如何实现停止/取消按钮
本文关键字:取消 按钮 何实现 实现 | 更新日期: 2023-09-27 18:08:49
我有一个processData()方法,它接受大量数据并对其进行一些处理。有一个启动处理的开始按钮。我需要一个取消按钮,可以在任何地方停止处理。我该如何实现呢?我不明白的是,一旦处理开始,如何使取消按钮可用,因为当函数运行时,UI的其余部分被冻结。
BackgroundWorker。CancelAsync方法就是你需要的。这是一个很好的例子。
如果你有一个耗时的进程,你将不得不使用一个单独的线程来处理它,以支持取消。如果你在主线程(UI线程)中执行那个耗时的进程,它将会很忙,直到它完成那个任务才会考虑你的取消请求。这就是为什么你会遇到UI冻结。
如果你使用backgroundWorker来完成耗时的任务,如果你在backgroundWorker中检查了CancellationPending标志。DoWork方法可以实现你想要的。
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();
}
}
}
使用BackgroundWorker
将重代码放在DoWork
事件中
取消按钮应调用BackgroundWorker
上的CancelAsync
。
在DoWork
中的健康代码中,定期检查CancellationPending
属性。如果属性为true
,则应中止该工作。
在
处停止处理
如果你的意思是进程应该立即停止,而不是等待它检查取消令牌的时刻,你可以考虑在一个单独的AppDomain中运行进程,并在取消时杀死它。
虽然这是完全可能的,但我建议像其他答案一样控制终止,特别是当您的流程改变外部状态时。