Gewusst wie: Ausführen eines Vorgangs im HintergrundHow to: Run an Operation in the Background

Gibt es einen Vorgang, der bis zu seinem Abschluss eine lange Zeit in Anspruch nimmt, und Sie möchten keine Verzögerungen in der Benutzeroberfläche verursachen, können Sie die BackgroundWorker-Klasse dazu verwenden, den Vorgang über einen anderen Thread auszuführen.If you have an operation that will take a long time to complete, and you do not want to cause delays in your user interface, you can use the BackgroundWorker class to run the operation on another thread.

Im folgenden Codebeispiel wird gezeigt, wie ein zeitaufwändiger Vorgang im Hintergrund ausgeführt wird.The following code example shows how to run a time-consuming operation in the background. Das Formular verfügt über die Schaltflächen Start und Abbrechen.The form has Start and Cancel buttons. Klicken Sie auf die Schaltfläche Start, um einen asynchronen Vorgang auszuführen.Click the Start button to run an asynchronous operation. Klicken Sie auf die Schaltfläche Abbrechen, um einen aktiven asynchronen Vorgang anzuhalten.Click the Cancel button to stop a running asynchronous operation. Das Ergebnis jedes Vorgangs wird in einem MessageBox-Steuerelement angezeigt.The outcome of each operation is displayed in a MessageBox.

Visual Studio bietet umfassende Unterstützung für diese Aufgabe.There is extensive support for this task in Visual Studio.

Siehe auch Exemplarische Vorgehensweise: Ausführen eines Vorgangs im Hintergrund.Also see Walkthrough: Running an Operation in the Background.

BeispielExample

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());
        }
    }
}
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

    ' Required designer variable.
    Private components As System.ComponentModel.IContainer = Nothing


    ' Clean up any resources being used.
    ' <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"


    ' Required method for Designer support - do not modify
    ' the contents of this method with the code editor.
    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

    ' The main entry point for the application.
    <STAThread()> _
    Shared Sub Main()
        Application.EnableVisualStyles()
        Application.Run(New Form1())
    End Sub


End Class

Kompilieren des CodesCompiling the Code

Für dieses Beispiel benötigen Sie Folgendes:This example requires:

  • Verweise auf die Assemblys "System", "System.Drawing" und "System.Windows.Forms".References to the System, System.Drawing and System.Windows.Forms assemblies.

Informationen zum Erstellen dieses Beispiels über die Befehlszeile für Visual Basic oder Visual c# finden Sie unter erstellen über die Befehlszeile oder Befehlszeile mit csc.exe.For information about building this example from the command line for Visual Basic or Visual C#, see Building from the Command Line or Command-line Building With csc.exe. Sie können auch in diesem Beispiel in Visual Studio erstellen, indem Sie den Code in ein neues Projekt einfügen.You can also build this example in Visual Studio by pasting the code into a new project. Siehe auch Gewusst wie: Kompilieren und Ausführen eines vollständigen Windows Forms-Codebeispiels mit Visual Studio.Also see How to: Compile and Run a Complete Windows Forms Code Example Using Visual Studio.

Siehe auchSee Also

BackgroundWorker
DoWorkEventArgs
Vorgehensweise: Implementieren eines Formulars, das eine Hintergrundoperation verwendetHow to: Implement a Form That Uses a Background Operation
BackgroundWorker-KomponenteBackgroundWorker Component