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BackgroundWorker (Clase)

Nota: esta clase es nueva en la versión 2.0 de .NET Framework.

Ejecuta una operación en un subproceso independiente.

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

public class BackgroundWorker : Component
public class BackgroundWorker extends Component
public class BackgroundWorker extends Component

La clase BackgroundWorker permite ejecutar una operación en un subproceso dedicado e independiente. Durante la ejecución de operaciones que exigen mucho tiempo, como las descargas y las transacciones de las bases de datos, puede parecer que la interfaz de usuario (UI) ha dejado de responder. Cuando se necesita una interfaz de usuario rápida, pero se producen largos retrasos asociados a tales operaciones, la clase BackgroundWorker ofrece una práctica solución.

Para ejecutar en segundo plano una operación que exija mucho tiempo, cree un objeto BackgroundWorker y realice escuchas de eventos que creen informes del progreso de la operación y que señalen su finalización. Se puede crear BackgroundWorker mediante programación o arrastrarlo al formulario desde la ficha Componentes del Cuadro de herramientas. Si crea BackgroundWorker en el Diseñador de Windows Forms, aparecerá en la Bandeja de componentes y sus propiedades se mostrarán en la ventana Propiedades.

Para configurar una operación en segundo plano, agregue un controlador de eventos para el evento DoWork. En este controlador de eventos, llame a la operación que requiere mucho tiempo. Para iniciar la operación, llame a RunWorkerAsync. Para recibir notificaciones sobre las actualizaciones de progreso, controle el evento ProgressChanged. Para recibir una notificación cuando finalice la operación, controle el evento RunWorkerCompleted.

NotaNota

Tenga cuidado para no manipular ningún objeto de la interfaz de usuario en el controlador de eventos DoWork. En su lugar, comuníquese con la interfaz de usuario a través de los eventos ProgressChanged y RunWorkerCompleted.

No se calculan referencias a los eventos BackgroundWorker a través de los límites de AppDomain. No utilice un componente BackgroundWorker para realizar operaciones multiproceso en más de un objeto AppDomain.

Si la operación en segundo plano requiere un parámetro, llame a RunWorkerAsync con el parámetro. Dentro del controlador de eventos DoWork, puede extraer el parámetro de la propiedad DoWorkEventArgs.Argument.

Para obtener más información sobre BackgroundWorker, vea Cómo: Ejecutar una operación en segundo plano.

NotaNota

El atributo HostProtectionAttribute aplicado a esta clase tiene el siguiente valor para la propiedad Resources: SharedState. HostProtectionAttribute no afecta a las aplicaciones de escritorio (que normalmente se inician al hacer doble clic en un icono, escribir un comando o introducir una dirección URL en un explorador). Para obtener más información, vea la clase HostProtectionAttribute o Programación de SQL Server y atributos de protección del host.

En el ejemplo de código siguiente se muestra el uso de la clase BackgroundWorker para ejecutar de forma asincrónica una operación que requiere mucho tiempo. La operación calcula el número de Fibonacci seleccionado, crea informes sobre las actualizaciones de progreso mientras se realiza el cálculo y permite la cancelación de un cálculo pendiente.

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();

            InitializeBackgoundWorker();
        }

        // Set up the BackgroundWorker object by 
        // attaching event handlers. 
        private void InitializeBackgoundWorker()
        {
            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());
        }
    }
}


import System.* ;
import System.Collections.* ;
import System.ComponentModel.* ;
import System.Drawing.* ;
import System.Threading.* ;
import System.Windows.Forms.* ;

public class FibonacciForm extends 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();
        InitializeBackgoundWorker();
    } //FibonacciForm

    // Set up the BackgroundWorker object by 
    // attaching event handlers. 
    private void InitializeBackgoundWorker()
    {
        backgroundWorker1.add_DoWork(new DoWorkEventHandler(
            backgroundWorker1_DoWork));
        backgroundWorker1.add_RunWorkerCompleted(
            new RunWorkerCompletedEventHandler(
            backgroundWorker1_RunWorkerCompleted));
        backgroundWorker1.add_ProgressChanged(
            new ProgressChangedEventHandler(backgroundWorker1_ProgressChanged));
    } //InitializeBackgoundWorker

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

        // Disable the UpDown control until 
        // the asynchronous operation is done.
        this.numericUpDown1.set_Enabled(false);

        // Disable the Start button until 
        // the asynchronous operation is done.
        this.startAsyncButton.set_Enabled(false);

        // Enable the Cancel button while 
        // the asynchronous operation runs.
        this.cancelAsyncButton.set_Enabled(true);

        // Get the value from the UpDown control.
        numberToCompute = System.Convert.ToInt32((numericUpDown1.get_Value()));

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

        // Start the asynchronous operation.
        backgroundWorker1.RunWorkerAsync(System.Convert.ToString
            (numberToCompute));
    }
    
    private void cancelAsyncButton_Click(Object sender, System.EventArgs e)
    {   
        // Cancel the asynchronous operation.
        this.backgroundWorker1.CancelAsync();

        // Disable the Cancel button.
        cancelAsyncButton.set_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 = (BackgroundWorker)sender;

        // Assign the result of the computation
        // to the Result property of the DoWorkEventArgs
        // object. This is will be available to the 
        // RunWorkerCompleted eventhandler.
        e.set_Result(new Long(ComputeFibonacci(System.Convert.ToInt32
            (e.get_Argument()), worker, e)));
        //e.Result = ComputeFibonacci((int)e.Argument, worker, e); 
    } //backgroundWorker1_DoWork

    // 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.get_Error() != null) {
        
            MessageBox.Show(e.get_Error().get_Message());
        }
        else {
        
            if (e.get_Cancelled()) {
            
                // Next, handle the case where the user cancelled 
                // 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.set_Text("Cancelled");
            }
            else {
            
                // Finally, handle the case where the operation 
                // succeeded.
                resultLabel.set_Text(e.get_Result().ToString());
            }
        }

        // Enable the UpDown control.
        this.numericUpDown1.set_Enabled(true);

        // Enable the Start button.
        startAsyncButton.set_Enabled(true);

        // Disable the Cancel button.
        cancelAsyncButton.set_Enabled(false);
    } //backgroundWorker1_RunWorkerCompleted

    // This event handler updates the progress bar.
    private void backgroundWorker1_ProgressChanged(Object sender,
        ProgressChangedEventArgs e)
    {
        this.progressBar1.set_Value(e.get_ProgressPercentage());
    } //backgroundWorker1_ProgressChanged

    // 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 cancelled.
        // 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.get_CancellationPending()) {
        
            e.set_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.set_Location(new System.Drawing.Point(16, 16));
        this.numericUpDown1.set_Maximum(new System.Decimal(
            new int[] { 91, 0, 0, 0 }));
        this.numericUpDown1.set_Minimum(new System.Decimal(
            new int[] { 1, 0, 0, 0 }));
        this.numericUpDown1.set_Name("numericUpDown1");
        this.numericUpDown1.set_Size(new System.Drawing.Size(80, 20));
        this.numericUpDown1.set_TabIndex(0);
        this.numericUpDown1.set_Value(new System.Decimal(
            new int[] { 1, 0, 0, 0 }));

        // 
        // startAsyncButton
        // 
        this.startAsyncButton.set_Location(new System.Drawing.Point(16, 72));
        this.startAsyncButton.set_Name("startAsyncButton");
        this.startAsyncButton.set_Size(new System.Drawing.Size(120, 23));
        this.startAsyncButton.set_TabIndex(1);
        this.startAsyncButton.set_Text("Start Async");
        this.startAsyncButton.add_Click(
            new System.EventHandler(this.startAsyncButton_Click));

        // 
        // cancelAsyncButton
        // 
        this.cancelAsyncButton.set_Enabled(false);
        this.cancelAsyncButton.set_Location(new System.Drawing.Point(153, 72));
        this.cancelAsyncButton.set_Name("cancelAsyncButton");
        this.cancelAsyncButton.set_Size(new System.Drawing.Size(119, 23));
        this.cancelAsyncButton.set_TabIndex(2);
        this.cancelAsyncButton.set_Text("Cancel Async");
        this.cancelAsyncButton.add_Click(
            new System.EventHandler(this.cancelAsyncButton_Click));

        // 
        // resultLabel
        // 
        this.resultLabel.set_BorderStyle(System.Windows.Forms.BorderStyle.Fixed3D);
        this.resultLabel.set_Location(new System.Drawing.Point(112, 16));
        this.resultLabel.set_Name("resultLabel");
        this.resultLabel.set_Size(new System.Drawing.Size(160, 23));
        this.resultLabel.set_TabIndex(3);
        this.resultLabel.set_Text("(no result)");
        this.resultLabel.set_TextAlign(System.Drawing.ContentAlignment.MiddleCenter);

        // 
        // progressBar1
        // 
        this.progressBar1.set_Location(new System.Drawing.Point(18, 48));
        this.progressBar1.set_Name("progressBar1");
        this.progressBar1.set_Size(new System.Drawing.Size(256, 8));
        this.progressBar1.set_Step(2);
        this.progressBar1.set_TabIndex(4);

        // 
        // backgroundWorker1
        // 
        this.backgroundWorker1.set_WorkerReportsProgress(true);
        this.backgroundWorker1.set_WorkerSupportsCancellation(true);

        // 
        // FibonacciForm
        // 
        this.set_ClientSize(new System.Drawing.Size(292, 118));
        this.get_Controls().Add(this.progressBar1);
        this.get_Controls().Add(this.resultLabel);
        this.get_Controls().Add(this.cancelAsyncButton);
        this.get_Controls().Add(this.startAsyncButton);
        this.get_Controls().Add(this.numericUpDown1);
        this.set_Name("FibonacciForm");
        this.set_Text("Fibonacci Calculator");
        ((System.ComponentModel.ISupportInitialize)(this.numericUpDown1)).
            EndInit();
        this.ResumeLayout(false);
    } //InitializeComponent
    #endregion

    /** @attribute STAThread()
     */
    public static void main(String[] args)
    {
        Application.Run(new FibonacciForm());
    } //main
} //FibonacciForm
   

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

Los miembros estáticos públicos (Shared en Visual Basic) de este tipo son seguros para la ejecución de subprocesos. No se garantiza que los miembros de instancias sean seguros para la ejecución de subprocesos.

Windows 98, Windows 2000 SP4, Windows Millennium, Windows Server 2003, Windows XP Media Center, Windows XP Professional x64, Windows XP SP2, Windows XP Starter Edition

.NET Framework no admite todas las versiones de cada plataforma. Para obtener una lista de las versiones admitidas, vea Requisitos del sistema.

.NET Framework

Compatible con: 2.0
Mostrar: