Cómo: Ejecutar una operación en segundo plano
Actualización: noviembre 2007
Si tiene una operación que tarda mucho tiempo en completarse y no desea causar retrasos en la interfaz de usuario, puede utilizar la clase BackgroundWorker para ejecutar la operación en otro subproceso.
En el ejemplo de código siguiente se muestra cómo ejecutar en segundo plano una operación que exige mucho tiempo. El formulario tiene los botones Iniciar y Cancelar. Haga clic en el botón Iniciar para ejecutar una operación asincrónica. Haga clic en el botón Cancelar para detener una operación asincrónica en ejecución. El resultado de cada operación se muestra en MessageBox.
Visual Studio ofrece una amplia compatibilidad para esta tarea.
Ejemplo
Imports System
Imports System.ComponentModel
Imports System.Drawing
Imports System.Threading
Imports System.Windows.Forms
Public Class Form1
Inherits Form
Public Sub New()
InitializeComponent()
End Sub
Private Sub backgroundWorker1_DoWork( _
sender As Object, e As DoWorkEventArgs) _
Handles backgroundWorker1.DoWork
' Do not access the form's BackgroundWorker reference directly.
' Instead, use the reference provided by the sender parameter.
Dim bw As BackgroundWorker = CType( sender, BackgroundWorker )
' Extract the argument.
Dim arg As Integer = Fix(e.Argument)
' Start the time-consuming operation.
e.Result = TimeConsumingOperation(bw, arg)
' If the operation was canceled by the user,
' set the DoWorkEventArgs.Cancel property to true.
If bw.CancellationPending Then
e.Cancel = True
End If
End Sub
' This event handler demonstrates how to interpret
' the outcome of the asynchronous operation implemented
' in the DoWork event handler.
Private Sub backgroundWorker1_RunWorkerCompleted( _
sender As Object, e As RunWorkerCompletedEventArgs) _
Handles backgroundWorker1.RunWorkerCompleted
If e.Cancelled Then
' The user canceled the operation.
MessageBox.Show("Operation was canceled")
ElseIf (e.Error IsNot Nothing) Then
' There was an error during the operation.
Dim msg As String = String.Format("An error occurred: {0}", e.Error.Message)
MessageBox.Show(msg)
Else
' The operation completed normally.
Dim msg As String = String.Format("Result = {0}", e.Result)
MessageBox.Show(msg)
End If
End Sub
' This method models an operation that may take a long time
' to run. It can be cancelled, it can raise an exception,
' or it can exit normally and return a result. These outcomes
' are chosen randomly.
Private Function TimeConsumingOperation( _
bw As BackgroundWorker, _
sleepPeriod As Integer) As Integer
Dim result As Integer = 0
Dim rand As New Random()
While Not bw.CancellationPending
Dim [exit] As Boolean = False
Select Case rand.Next(3)
' Raise an exception.
Case 0
Throw New Exception("An error condition occurred.")
Exit While
' Sleep for the number of milliseconds
' specified by the sleepPeriod parameter.
Case 1
Thread.Sleep(sleepPeriod)
Exit While
' Exit and return normally.
Case 2
result = 23
[exit] = True
Exit While
Case Else
Exit While
End Select
If [exit] Then
Exit While
End If
End While
Return result
End Function
Private Sub startButton_Click(ByVal sender As Object, ByVal e As EventArgs) Handles startBtn.Click
Me.backgroundWorker1.RunWorkerAsync(2000)
End Sub
Private Sub cancelButton_Click(ByVal sender As Object, ByVal e As EventArgs) Handles cancelBtn.Click
Me.backgroundWorker1.CancelAsync()
End Sub
' <summary>
' Required designer variable.
' </summary>
Private components As System.ComponentModel.IContainer = Nothing
' <summary>
' Clean up any resources being used.
' </summary>
' <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
Protected Overrides Sub Dispose(ByVal disposing As Boolean)
If disposing AndAlso (components IsNot Nothing) Then
components.Dispose()
End If
MyBase.Dispose(disposing)
End Sub 'Dispose
#Region "Windows Form Designer generated code"
' <summary>
' Required method for Designer support - do not modify
' the contents of this method with the code editor.
' </summary>
Private Sub InitializeComponent()
Me.backgroundWorker1 = New System.ComponentModel.BackgroundWorker()
Me.startBtn = New System.Windows.Forms.Button()
Me.cancelBtn = New System.Windows.Forms.Button()
Me.SuspendLayout()
'
' backgroundWorker1
'
Me.backgroundWorker1.WorkerSupportsCancellation = True
'
' startButton
'
Me.startBtn.Location = New System.Drawing.Point(12, 12)
Me.startBtn.Name = "startButton"
Me.startBtn.Size = New System.Drawing.Size(75, 23)
Me.startBtn.TabIndex = 0
Me.startBtn.Text = "Start"
'
' cancelButton
'
Me.cancelBtn.Location = New System.Drawing.Point(94, 11)
Me.cancelBtn.Name = "cancelButton"
Me.cancelBtn.Size = New System.Drawing.Size(75, 23)
Me.cancelBtn.TabIndex = 1
Me.cancelBtn.Text = "Cancel"
'
' Form1
'
Me.AutoScaleDimensions = New System.Drawing.SizeF(6.0F, 13.0F)
Me.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font
Me.ClientSize = New System.Drawing.Size(183, 49)
Me.Controls.Add(cancelBtn)
Me.Controls.Add(startBtn)
Me.Name = "Form1"
Me.Text = "Form1"
Me.ResumeLayout(False)
End Sub
#End Region
Private WithEvents backgroundWorker1 As System.ComponentModel.BackgroundWorker
Private WithEvents startBtn As System.Windows.Forms.Button
Private WithEvents cancelBtn As System.Windows.Forms.Button
End Class
Public Class Program
Private Sub New()
End Sub
' <summary>
' The main entry point for the application.
' </summary>
<STAThread()> _
Shared Sub Main()
Application.EnableVisualStyles()
Application.Run(New Form1())
End Sub
End Class
using System;
using System.ComponentModel;
using System.Drawing;
using System.Threading;
using System.Windows.Forms;
namespace BackgroundWorkerExample
{
public class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
// Do not access the form's BackgroundWorker reference directly.
// Instead, use the reference provided by the sender parameter.
BackgroundWorker bw = sender as BackgroundWorker;
// Extract the argument.
int arg = (int)e.Argument;
// Start the time-consuming operation.
e.Result = TimeConsumingOperation(bw, arg);
// If the operation was canceled by the user,
// set the DoWorkEventArgs.Cancel property to true.
if (bw.CancellationPending)
{
e.Cancel = true;
}
}
// This event handler demonstrates how to interpret
// the outcome of the asynchronous operation implemented
// in the DoWork event handler.
private void backgroundWorker1_RunWorkerCompleted(
object sender,
RunWorkerCompletedEventArgs e)
{
if (e.Cancelled)
{
// The user canceled the operation.
MessageBox.Show("Operation was canceled");
}
else if (e.Error != null)
{
// There was an error during the operation.
string msg = String.Format("An error occurred: {0}", e.Error.Message);
MessageBox.Show(msg);
}
else
{
// The operation completed normally.
string msg = String.Format("Result = {0}", e.Result);
MessageBox.Show(msg);
}
}
// This method models an operation that may take a long time
// to run. It can be cancelled, it can raise an exception,
// or it can exit normally and return a result. These outcomes
// are chosen randomly.
private int TimeConsumingOperation(
BackgroundWorker bw,
int sleepPeriod )
{
int result = 0;
Random rand = new Random();
while (!bw.CancellationPending)
{
bool exit = false;
switch (rand.Next(3))
{
// Raise an exception.
case 0:
{
throw new Exception("An error condition occurred.");
break;
}
// Sleep for the number of milliseconds
// specified by the sleepPeriod parameter.
case 1:
{
Thread.Sleep(sleepPeriod);
break;
}
// Exit and return normally.
case 2:
{
result = 23;
exit = true;
break;
}
default:
{
break;
}
}
if( exit )
{
break;
}
}
return result;
}
private void startBtn_Click(object sender, EventArgs e)
{
this.backgroundWorker1.RunWorkerAsync(2000);
}
private void cancelBtn_Click(object sender, EventArgs e)
{
this.backgroundWorker1.CancelAsync();
}
/// <summary>
/// Required designer variable.
/// </summary>
private System.ComponentModel.IContainer components = null;
/// <summary>
/// Clean up any resources being used.
/// </summary>
/// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
protected override void Dispose(bool disposing)
{
if (disposing && (components != null))
{
components.Dispose();
}
base.Dispose(disposing);
}
#region Windows Form Designer generated code
/// <summary>
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
/// </summary>
private void InitializeComponent()
{
this.backgroundWorker1 = new System.ComponentModel.BackgroundWorker();
this.startBtn = new System.Windows.Forms.Button();
this.cancelBtn = new System.Windows.Forms.Button();
this.SuspendLayout();
//
// backgroundWorker1
//
this.backgroundWorker1.WorkerSupportsCancellation = true;
this.backgroundWorker1.DoWork += new System.ComponentModel.DoWorkEventHandler(this.backgroundWorker1_DoWork);
this.backgroundWorker1.RunWorkerCompleted += new System.ComponentModel.RunWorkerCompletedEventHandler(this.backgroundWorker1_RunWorkerCompleted);
//
// startBtn
//
this.startBtn.Location = new System.Drawing.Point(12, 12);
this.startBtn.Name = "startBtn";
this.startBtn.Size = new System.Drawing.Size(75, 23);
this.startBtn.TabIndex = 0;
this.startBtn.Text = "Start";
this.startBtn.Click += new System.EventHandler(this.startBtn_Click);
//
// cancelBtn
//
this.cancelBtn.Location = new System.Drawing.Point(94, 11);
this.cancelBtn.Name = "cancelBtn";
this.cancelBtn.Size = new System.Drawing.Size(75, 23);
this.cancelBtn.TabIndex = 1;
this.cancelBtn.Text = "Cancel";
this.cancelBtn.Click += new System.EventHandler(this.cancelBtn_Click);
//
// Form1
//
this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
this.ClientSize = new System.Drawing.Size(183, 49);
this.Controls.Add(this.cancelBtn);
this.Controls.Add(this.startBtn);
this.Name = "Form1";
this.Text = "Form1";
this.ResumeLayout(false);
}
#endregion
private System.ComponentModel.BackgroundWorker backgroundWorker1;
private System.Windows.Forms.Button startBtn;
private System.Windows.Forms.Button cancelBtn;
}
public class Program
{
private Program()
{
}
/// <summary>
/// The main entry point for the application.
/// </summary>
[STAThread]
static void Main()
{
Application.EnableVisualStyles();
Application.Run(new Form1());
}
}
}
Compilar el código
Este ejemplo requiere:
- Referencias a los ensamblados System, System.Drawing y System.Windows.Forms.
Para obtener información sobre la generación de este ejemplo desde la línea de comandos de Visual Basic o Visual C#, vea Generar desde la línea de comandos (Visual Basic) o Generar la línea de comandos con csc.exe. También puede generar este ejemplo en Visual Studio pegando el código en un proyecto nuevo.
Vea también
Tareas
Cómo: Implementar un formulario que utiliza una operación en segundo plano