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 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
DoWorkProgressChanged-
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
if (worker.CancellationPending)
{
e.Cancel = true;
}
示例程序
XAML
<Window x:Class="BackgroundWorkerExample.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="150" Width="300">
<StackPanel>
<ProgressBar Name="progressBar" Height="20" Width="250" Margin="10"></ProgressBar>
<TextBox Name="textBox" Width="50" Height="20" HorizontalAlignment="Center"></TextBox>
<Button Name="btnProcess" Width="100" Click="btnProcess_Click" Margin="5">Start</Button>
<Button Name="btnCancel" Width="100" Click="btnCancel_Click" Margin="5">Cancel</Button>
</StackPanel>
</Window>
C#
namespace BackgroundWorkerExample
{
/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
public partial class MainWindow : Window
{
BackgroundWorker bgworker = new BackgroundWorker();
public MainWindow()
{
InitializeComponent();
bgworker.WorkerReportsProgress = true;
bgworker.WorkerSupportsCancellation = true;
bgworker.DoWork += bgworker_DoWork;
bgworker.ProgressChanged += bgworker_ProgressChanged;
bgworker.RunWorkerCompleted += bgworker_RunWorkerCompleted;
}
void bgworker_DoWork(object sender, DoWorkEventArgs e)
{
BackgroundWorker worker = sender as BackgroundWorker;
for (int i = 1; i <= 100; i++)
{
if (worker.CancellationPending)
{
e.Cancel = true;
}
else
{
worker.ReportProgress(i);
Thread.Sleep(100);
}
}
}
void bgworker_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
progressBar.Value = e.ProgressPercentage;
textBox.Text = e.ProgressPercentage.ToString();
}
void bgworker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
progressBar.Value = 0;
if (e.Cancelled)
{
MessageBox.Show("Background task has been canceled", "info");
}
else
{
MessageBox.Show("Background task finished", "info");
}
}
private void btnProcess_Click(object sender, RoutedEventArgs e)
{
if (!bgworker.IsBusy)
{
bgworker.RunWorkerAsync();
}
}
private void btnCancel_Click(object sender, RoutedEventArgs e)
{
bgworker.CancelAsync();
}
}
}
演示
BackgroundWorkerExample.gif
