Gewusst wie: Ausführen eines Vorgangs im Hintergrund
Wenn die Ausführung eines Vorgangs sehr lange dauert und Sie Verzögerungen in der Benutzeroberfläche vermeiden möchten, können Sie den Vorgang mithilfe der BackgroundWorker-Klasse in einem anderen Thread ausführen.
Im folgenden Codebeispiel wird gezeigt, wie eine zeitaufwändige Operation im Hintergrund ausgeführt wird. Das Formular verfügt über die Schaltflächen Start und Abbrechen. Klicken Sie auf die Schaltfläche Start, um eine asynchrone Operation auszuführen. Klicken Sie auf die Schaltfläche Abbrechen, um eine laufende asynchrone Operation anzuhalten. Das Ergebnis jeder Operation wird in einer MessageBox angezeigt.
Visual Studio bietet umfassende Unterstützung für diese Aufgabe.
Weitere Informationen finden Sie unter Exemplarische Vorgehensweise: Ausführen eines Vorgangs im Hintergrund und Exemplarische Vorgehensweise: Ausführen eines Vorgangs im Hintergrund und Exemplarische Vorgehensweise: Ausführen eines Vorgangs im Hintergrund und Exemplarische Vorgehensweise: Ausführen eines Vorgangs im Hintergrund.
Beispiel
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());
}
}
}
Kompilieren des Codes
Für dieses Beispiel sind erforderlich:
- Verweise auf die Assemblys System, System.Drawing und System.Windows.Forms.
Informationen zum Erstellen dieses Beispiels über die Befehlszeile für Visual Basic oder Visual C# finden Sie unter Erstellen von der Befehlszeile aus (Visual Basic) oder unter Erstellen über die Befehlszeile mit csc.exe. Sie können dieses Beispiel auch in Visual Studio erstellen, indem Sie den Code in ein neues Projekt einfügen. Weitere Informationen finden Sie unter Gewusst wie: Kompilieren und Ausführen eines vollständigen Windows Forms-Codebeispiels mit Visual Studio und Gewusst wie: Kompilieren und Ausführen eines vollständigen Windows Forms-Codebeispiels mit Visual Studio und Gewusst wie: Kompilieren und Ausführen eines vollständigen Windows Forms-Codebeispiels mit Visual Studio und Gewusst wie: Kompilieren und Ausführen eines vollständigen Windows Forms-Codebeispiels mit Visual Studio und Gewusst wie: Kompilieren und Ausführen eines vollständigen Windows Forms-Codebeispiels mit Visual Studio.
Siehe auch
Aufgaben
Gewusst wie: Implementieren eines Formulars, das eine Hintergrundoperation verwendet