2.2 BackgroundWorker的使用介绍

        BackgroundWorker 是 .NET Framework 中一个简化异步操作的组件，它位于 System.ComponentModel 命名空间下。它为开发人员提供了一种简单的方式在后台执行耗时操作，同时保持与 UI 线程的交互

主要属性以及任务如下：

• DoWork 事件：在后台线程中执行耗时操作：（不能直接调用UI控件）

• RunWorkerAsync 方法：启动后台操作

• ReportProgress 方法：报告操作进度

• ProgressChanged 事件：当进度更新时触发：（可以直接调用UI控件）

• RunWorkerCompleted 事件：当操作完成时触发（可以直接调用UI控件）

• CancellationPending 属性：检查是否请求取消

• CancelAsync 方法：请求取消操作

• IsBusy 属性：指示是否正在运行后台操作

• 注意事项：

1. 在 DoWork 事件处理程序中不要直接访问UI控件

2. 如果需要传递数据，可以使用 RunWorkerAsync(object) 和 DoWorkEventArgs.Argument

3. 结果可以通过 RunWorkerCompletedEventArgs.Result 传递回UI线程

例如：下面是一个wpf的小例子，仿真了开始，取消，以及汇报进度的功能。

 public partial class BackgroundDemo : Window
 {
     BackgroundWorker bw;
     public BackgroundDemo()
     {
         InitializeComponent();
         bw = new BackgroundWorker();
         bw.WorkerReportsProgress = true;
         bw.WorkerSupportsCancellation = true;
         bw.DoWork += Bw_DoWork;
         bw.ProgressChanged += Bw_ProgressChanged;
         bw.RunWorkerCompleted += Bw_RunWorkerCompleted;
         btnCancel.IsEnabled = false;
     }

     private void Bw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
     {
         pbPercent.Value = 100;
         this.btnCancel.IsEnabled = false;
         this.btnStart.IsEnabled = true;
         
         if(e.Error!=null)
         {
             this.tbInfo.Text = "异常" + e.Error.Message;
         }
         else if(e.Cancelled)
         {
             this.tbInfo.Text = "被取消";
         }
         else
         {
             this.tbInfo.Text = "正常完成";
         }
     }

     private void Bw_ProgressChanged(object sender, ProgressChangedEventArgs e)
     {
         this.pbPercent.Value = e.ProgressPercentage;
     }

     private void Bw_DoWork(object sender, DoWorkEventArgs e)
     {
         int timer =(int) e.Argument;
         if (timer <= 0) timer = 20;
         for(int i=0;i<timer;i++)
         {
             if(bw.CancellationPending)
             {
                 e.Cancel = true;
                 break;
             }
             Thread.Sleep(1000);
             bw.ReportProgress(  i*100 / timer);

         }
     }

     private void btnStart_Click(object sender, RoutedEventArgs e)
     {
         this.btnStart.IsEnabled = false;
         this.btnCancel.IsEnabled = true;
         bw.RunWorkerAsync(10);  //运行20秒
         this.tbInfo.Text = "开始计时中";
     }

     private void btnCancel_Click(object sender, RoutedEventArgs e)
     {
         bw.CancelAsync();
     }
 }

<Window x:Class="AHui_ProjectManager.Model.BackgroundDemo"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:AHui_ProjectManager.Model"
        mc:Ignorable="d"
        Title="BackgroundDemo" Height="450" Width="800">
    <Grid>

        <TextBlock x:Name="tbInfo" HorizontalAlignment="Left" Height="23"  Background="LightBlue"
                 Margin="0,50,0,0" VerticalAlignment="top" Width="381"/>
        <ProgressBar x:Name="pbPercent" HorizontalAlignment="Left" Height="23" 
                 Margin="0,90,0,0" VerticalAlignment="top" Width="381"/>
        <Button x:Name="btnStart" Content="开始" HorizontalAlignment="Left" Height="23" 
                 Margin="0,135,0,0" VerticalAlignment="top" Width="60" Click="btnStart_Click"/>
        
        <Button x:Name="btnCancel" Content="取消"  HorizontalAlignment="Left" Height="23" 
         Margin="306,135,0,0" VerticalAlignment="top" Width="60" Click="btnCancel_Click"/>
    </Grid>
</Window>