Windows Dev Center

BackgroundWorker Class

Runs an operation on a separate thread.


Namespace:  System.ComponentModel
Assembly:  System (in System.dll)

Public Class BackgroundWorker

The BackgroundWorker type exposes the following members.

Public methodBackgroundWorkerInitializes a new instance of the BackgroundWorker class.

Public propertyCancellationPendingGets a value that indicates whether the application has requested cancellation of a background operation.
Public propertyIsBusyGets a value that indicates whether the BackgroundWorker is running a background operation.
Public propertyWorkerReportsProgressGets or sets a value that indicates whether the BackgroundWorker can report progress updates.
Public propertyWorkerSupportsCancellationGets or sets a value that indicates whether the BackgroundWorker supports asynchronous cancellation.

Public methodCancelAsyncRequests cancellation of a pending background operation.
Public methodEquals(Object)Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.)
Public methodGetHashCodeServes as a hash function for a particular type. (Inherited from Object.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Protected methodOnDoWorkRaises the DoWork event.
Protected methodOnProgressChangedRaises the ProgressChanged event.
Protected methodOnRunWorkerCompletedRaises the RunWorkerCompleted event.
Public methodReportProgress(Int32)Raises the ProgressChanged event.
Public methodReportProgress(Int32, Object)Raises the ProgressChanged event.
Public methodRunWorkerAsyncStarts running a background operation.
Public methodRunWorkerAsync(Object)Starts running a background operation and includes a parameter for use by the background operation.
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)

Public eventDoWorkOccurs when RunWorkerAsync is called.
Public eventProgressChangedOccurs when ReportProgress is called.
Public eventRunWorkerCompletedOccurs when the background operation has completed, has been canceled, or has raised an exception.

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.


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 for Windows Phone 8.

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 PhoneApplicationPage
    Private bw As BackgroundWorker = New BackgroundWorker

    Public Sub New()

        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
        End If
    End Sub
    Private Sub buttonCancel_Click(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs)
        If bw.WorkerSupportsCancellation = True Then
        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
                ' Perform a time consuming operation and report progress.
                bw.ReportProgress(i * 10)
            End If
    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
            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

<phone:PhoneApplicationPage x:Class="SL_BackgroundWorker_CS.Page"
    FontFamily="{StaticResource PhoneFontFamilyNormal}"
    FontSize="{StaticResource PhoneFontSizeNormal}"
    Foreground="{StaticResource PhoneForegroundBrush}"
    SupportedOrientations="Portrait" Orientation="Portrait"
    mc:Ignorable="d" d:DesignHeight="768" d:DesignWidth="480"
    <Grid x:Name="LayoutRoot" Background="Transparent">
            <StackPanel Orientation="Horizontal" 
                        HorizontalAlignment="Left" VerticalAlignment="Top" 
                        Margin="10" >
                <Button x:Name="buttonStart" Content="Start" Click="buttonStart_Click"
                        Width="200" />
                <Button x:Name="buttonCancel" Content="Cancel" Click="buttonCancel_Click"
                        Width="200" />
            <StackPanel Margin="10,50,0,0" Orientation="Horizontal">
                <TextBlock Text="Progress: " />
                <TextBlock x:Name="tbProgress" />

Windows Phone OS

Supported in: 8.1, 8.0, 7.1, 7.0

Windows Phone

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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