将参数传递给backgroundWorker(用作取消按钮)

本文关键字：取消 按钮 参数传递 backgroundWorker | 更新日期: 2023-09-27 18:15:06

我是c#和面向对象编程的新手。我一直在尝试在我的GUI中实现一个"取消"按钮，以便用户可以在过程中停止它。

我读到这个问题:如何实现停止/取消按钮?并确定backgroundWorker对我来说应该是一个很好的选择，但是给出的示例并没有解释如何将参数传递给backgroundWorker。

我的问题是，我不知道如何传递一个参数到backgroundWorker，这样它就会停止进程;我只能让backgroundWorker停止自己。

我创建了以下代码来尝试学习这一点，我的表单有两个按钮(buttonStart和buttonStop)和一个backgroundWorker (backgroundWorkerStopCheck):

using System;
using System.ComponentModel;
using System.Windows.Forms;
using System.Threading;
using System.Timers;
namespace TestBackgroundWorker
{
    public partial class Form1 : Form
    {
        public Form1()
        {         
            InitializeComponent();
            // Set the background worker to allow the user to stop the process. 
            backgroundWorkerStopCheck.WorkerSupportsCancellation = true;
        }
        private System.Timers.Timer myTimer;
        private void backgroundWorkerStopCheck_DoWork(object sender, DoWorkEventArgs e)
        {
            //If cancellation is pending, cancel work.  
            if (backgroundWorkerStopCheck.CancellationPending)
            {
                e.Cancel = true;
                return;
            }
        }
        private void buttonStart_Click(object sender, EventArgs e)
        {
            // Notify the backgroundWorker that the process is starting.
            backgroundWorkerStopCheck.RunWorkerAsync();
            LaunchCode();
        }
        private void buttonStop_Click(object sender, EventArgs e)
        {
            // Tell the backgroundWorker to stop process.
            backgroundWorkerStopCheck.CancelAsync();
        }
        private void LaunchCode()
        {
            buttonStart.Enabled = false; // Disable the start button to show that the process is ongoing.
            myTimer = new System.Timers.Timer(5000); // Waste five seconds.
            myTimer.Elapsed += new ElapsedEventHandler(myTimer_Elapsed);
            myTimer.Enabled = true; // Start the timer.
        }
        void myTimer_Elapsed(object sender, ElapsedEventArgs e)
        {
            buttonStart.Enabled = true; // ReEnable the Start button to show that the process either finished or was cancelled.
        }
    }
}

代码，如果工作正常的话，在用户点击"开始"按钮之前，会在那里停留5秒钟，或者在用户点击"停止"按钮时，会迅速重新激活"开始"按钮。

这段代码有两个问题，我不确定如何处理:

1)"myTimer_Elapsed"方法在尝试启用Start按钮时导致InvalidOperationException，因为"跨线程操作无效"。如何避免跨线程操作?

2)现在backgroundWorker没有完成任何事情，因为我不知道如何为它提供参数，这样，当它被取消时，它将停止计时器。

我很感激任何帮助!

将参数传递给backgroundWorker(用作取消按钮)

首先，避免"跨线程操作无效"的问题是在控件上使用Invoke。您不能使用来自其他线程的控件。

关于第二个问题，我将以如下方式实现。这是一个支持取消的最小后台worker实现。

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
namespace WindowsFormsApplication5
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            // Set the background worker to allow the user to stop the process. 
            backgroundWorkerStopCheck.WorkerSupportsCancellation = true;
            backgroundWorkerStopCheck.DoWork += new DoWorkEventHandler(backgroundWorkerStopCheck_DoWork);
        }
        private void backgroundWorkerStopCheck_DoWork(object sender, DoWorkEventArgs e)
        {
            try
            {
                for (int i = 0; i < 50; i++)
                {
                    if (backgroundWorkerStopCheck.CancellationPending)
                    {
                        // user cancel request
                        e.Cancel = true;
                        return;
                    }
                    System.Threading.Thread.Sleep(100);
                }
            }
            finally
            {
                InvokeEnableStartButton();
            }
        }
        private void buttonStart_Click(object sender, EventArgs e)
        {
            //disable start button before launch work
            buttonStart.Enabled = false;
            // start worker
            backgroundWorkerStopCheck.RunWorkerAsync();
        }
        private void buttonStop_Click(object sender, EventArgs e)
        {
            // Tell the backgroundWorker to stop process.
            backgroundWorkerStopCheck.CancelAsync();
        }
        private void InvokeEnableStartButton()
        {
            // this method is called from a thread,
            // we need to Invoke to avoid "cross thread exception"
            if (this.InvokeRequired)
            {
                this.Invoke(new EnableStartButtonDelegate(EnableStartButton));
            }
            else
            {
                EnableStartButton();
            }
        }
        private void EnableStartButton()
        {
            buttonStart.Enabled = true;
        }
    }
    internal delegate void EnableStartButtonDelegate();
}

关于向worker传递参数，您可以在RunWorkerAsync()方法中传递任何对象，并在backgroundWorkerStopCheck_DoWork方法中接收:

  ...
  backgroundWorkerStopCheck.RunWorkerAsync("hello");
  ...
  private void backgroundWorkerStopCheck_DoWork(object sender, DoWorkEventArgs e)
  {
      string argument = e.Argument as string;
      // argument value is "hello"
      ...
  }

希望能有所帮助。

试试这个例子，你会看到如何从BackgroundWorker传入和传入数据:

public partial class Form1 : Form
{
    BackgroundWorker bw = new BackgroundWorker();
    public Form1()
    {
        InitializeComponent();
        bw.DoWork += new DoWorkEventHandler(bw_DoWork);
        bw.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bw_RunWorkerCompleted);
        bw.WorkerSupportsCancellation = true;
    }
    private void button1_Click(object sender, EventArgs e)
    {
        btnStart.Enabled = false;
        btnCancel.Enabled = true;
        double[] data = new double[1000000];
        Random r = new Random();
        for (int i = 0; i < data.Length; i++)
            data[i] = r.NextDouble();
        bw.RunWorkerAsync(data);
    }
    void bw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
    {
        btnStart.Enabled = true;
        btnCancel.Enabled = false;
        if (!e.Cancelled)
        {
            double result = (double)e.Result;
            MessageBox.Show(result.ToString());
        }
    }
    void bw_DoWork(object sender, DoWorkEventArgs e)
    {
        double[] data = (double[])e.Argument;
        for (int j = 0; j < 200; j++)
        {
            double result = 0;
            for (int i = 0; i < data.Length; i++)
            {
                if (bw.CancellationPending)
                {
                    e.Cancel = true;
                    return;
                }
                result += data[i];
            }
            e.Result = result;
        }
    }
    private void btnCancel_Click(object sender, EventArgs e)
    {
        bw.CancelAsync();
        btnStart.Enabled = true;
        btnCancel.Enabled = false;
    }
}
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