shí)的方法(ReturnDataTable)時(shí),還能向下繼續(xù)運(yùn)行代碼) 

     //接著運(yùn)行下面的while循環(huán), 

     //判斷異步操作是否完成 

     while (!ret.IsCompleted)   

     { 

       //沒(méi)完成 

       //判斷是否取消了backgroundworker異步操作 

       if (bgworker.CancellationPending)  

       { 

         //如何是  馬上取消backgroundwork操作(這個(gè)地方才是真正取消) 

         e.Cancel = true;  

         return; 

       } 

     } 

     e.Result = work.EndInvoke(ret); //返回查詢(xún)結(jié)果 賦值給e.Result 

   } 

   private delegate DataTable Del_DoWork(string sql);  //創(chuàng)建一個(gè)委托 

   /// 
 

   /// 查詢(xún)數(shù)據(jù)庫(kù)表--------一個(gè)很耗時(shí)的方法 

   ///  

   ///  

   ///  

   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("出現(xiàn)錯(cuò)誤!"); 

     } 

     else 

     { 

       DataTable table = e.Result as DataTable; 

       if (table != null) 

       { 

         //得到數(shù)據(jù),進(jìn)行顯示操作 

         //dataGridView1.DataSource = table; 

       } 

     } 

   } 

我這里主要是用方法2，在很多情況下，我們的DoWork事件都是執(zhí)行一個(gè)方法，而不是一個(gè)循環(huán)....，如果你也遇到要執(zhí)行一個(gè)耗時(shí)方法，又要取消操作的話(huà)，請(qǐng)用方法2吧！