Question

我有一个方法processData（），它接收大量数据并对其进行一些处理。有一个启动按钮启动处理。我需要一个取消按钮，无论它在哪里都停止处理。我怎么能实现这样的东西？我没有得到的是如何在处理开始后使取消按钮可用，因为当函数运行时，其余的UI被冻结。

Answer 1

BackgroundWorker.CancelAsync方法就是您所需要的。 Here就是一个很好的例子。

如果你有一个耗时的过程，你将不得不使用一个单独的线程来处理它，以支持取消。如果您在主线程（UI线程）中执行该耗时过程，它将很忙，并且在完成该任务之前不会将您的取消请求记入帐户。这就是你遇到UI冻结的原因。

如果您使用backgroundWorker执行耗时的任务，并且在BackgroundWorker.DoWork方法中检查CancellationPending标志，则可以实现您想要的效果。

using System;  
using System.Collections.Generic;  
using System.ComponentModel;  
using System.Data;  
using System.Drawing;  
using System.Text;  
using System.Windows.Forms;  

namespace BackgroundWorker  
{  
    public partial class Form1 : Form  
    {  
        public Form1()  
        {  
            InitializeComponent();  

            //mandatory. Otherwise will throw an exception when calling ReportProgress method  
            backgroundWorker1.WorkerReportsProgress = true;   

            //mandatory. Otherwise we would get an InvalidOperationException when trying to cancel the operation  
            backgroundWorker1.WorkerSupportsCancellation = true;  
        }  

        //This method is executed in a separate thread created by the background worker.  
        //so don't try to access any UI controls here!! (unless you use a delegate to do it)  
        //this attribute will prevent the debugger to stop here if any exception is raised.  
        //[System.Diagnostics.DebuggerNonUserCodeAttribute()]  
        private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)  
        {  
            //NOTE: we shouldn't use a try catch block here (unless you rethrow the exception)  
            //the backgroundworker will be able to detect any exception on this code.  
            //if any exception is produced, it will be available to you on   
            //the RunWorkerCompletedEventArgs object, method backgroundWorker1_RunWorkerCompleted  
            //try  
            //{  
                DateTime start = DateTime.Now;  
                e.Result = "";  
                for (int i = 0; i < 100; i++)  
                {  
                    System.Threading.Thread.Sleep(50); //do some intense task here.  
                    backgroundWorker1.ReportProgress(i, DateTime.Now); //notify progress to main thread. We also pass time information in UserState to cover this property in the example.  
                    //Error handling: uncomment this code if you want to test how an exception is handled by the background worker.  
                    //also uncomment the mentioned attribute above to it doesn't stop in the debugger.  
                    //if (i == 34)  
                    //    throw new Exception("something wrong here!!");  

                    //if cancellation is pending, cancel work.  
                    if (backgroundWorker1.CancellationPending)  
                    {  
                        e.Cancel = true;   
                        return;  
                    }  
                }  

                TimeSpan duration = DateTime.Now - start;  

                //we could return some useful information here, like calculation output, number of items affected, etc.. to the main thread.  
                e.Result = "Duration: " + duration.TotalMilliseconds.ToString() + " ms.";  
            //}  
            //catch(Exception ex){  
            //    MessageBox.Show("Don't use try catch here, let the backgroundworker handle it for you!");  
            //}  
        }  

        //This event is raised on the main thread.  
        //It is safe to access UI controls here.  
        private void backgroundWorker1_ProgressChanged(object sender,   
            ProgressChangedEventArgs e)  
        {  
            progressBar1.Value = e.ProgressPercentage; //update progress bar  

            DateTime time = Convert.ToDateTime(e.UserState); //get additional information about progress  

            //in this example, we log that optional additional info to textbox  
            txtOutput.AppendText(time.ToLongTimeString());  
            txtOutput.AppendText(Environment.NewLine);              
        }  

        //This is executed after the task is complete whatever the task has completed: a) sucessfully, b) with error c)has been cancelled  
        private void backgroundWorker1_RunWorkerCompleted(object sender,   
            RunWorkerCompletedEventArgs e)  
        {  
            if (e.Cancelled) {  
                MessageBox.Show("The task has been cancelled");  
            }  
            else if (e.Error != null)  
            {                  
                MessageBox.Show("Error. Details: " + (e.Error as Exception).ToString());  
            }  
            else {  
                MessageBox.Show("The task has been completed. Results: " + e.Result.ToString());  
            }  

        }  

        private void btoCancel_Click(object sender, EventArgs e)  
        {  
            //notify background worker we want to cancel the operation.  
            //this code doesn't actually cancel or kill the thread that is executing the job.  
            backgroundWorker1.CancelAsync();  
        }  

        private void btoStart_Click(object sender, EventArgs e)  
        {  
            backgroundWorker1.RunWorkerAsync();  
        }  
    }  
}

Answer 2

使用BackgroundWorker。

将重要代码放入DoWork事件。

取消按钮应拨打CancelAsync上的BackgroundWorker。

在DoWork中的heacy代码中，定期检查CancellationPending属性。如果属性为true，您应该中止工作。

Answer 3

停止处理
处的处理

如果您的意思是流程应立即停止，甚至不等待检查取消令牌的时刻，您可以考虑在separate AppDomain中运行该流程并在取消时将其终止。

虽然这是完全可能的，但我会建议在其他答案中进行受控终止，特别是当您的过程改变外部状态时。

如何实现停止/取消按钮？

3 个答案: