Runs an operation on a separate thread.
(in System.dll)
Visual Basic (Declaration)
Public Class BackgroundWorker
Dim instance As BackgroundWorker
public class BackgroundWorker
The BackgroundWorker class allows you to run an operation on a separate, dedicated thread. Time-consuming operations, such as downloads and database transactions, can cause your user interface to stop responding. When you want a responsive user interface and you must perform time-consuming operations, the BackgroundWorker class provides a convenient solution.
To run an operation in the background, create a BackgroundWorker. You can listen for events that report the progress of your operation and signal when your operation is completed.
To set up a background operation, add an event handler for the DoWork event. Call your time-consuming operation in this event handler. To start the background operation, call the RunWorkerAsync method. To receive notifications of progress updates, handle the ProgressChanged event. To receive a notification when the operation is completed, handle the RunWorkerCompleted event.
.gif) Note: |
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You must be careful not to manipulate any user-interface objects in your DoWork event handler. Instead, communicate to the user interface through the ProgressChanged and RunWorkerCompleted events. |
If your background operation requires a parameter, call RunWorkerAsync with your parameter. Inside the DoWork event handler, you can extract the parameter from the DoWorkEventArgs..::.Argument property.
For more information about BackgroundWorker, see How to: Use a Background Worker.
The following code example demonstrates the use of the BackgroundWorker class for running a time-consuming operation asynchronously. The time-consuming operation is simulated by calling the background thread's Sleep method. The example periodically reports progress and permits the operation to be canceled.
Imports System.ComponentModel
Partial Public Class Page
Inherits UserControl
Private bw As BackgroundWorker = New BackgroundWorker
Public Sub New()
InitializeComponent()
bw.WorkerReportsProgress = True
bw.WorkerSupportsCancellation = True
AddHandler bw.DoWork, AddressOf bw_DoWork
AddHandler bw.ProgressChanged, AddressOf bw_ProgressChanged
AddHandler bw.RunWorkerCompleted, AddressOf bw_RunWorkerCompleted
End Sub
Private Sub buttonStart_Click(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs)
If Not bw.IsBusy = True Then
bw.RunWorkerAsync()
End If
End Sub
Private Sub buttonCancel_Click(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs)
If bw.WorkerSupportsCancellation = True Then
bw.CancelAsync()
End If
End Sub
Private Sub bw_DoWork(ByVal sender As Object, ByVal e As DoWorkEventArgs)
Dim worker As BackgroundWorker = CType(sender, BackgroundWorker)
For i = 1 To 10
If bw.CancellationPending = True Then
e.Cancel = True
Exit For
Else
' Perform a time consuming operation and report progress.
System.Threading.Thread.Sleep(500)
bw.ReportProgress(i * 10)
End If
Next
End Sub
Private Sub bw_RunWorkerCompleted(ByVal sender As Object, ByVal e As RunWorkerCompletedEventArgs)
If e.Cancelled = True Then
Me.tbProgress.Text = "Canceled!"
ElseIf e.Error IsNot Nothing Then
Me.tbProgress.Text = "Error: " & e.Error.Message
Else
Me.tbProgress.Text = "Done!"
End If
End Sub
Private Sub bw_ProgressChanged(ByVal sender As Object, ByVal e As ProgressChangedEventArgs)
Me.tbProgress.Text = e.ProgressPercentage.ToString() & "%"
End Sub
End Class
using System.ComponentModel;
using System.Windows;
using System.Windows.Controls;
namespace SL_BackgroundWorker_CS
{
public partial class Page : UserControl
{
private BackgroundWorker bw = new BackgroundWorker();
public Page()
{
InitializeComponent();
bw.WorkerReportsProgress = true;
bw.WorkerSupportsCancellation = true;
bw.DoWork += new DoWorkEventHandler(bw_DoWork);
bw.ProgressChanged += new ProgressChangedEventHandler(bw_ProgressChanged);
bw.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bw_RunWorkerCompleted);
}
private void buttonStart_Click(object sender, RoutedEventArgs e)
{
if (bw.IsBusy != true)
{
bw.RunWorkerAsync();
}
}
private void buttonCancel_Click(object sender, RoutedEventArgs e)
{
if (bw.WorkerSupportsCancellation == true)
{
bw.CancelAsync();
}
}
private void bw_DoWork(object sender, DoWorkEventArgs e)
{
BackgroundWorker worker = sender as BackgroundWorker;
for (int i = 1; (i <= 10); i++)
{
if ((worker.CancellationPending == true))
{
e.Cancel = true;
break;
}
else
{
// Perform a time consuming operation and report progress.
System.Threading.Thread.Sleep(500);
worker.ReportProgress((i * 10));
}
}
}
private void bw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
if ((e.Cancelled == true))
{
this.tbProgress.Text = "Canceled!";
}
else if (!(e.Error == null))
{
this.tbProgress.Text = ("Error: " + e.Error.Message);
}
else
{
this.tbProgress.Text = "Done!";
}
}
private void bw_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
this.tbProgress.Text = (e.ProgressPercentage.ToString() + "%");
}
}
}
<UserControl x:Class="SL_BackgroundWorker_CS.Page"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Width="400" Height="300">
<Grid x:Name="LayoutRoot" Background="White">
<StackPanel Height="30" Orientation="Horizontal"
HorizontalAlignment="Left" VerticalAlignment="Top"
Margin="10" >
<Button x:Name="buttonStart" Content="Start" Click="buttonStart_Click"
Width="80" Height="30"/>
<Button x:Name="buttonCancel" Content="Cancel" Click="buttonCancel_Click"
Width="80" Height="30"/>
</StackPanel>
<StackPanel Margin="10,50,0,0" Orientation="Horizontal">
<TextBlock Text="Progress: "/>
<TextBlock x:Name="tbProgress"/>
</StackPanel>
</Grid>
</UserControl>
<UserControl x:Class="SL_BackgroundWorker_VB.Page"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Width="400" Height="300">
<Grid x:Name="LayoutRoot" Background="White">
<StackPanel Height="30" Orientation="Horizontal"
HorizontalAlignment="Left" VerticalAlignment="Top"
Margin="10" >
<Button x:Name="buttonStart" Content="Start" Click="buttonStart_Click"
Width="80" Height="30"/>
<Button x:Name="buttonCancel" Content="Cancel" Click="buttonCancel_Click"
Width="80" Height="30"/>
</StackPanel>
<StackPanel Margin="10,50,0,0" Orientation="Horizontal">
<TextBlock Text="Progress: " />
<TextBlock x:Name="tbProgress" />
</StackPanel>
</Grid>
</UserControl>
System..::.Object
System.ComponentModel..::.BackgroundWorker
Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.
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