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Clase BackgroundWorker

 

Publicado: octubre de 2016

Ejecuta una operación en un subproceso distinto.

Espacio de nombres:   System.ComponentModel
Ensamblado:  System (en System.dll)

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

[HostProtectionAttribute(SecurityAction.LinkDemand, SharedState = true)]
public class BackgroundWorker : Component

NombreDescripción
System_CAPS_pubmethodBackgroundWorker()

Inicializa una nueva instancia de la clase BackgroundWorker.

NombreDescripción
System_CAPS_pubpropertyCancellationPending

Obtiene un valor que indica si la aplicación ha solicitado la cancelación de una operación en segundo plano.

System_CAPS_protpropertyCanRaiseEvents

Obtiene un valor que indica si el componente puede provocar un evento.(Heredado de Component).

System_CAPS_pubpropertyContainer

Obtiene IContainer que contiene Component.(Heredado de Component).

System_CAPS_protpropertyDesignMode

Obtiene un valor que indica si la Component está actualmente en modo de diseño.(Heredado de Component).

System_CAPS_protpropertyEvents

Obtiene la lista de controladores de eventos que se adjuntará a este Component.(Heredado de Component).

System_CAPS_pubpropertyIsBusy

Obtiene un valor que indica si la BackgroundWorker está ejecutando una operación asincrónica.

System_CAPS_pubpropertySite

Obtiene o establece la ISite de la Component.(Heredado de Component).

System_CAPS_pubpropertyWorkerReportsProgress

Obtiene o establece un valor que indica si la BackgroundWorker puede informar de las actualizaciones de progreso.

System_CAPS_pubpropertyWorkerSupportsCancellation

Obtiene o establece un valor que indica si la BackgroundWorker admite la cancelación asincrónica.

NombreDescripción
System_CAPS_pubmethodCancelAsync()

Solicita la cancelación de una operación en segundo plano pendiente.

System_CAPS_pubmethodCreateObjRef(Type)

Crea un objeto que contiene toda la información relevante necesaria para generar a un proxy que se utiliza para comunicarse con un objeto remoto.(Heredado de MarshalByRefObject).

System_CAPS_pubmethodDispose()

Libera todos los recursos que usa Component.(Heredado de Component).

System_CAPS_protmethodDispose(Boolean)

Libera los recursos no administrados que usa Component y libera los recursos administrados de forma opcional.(Heredado de Component).

System_CAPS_pubmethodEquals(Object)

Determina si el objeto especificado es igual al objeto actual.(Heredado de Object).

System_CAPS_protmethodFinalize()

Libera recursos no administrados y realiza otras operaciones de limpieza antes de que se reclame el elemento Component durante la recolección de elementos no usados.(Heredado de Component).

System_CAPS_pubmethodGetHashCode()

Sirve como la función hash predeterminada.(Heredado de Object).

System_CAPS_pubmethodGetLifetimeService()

Recupera el objeto de servicio de duración actual que controla la directiva de duración de esta instancia.(Heredado de MarshalByRefObject).

System_CAPS_protmethodGetService(Type)

Devuelve un objeto que representa el servicio suministrado por Component o por Container.(Heredado de Component).

System_CAPS_pubmethodGetType()

Obtiene el Type de la instancia actual.(Heredado de Object).

System_CAPS_pubmethodInitializeLifetimeService()

Obtiene un objeto de servicio de duración para controlar la directiva de duración de esta instancia.(Heredado de MarshalByRefObject).

System_CAPS_protmethodMemberwiseClone()

Crea una copia superficial del Object actual.(Heredado de Object).

System_CAPS_protmethodMemberwiseClone(Boolean)

Crea una copia superficial del elemento actual MarshalByRefObject objeto.(Heredado de MarshalByRefObject).

System_CAPS_protmethodOnDoWork(DoWorkEventArgs)

Genera el evento DoWork.

System_CAPS_protmethodOnProgressChanged(ProgressChangedEventArgs)

Genera el evento ProgressChanged.

System_CAPS_protmethodOnRunWorkerCompleted(RunWorkerCompletedEventArgs)

Genera el evento RunWorkerCompleted.

System_CAPS_pubmethodReportProgress(Int32)

Genera el evento ProgressChanged.

System_CAPS_pubmethodReportProgress(Int32, Object)

Genera el evento ProgressChanged.

System_CAPS_pubmethodRunWorkerAsync()

Inicia la ejecución de una operación en segundo plano.

System_CAPS_pubmethodRunWorkerAsync(Object)

Inicia la ejecución de una operación en segundo plano.

System_CAPS_pubmethodToString()

Devuelve un String que contiene el nombre de la Component, si existe. Este método no se debe invalidar.(Heredado de Component).

NombreDescripción
System_CAPS_pubeventDisposed

Se produce cuando el componente se elimina mediante una llamada a la Dispose (método).(Heredado de Component).

System_CAPS_pubeventDoWork

Se produce cuando RunWorkerAsync se llama.

System_CAPS_pubeventProgressChanged

Se produce cuando ReportProgress se llama.

System_CAPS_pubeventRunWorkerCompleted

Se produce cuando la operación en segundo plano se ha completado, se ha cancelado o ha producido una excepción.

The T:System.ComponentModel.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 T:System.ComponentModel.BackgroundWorker class provides a convenient solution.

To execute a time-consuming operation in the background, create a T:System.ComponentModel.BackgroundWorker and listen for events that report the progress of your operation and signal when your operation is finished. You can create the T:System.ComponentModel.BackgroundWorker programmatically or you can drag it onto your form from the Components tab of the Toolbox. If you create the T:System.ComponentModel.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 E:System.ComponentModel.BackgroundWorker.DoWork event. Call your time-consuming operation in this event handler. To start the operation, call M:System.ComponentModel.BackgroundWorker.RunWorkerAsync. To receive notifications of progress updates, handle the E:System.ComponentModel.BackgroundWorker.ProgressChanged event. To receive a notification when the operation is completed, handle the E:System.ComponentModel.BackgroundWorker.RunWorkerCompleted event.

System_CAPS_noteNota

You must be careful not to manipulate any user-interface objects in your E:System.ComponentModel.BackgroundWorker.DoWork event handler. Instead, communicate to the user interface through the E:System.ComponentModel.BackgroundWorker.ProgressChanged and E:System.ComponentModel.BackgroundWorker.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 M:System.ComponentModel.BackgroundWorker.RunWorkerAsync with your parameter. Inside the E:System.ComponentModel.BackgroundWorker.DoWork event handler, you can extract the parameter from the P:System.ComponentModel.DoWorkEventArgs.Argument property.

For more information about T:System.ComponentModel.BackgroundWorker, see How to: Run an Operation in the Background.

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

Ejemplo sencillo de la clase BackgroundWorker

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

using System;
using System.ComponentModel;
using System.Windows.Forms;

namespace BackgroundWorkerSimple
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            backgroundWorker1.WorkerReportsProgress = true;
            backgroundWorker1.WorkerSupportsCancellation = true;
        }

        private void startAsyncButton_Click(object sender, EventArgs e)
        {
            if (backgroundWorker1.IsBusy != true)
            {
                // Start the asynchronous operation.
                backgroundWorker1.RunWorkerAsync();
            }
        }

        private void cancelAsyncButton_Click(object sender, EventArgs e)
        {
            if (backgroundWorker1.WorkerSupportsCancellation == true)
            {
                // Cancel the asynchronous operation.
                backgroundWorker1.CancelAsync();
            }
        }

        // This event handler is where the time-consuming work is done.
        private void backgroundWorker1_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);
                }
            }
        }

        // This event handler updates the progress.
        private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
        {
            resultLabel.Text = (e.ProgressPercentage.ToString() + "%");
        }

        // This event handler deals with the results of the background operation.
        private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            if (e.Cancelled == true)
            {
                resultLabel.Text = "Canceled!";
            }
            else if (e.Error != null)
            {
                resultLabel.Text = "Error: " + e.Error.Message;
            }
            else
            {
                resultLabel.Text = "Done!";
            }
        }
    }
}

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

Ejemplo de Fibonacci de la clase BackgroundWorker

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

using System;
using System.Collections;
using System.ComponentModel;
using System.Drawing;
using System.Threading;
using System.Windows.Forms;

namespace BackgroundWorkerExample
{	
    public class FibonacciForm : System.Windows.Forms.Form
    {	
        private int numberToCompute = 0;
        private int highestPercentageReached = 0;

        private System.Windows.Forms.NumericUpDown numericUpDown1;
        private System.Windows.Forms.Button startAsyncButton;
        private System.Windows.Forms.Button cancelAsyncButton;
        private System.Windows.Forms.ProgressBar progressBar1;
        private System.Windows.Forms.Label resultLabel;
        private System.ComponentModel.BackgroundWorker backgroundWorker1;

        public FibonacciForm()
        {	
            InitializeComponent();

            InitializeBackgroundWorker();
        }

        // Set up the BackgroundWorker object by 
        // attaching event handlers. 
        private void InitializeBackgroundWorker()
        {
            backgroundWorker1.DoWork += 
                new DoWorkEventHandler(backgroundWorker1_DoWork);
            backgroundWorker1.RunWorkerCompleted += 
                new RunWorkerCompletedEventHandler(
            backgroundWorker1_RunWorkerCompleted);
            backgroundWorker1.ProgressChanged += 
                new ProgressChangedEventHandler(
            backgroundWorker1_ProgressChanged);
        }

        private void startAsyncButton_Click(System.Object sender, 
            System.EventArgs e)
        {
            // Reset the text in the result label.
            resultLabel.Text = String.Empty;

            // Disable the UpDown control until 
            // the asynchronous operation is done.
            this.numericUpDown1.Enabled = false;

            // Disable the Start button until 
            // the asynchronous operation is done.
            this.startAsyncButton.Enabled = false;

            // Enable the Cancel button while 
            // the asynchronous operation runs.
            this.cancelAsyncButton.Enabled = true;

            // Get the value from the UpDown control.
            numberToCompute = (int)numericUpDown1.Value;

            // Reset the variable for percentage tracking.
            highestPercentageReached = 0;

            // Start the asynchronous operation.
            backgroundWorker1.RunWorkerAsync(numberToCompute);
        }

        private void cancelAsyncButton_Click(System.Object sender, 
            System.EventArgs e)
        {   
            // Cancel the asynchronous operation.
            this.backgroundWorker1.CancelAsync();

            // Disable the Cancel button.
            cancelAsyncButton.Enabled = false;
        }

        // This event handler is where the actual,
        // potentially time-consuming work is done.
        private void backgroundWorker1_DoWork(object sender, 
            DoWorkEventArgs e)
        {   
            // Get the BackgroundWorker that raised this event.
            BackgroundWorker worker = sender as BackgroundWorker;

            // Assign the result of the computation
            // to the Result property of the DoWorkEventArgs
            // object. This is will be available to the 
            // RunWorkerCompleted eventhandler.
            e.Result = ComputeFibonacci((int)e.Argument, worker, e);
        }

        // This event handler deals with the results of the
        // background operation.
        private void backgroundWorker1_RunWorkerCompleted(
            object sender, RunWorkerCompletedEventArgs e)
        {
            // First, handle the case where an exception was thrown.
            if (e.Error != null)
            {
                MessageBox.Show(e.Error.Message);
            }
            else if (e.Cancelled)
            {
                // Next, handle the case where the user canceled 
                // the operation.
                // Note that due to a race condition in 
                // the DoWork event handler, the Cancelled
                // flag may not have been set, even though
                // CancelAsync was called.
                resultLabel.Text = "Canceled";
            }
            else
            {
                // Finally, handle the case where the operation 
                // succeeded.
                resultLabel.Text = e.Result.ToString();
            }

            // Enable the UpDown control.
            this.numericUpDown1.Enabled = true;

            // Enable the Start button.
            startAsyncButton.Enabled = true;

            // Disable the Cancel button.
            cancelAsyncButton.Enabled = false;
        }

        // This event handler updates the progress bar.
        private void backgroundWorker1_ProgressChanged(object sender,
            ProgressChangedEventArgs e)
        {
            this.progressBar1.Value = e.ProgressPercentage;
        }

        // This is the method that does the actual work. For this
        // example, it computes a Fibonacci number and
        // reports progress as it does its work.
        long ComputeFibonacci(int n, BackgroundWorker worker, DoWorkEventArgs e)
        {
            // The parameter n must be >= 0 and <= 91.
            // Fib(n), with n > 91, overflows a long.
            if ((n < 0) || (n > 91))
            {
                throw new ArgumentException(
                    "value must be >= 0 and <= 91", "n");
            }

            long result = 0;

            // Abort the operation if the user has canceled.
            // Note that a call to CancelAsync may have set 
            // CancellationPending to true just after the
            // last invocation of this method exits, so this 
            // code will not have the opportunity to set the 
            // DoWorkEventArgs.Cancel flag to true. This means
            // that RunWorkerCompletedEventArgs.Cancelled will
            // not be set to true in your RunWorkerCompleted
            // event handler. This is a race condition.

            if (worker.CancellationPending)
            {   
                e.Cancel = true;
            }
            else
            {   
                if (n < 2)
                {   
                    result = 1;
                }
                else
                {   
                    result = ComputeFibonacci(n - 1, worker, e) + 
                             ComputeFibonacci(n - 2, worker, e);
                }

                // Report progress as a percentage of the total task.
                int percentComplete = 
                    (int)((float)n / (float)numberToCompute * 100);
                if (percentComplete > highestPercentageReached)
                {
                    highestPercentageReached = percentComplete;
                    worker.ReportProgress(percentComplete);
                }
            }

            return result;
        }


		#region Windows Form Designer generated code

        private void InitializeComponent()
        {
            this.numericUpDown1 = new System.Windows.Forms.NumericUpDown();
            this.startAsyncButton = new System.Windows.Forms.Button();
            this.cancelAsyncButton = new System.Windows.Forms.Button();
            this.resultLabel = new System.Windows.Forms.Label();
            this.progressBar1 = new System.Windows.Forms.ProgressBar();
            this.backgroundWorker1 = new System.ComponentModel.BackgroundWorker();
            ((System.ComponentModel.ISupportInitialize)(this.numericUpDown1)).BeginInit();
            this.SuspendLayout();
            // 
            // numericUpDown1
            // 
            this.numericUpDown1.Location = new System.Drawing.Point(16, 16);
            this.numericUpDown1.Maximum = new System.Decimal(new int[] {
            91,
            0,
            0,
            0});
            this.numericUpDown1.Minimum = new System.Decimal(new int[] {
            1,
            0,
            0,
            0});
            this.numericUpDown1.Name = "numericUpDown1";
            this.numericUpDown1.Size = new System.Drawing.Size(80, 20);
            this.numericUpDown1.TabIndex = 0;
            this.numericUpDown1.Value = new System.Decimal(new int[] {
            1,
            0,
            0,
            0});
            // 
            // startAsyncButton
            // 
            this.startAsyncButton.Location = new System.Drawing.Point(16, 72);
            this.startAsyncButton.Name = "startAsyncButton";
            this.startAsyncButton.Size = new System.Drawing.Size(120, 23);
            this.startAsyncButton.TabIndex = 1;
            this.startAsyncButton.Text = "Start Async";
            this.startAsyncButton.Click += new System.EventHandler(this.startAsyncButton_Click);
            // 
            // cancelAsyncButton
            // 
            this.cancelAsyncButton.Enabled = false;
            this.cancelAsyncButton.Location = new System.Drawing.Point(153, 72);
            this.cancelAsyncButton.Name = "cancelAsyncButton";
            this.cancelAsyncButton.Size = new System.Drawing.Size(119, 23);
            this.cancelAsyncButton.TabIndex = 2;
            this.cancelAsyncButton.Text = "Cancel Async";
            this.cancelAsyncButton.Click += new System.EventHandler(this.cancelAsyncButton_Click);
            // 
            // resultLabel
            // 
            this.resultLabel.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;
            this.resultLabel.Location = new System.Drawing.Point(112, 16);
            this.resultLabel.Name = "resultLabel";
            this.resultLabel.Size = new System.Drawing.Size(160, 23);
            this.resultLabel.TabIndex = 3;
            this.resultLabel.Text = "(no result)";
            this.resultLabel.TextAlign = System.Drawing.ContentAlignment.MiddleCenter;
            // 
            // progressBar1
            // 
            this.progressBar1.Location = new System.Drawing.Point(18, 48);
            this.progressBar1.Name = "progressBar1";
            this.progressBar1.Size = new System.Drawing.Size(256, 8);
            this.progressBar1.Step = 2;
            this.progressBar1.TabIndex = 4;
            // 
            // backgroundWorker1
            // 
            this.backgroundWorker1.WorkerReportsProgress = true;
            this.backgroundWorker1.WorkerSupportsCancellation = true;
            // 
            // FibonacciForm
            // 
            this.ClientSize = new System.Drawing.Size(292, 118);
            this.Controls.Add(this.progressBar1);
            this.Controls.Add(this.resultLabel);
            this.Controls.Add(this.cancelAsyncButton);
            this.Controls.Add(this.startAsyncButton);
            this.Controls.Add(this.numericUpDown1);
            this.Name = "FibonacciForm";
            this.Text = "Fibonacci Calculator";
            ((System.ComponentModel.ISupportInitialize)(this.numericUpDown1)).EndInit();
            this.ResumeLayout(false);

        }
		#endregion

        [STAThread]
        static void Main()
        {
            Application.Run(new FibonacciForm());
        }
    }
}

Plataforma universal de Windows
Disponible desde 10
.NET Framework
Disponible desde 2.0
Silverlight
Disponible desde 2.0
Windows Phone Silverlight
Disponible desde 7.0

Cualquier miembro ( Compartido en Visual Basic) estático público de este tipo es seguro para subprocesos. No se garantiza que los miembros de instancia sean seguros para subprocesos.

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