BackgroundWorker Class

 

Executes an operation on a separate thread.

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

System.Object
  System.MarshalByRefObject
    System.ComponentModel.Component
      System.ComponentModel.BackgroundWorker

[<HostProtectionAttribute(SecurityAction.LinkDemand, SharedState = true)>]
type BackgroundWorker = 
    class
        inherit Component
    end

NameDescription
System_CAPS_pubmethodBackgroundWorker()

Initializes a new instance of the BackgroundWorker class.

NameDescription
System_CAPS_pubpropertyCancellationPending

Gets a value indicating whether the application has requested cancellation of a background operation.

System_CAPS_protpropertyCanRaiseEvents

Gets a value indicating whether the component can raise an event.(Inherited from Component.)

System_CAPS_pubpropertyContainer

Gets the IContainer that contains the Component.(Inherited from Component.)

System_CAPS_protpropertyDesignMode

Gets a value that indicates whether the Component is currently in design mode.(Inherited from Component.)

System_CAPS_protpropertyEvents

Gets the list of event handlers that are attached to this Component.(Inherited from Component.)

System_CAPS_pubpropertyIsBusy

Gets a value indicating whether the BackgroundWorker is running an asynchronous operation.

System_CAPS_pubpropertySite

Gets or sets the ISite of the Component.(Inherited from Component.)

System_CAPS_pubpropertyWorkerReportsProgress

Gets or sets a value indicating whether the BackgroundWorker can report progress updates.

System_CAPS_pubpropertyWorkerSupportsCancellation

Gets or sets a value indicating whether the BackgroundWorker supports asynchronous cancellation.

NameDescription
System_CAPS_pubmethodCancelAsync()

Requests cancellation of a pending background operation.

System_CAPS_pubmethodCreateObjRef(Type)

Creates an object that contains all the relevant information required to generate a proxy used to communicate with a remote object.(Inherited from MarshalByRefObject.)

System_CAPS_pubmethodDispose()

Releases all resources used by the Component.(Inherited from Component.)

System_CAPS_protmethodDispose(Boolean)

Releases the unmanaged resources used by the Component and optionally releases the managed resources.(Inherited from Component.)

System_CAPS_pubmethodEquals(Object)

Determines whether the specified object is equal to the current object.(Inherited from Object.)

System_CAPS_protmethodFinalize()

Releases unmanaged resources and performs other cleanup operations before the Component is reclaimed by garbage collection.(Inherited from Component.)

System_CAPS_pubmethodGetHashCode()

Serves as the default hash function. (Inherited from Object.)

System_CAPS_pubmethodGetLifetimeService()

Retrieves the current lifetime service object that controls the lifetime policy for this instance.(Inherited from MarshalByRefObject.)

System_CAPS_protmethodGetService(Type)

Returns an object that represents a service provided by the Component or by its Container.(Inherited from Component.)

System_CAPS_pubmethodGetType()

Gets the Type of the current instance.(Inherited from Object.)

System_CAPS_pubmethodInitializeLifetimeService()

Obtains a lifetime service object to control the lifetime policy for this instance.(Inherited from MarshalByRefObject.)

System_CAPS_protmethodMemberwiseClone()

Creates a shallow copy of the current Object.(Inherited from Object.)

System_CAPS_protmethodMemberwiseClone(Boolean)

Creates a shallow copy of the current MarshalByRefObject object.(Inherited from MarshalByRefObject.)

System_CAPS_protmethodOnDoWork(DoWorkEventArgs)

Raises the DoWork event.

System_CAPS_protmethodOnProgressChanged(ProgressChangedEventArgs)

Raises the ProgressChanged event.

System_CAPS_protmethodOnRunWorkerCompleted(RunWorkerCompletedEventArgs)

Raises the RunWorkerCompleted event.

System_CAPS_pubmethodReportProgress(Int32)

Raises the ProgressChanged event.

System_CAPS_pubmethodReportProgress(Int32, Object)

Raises the ProgressChanged event.

System_CAPS_pubmethodRunWorkerAsync()

Starts execution of a background operation.

System_CAPS_pubmethodRunWorkerAsync(Object)

Starts execution of a background operation.

System_CAPS_pubmethodToString()

Returns a String containing the name of the Component, if any. This method should not be overridden.(Inherited from Component.)

NameDescription
System_CAPS_pubeventDisposed

Occurs when the component is disposed by a call to the Dispose method. (Inherited from Component.)

System_CAPS_pubeventDoWork

Occurs when RunWorkerAsync is called.

System_CAPS_pubeventProgressChanged

Occurs when ReportProgress is called.

System_CAPS_pubeventRunWorkerCompleted

Occurs 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 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, the BackgroundWorker class provides a convenient solution.

To execute a time-consuming operation in the background, create a BackgroundWorker and listen for events that report the progress of your operation and signal when your operation is finished. You can create the BackgroundWorker programmatically or you can drag it onto your form from the Components tab of the Toolbox. If you create the BackgroundWorker in the Windows Forms Designer, it will appear in the Component Tray, and its properties will be displayed in the Properties window.

To set up for a background operation, add an event handler for the DoWork event. Call your time-consuming operation in this event handler. To start the operation, call RunWorkerAsync. To receive notifications of progress updates, handle the ProgressChanged event. To receive a notification when the operation is completed, handle the RunWorkerCompleted event.

System_CAPS_noteNote

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.

BackgroundWorker events are not marshaled across AppDomain boundaries. Do not use a BackgroundWorker component to perform multithreaded operations in more than one AppDomain.

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: Run an Operation in the Background.

The following code example demonstrates the basics of the BackgroundWorker class for executing a time-consuming operation asynchronously. The following illustration shows an example of the output.

BackgroundWorker simple example

To try this code, create a Windows Forms application. Add a Label control named resultLabel and add two Button controls named startAsyncButton and cancelAsyncButton. Create Click event handlers for both buttons. From the Components tab of the Toolbox, add a BackgroundWorker component named backgroundWorker1. Create DoWork, ProgressChanged, and RunWorkerCompleted event handlers for the BackgroundWorker. In the code for the form, replace the existing code with the following code.

No code example is currently available or this language may not be supported.

The following code example demonstrates the use of the BackgroundWorker class for executing a time-consuming operation asynchronously. The following illustration shows an example of the output.

BackgroundWorker Fibonacci example

The operation computes the selected Fibonacci number, reports progress updates as the calculation proceeds, and permits a pending calculation to be canceled.

No code example is currently available or this language may not be supported.

Universal Windows Platform
Available since 10
.NET Framework
Available since 2.0
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0

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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