使用前提

在WPF程序中，有一些比较耗时的后台操作时，比如向远程服务器请求数据，或者通过TCP/IP为某台设备提供升级固件服务等等。为了防止这类操作freeze用户界面，造成用户体验下降，即程序假死的状况出现。一种常见的，更user friendly的方式是，提供一个进度条窗口，提示用户该操作的完成进度。并提供取消操作的选项。
C#中的 BackgroundWorker Class .aspx)则是执行该任务的最佳选择。

The BackgroundWorker class allows you to run an operation on a separate, dedicated thread. Time-consuming operations like downloads and database transactions can cause your user interface (UI) to seem as though it has stopped responding while they are running. When you want a responsive UI and you are faced with long delays associated with such operations, theBackgroundWorker class provides a convenient solution. -MSDN

关于 BackgroundWorker 类

主要属性

  • CancellationPending - 只读属性，default值为false，执行CancelAsync方法后，值为true。表明应用程序请求了取消后台操作。
  • IsBusy - 如果后台异步操作开始执行，值为true，否则为false
  • WorkerReportProgress - 如果BackgroundWorker支持后台操作进程更新，设置值为true，default值为false

主要事件

  • DoWork
  • ProgressChanged
  • RunWorkerCompleted
    不要再DoWork事件处理程序中对UI线程中的对象进行操作，操作应该放在ProgressChanged和RunWorkerCompleted的事件处理程序中。

主要方法

  • RunWorkerAsync() - 执行后台操作，激发DoWork事件
  • ReportProgress()- 激发ProgressChanged事件
  • CancelAsync() - 提交终止后台操作的请求，并将CancellationPending属性值设为true。在程序其他地方要定时检查CancellationPending属性的值，作出相应操作，比如
  1. if (worker.CancellationPending)
  2. {
  3.     e.Cancel = true;
  4. }

示例程序

XAML

  1. <Window x:Class="BackgroundWorkerExample.MainWindow"  
  2.         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"  
  3.         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"  
  4.         Title="MainWindow" Height="150" Width="300">
  5.     <StackPanel>
  6.         <ProgressBar Name="progressBar" Height="20" Width="250" Margin="10"></ProgressBar>
  7.         <TextBox Name="textBox" Width="50" Height="20" HorizontalAlignment="Center"></TextBox>
  8.         <Button Name="btnProcess" Width="100" Click="btnProcess_Click" Margin="5">Start</Button>
  9.         <Button Name="btnCancel" Width="100" Click="btnCancel_Click" Margin="5">Cancel</Button>
  10.     </StackPanel>
  11. </Window>

C#

  1. namespace BackgroundWorkerExample
  2. {
  3.     /// <summary>
  4.     /// Interaction logic for MainWindow.xaml
  5.     /// </summary>
  6.     public partial class MainWindow : Window
  7.     {
  8.         BackgroundWorker bgworker = new BackgroundWorker();
  9.         public MainWindow()
  10.         {
  11.             InitializeComponent();
  12.             bgworker.WorkerReportsProgress = true;
  13.             bgworker.WorkerSupportsCancellation = true;
  14.             bgworker.DoWork += bgworker_DoWork;
  15.             bgworker.ProgressChanged += bgworker_ProgressChanged;
  16.             bgworker.RunWorkerCompleted += bgworker_RunWorkerCompleted;
  17.         }
  18.         void bgworker_DoWork(object sender, DoWorkEventArgs e)
  19.         {
  20.             BackgroundWorker worker = sender as BackgroundWorker;
  21.             for (int i = 1; i <= 100; i++)
  22.             {
  23.                 if (worker.CancellationPending)
  24.                 {
  25.                     e.Cancel = true;
  26.                 }
  27.                 else
  28.                 {
  29.                     worker.ReportProgress(i);
  30.                     Thread.Sleep(100);
  31.                 }
  32.             }
  33.         }
  35.         void bgworker_ProgressChanged(object sender, ProgressChangedEventArgs e)
  36.         {
  37.             progressBar.Value = e.ProgressPercentage;
  38.             textBox.Text = e.ProgressPercentage.ToString();
  39.         }
  40.         void bgworker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
  41.         {
  42.             progressBar.Value = 0;
  43.             if (e.Cancelled)
  44.             {
  45.                 MessageBox.Show("Background task has been canceled", "info");
  46.             }
  47.             else
  48.             {
  49.                 MessageBox.Show("Background task finished", "info");
  50.             }
  51.         }
  52.         private void btnProcess_Click(object sender, RoutedEventArgs e)
  53.         {
  54.             if (!bgworker.IsBusy)
  55.             {
  56.                 bgworker.RunWorkerAsync();
  57.             }
  58.         }
  59.         private void btnCancel_Click(object sender, RoutedEventArgs e)
  60.         {
  61.             bgworker.CancelAsync();
  62.         }
  63.     }
  64. }

演示

C# 使用C#中BackgroundWorker - 图1
BackgroundWorkerExample.gif

作者：Jason_Yuan
链接：https://www.jianshu.com/p/b89f39c5f803
来源：简书
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