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BackgroundWorker クラス

メモ : このクラスは、.NET Framework version 2.0 で新しく追加されたものです。

個別のスレッドで操作を実行します。

名前空間: System.ComponentModel
アセンブリ: System (system.dll 内)

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

BackgroundWorker クラスを使用すると、個別の専用スレッドで操作を実行できます。ダウンロードやデータベース トランザクションのように時間を要する操作によって、操作の実行中にユーザー インターフェイス (UI: User Interface) が応答しなくなったように思われる場合があります。UI にすぐに応答させたいときに、このような操作に関連する長時間の遅延が発生している場合は、BackgroundWorker クラスに便利な解決方法が用意されています。

時間を要する操作をバックグラウンドで実行するには、BackgroundWorker を作成し、操作の進行状況を報告したり、操作の終了時に通知したりするイベントを待機します。BackgroundWorker は、プログラムによって作成することも、ツールボックスの [コンポーネント] タブからオブジェクトをフォームにドラッグすることもできます。Windows フォーム デザイナで BackgroundWorker を作成すると、オブジェクトは [コンポーネント トレイ] に表示され、そのプロパティは [プロパティ] ウィンドウに表示されます。

バックグラウンド操作を設定するには、DoWork イベントのイベント ハンドラを追加します。このイベント ハンドラで、時間を要する操作を呼び出します。操作を開始するには、RunWorkerAsync を呼び出します。進行状況の更新の通知を受け取るには、ProgressChanged イベントを処理します。操作の完了時に通知を受け取るには、RunWorkerCompleted イベントを処理します。

メモメモ

DoWork イベント ハンドラでユーザー インターフェイス オブジェクトを操作しないように注意する必要があります。代わりに、ProgressChanged イベントと RunWorkerCompleted イベントを通じてユーザー インターフェイスと通信します。

BackgroundWorker イベントは、AppDomain の境界を越えてマーシャリングされません。BackgroundWorker コンポーネントを、複数の AppDomain でのマルチスレッド操作を実行するために使用しないでください。

バックグラウンド操作にパラメータが必要な場合は、使用するパラメータを指定して RunWorkerAsync を呼び出します。DoWork イベント ハンドラの内部では、DoWorkEventArgs.Argument プロパティからパラメータを抽出できます。

BackgroundWorker の詳細については、「方法 : バックグラウンドで操作を実行する」を参照してください。

メモメモ

このクラスに適用される HostProtectionAttribute 属性の Resources プロパティの値は、SharedState です。HostProtectionAttribute は、デスクトップ アプリケーション (一般的には、アイコンをダブルクリック、コマンドを入力、またはブラウザに URL を入力して起動するアプリケーション) には影響しません。詳細については、HostProtectionAttribute クラスのトピックまたは「SQL Server プログラミングとホスト保護属性」を参照してください。

時間を要する操作を非同期で実行するための BackgroundWorker クラスの使用方法を次のコード例に示します。この演算では、選択されたフィボナッチ数の計算、計算の進行に伴う進行状況の更新の報告、および保留中の計算のキャンセルの許可を行います。

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

この型の public static (Visual Basic では Shared) メンバはすべて、スレッド セーフです。インスタンス メンバの場合は、スレッド セーフであるとは限りません。

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

開発プラットフォームの中には、.NET Framework によってサポートされていないバージョンがあります。サポートされているバージョンについては、「システム要件」を参照してください。

.NET Framework

サポート対象 : 2.0
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