Comment : exécuter une opération en arrière-plan
Si vous avez une opération dont l'exécution va prendre beaucoup de temps et que vous ne souhaitez pas causer de retards dans votre interface utilisateur, vous pouvez utiliser la classe BackgroundWorker pour exécuter l'opération sur un autre thread.
L'exemple de code suivant indique comment exécuter en arrière-plan une opération qui prend du temps. Le formulaire possède des boutons Démarrer et Annuler. Cliquez sur le bouton Démarrer pour exécuter une opération asynchrone. Cliquez sur le bouton Annuler pour exécuter une opération asynchrone. Le résultat de chaque opération est affiché dans un MessageBox.
Il existe une prise en charge étendue pour cette tâche dans Visual Studio.
Pour plus d'informations, consultez Procédure pas à pas : exécution d'une opération en arrière-plan et Procédure pas à pas : exécution d'une opération en arrière-plan et Procédure pas à pas : exécution d'une opération en arrière-plan et Procédure pas à pas : exécution d'une opération en arrière-plan.
Exemple
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());
}
}
}
Compilation du code
Cet exemple nécessite les actions ou les éléments suivants :
- Références aux assemblys System, System.Drawing et System.Windows.Forms.
Pour plus d'informations sur la génération de cet exemple à partir de la ligne de commande pour Visual Basic ou Visual C#, consultez Génération à partir de la ligne de commande (Visual Basic) ou Génération à partir de la ligne de commande avec csc.exe. Vous pouvez aussi générer cet exemple dans Visual Studio en collant le code dans un nouveau projet. Pour plus d'informations, consultez Comment : compiler et exécuter un exemple complet de code Windows Forms à l'aide de Visual Studio et Comment : compiler et exécuter un exemple complet de code Windows Forms à l'aide de Visual Studio et Comment : compiler et exécuter un exemple complet de code Windows Forms à l'aide de Visual Studio et Comment : compiler et exécuter un exemple complet de code Windows Forms à l'aide de Visual Studio et Comment : compiler et exécuter un exemple complet de code Windows Forms à l'aide de Visual Studio.
Voir aussi
Tâches
Comment : implémenter un formulaire qui utilise une opération d'arrière-plan