c# - 取消异步任务

Question

例如我有这样的东西。当我单击第一个按钮时，它会启动异步进程，然后我单击第二个按钮，它会启动第二个进程。但是我只需要一个进程在点击每个按钮后就可以工作。如何取消其他进程？

namespace WpfApplication55
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        TestCombo TC = new TestCombo();
        public MainWindow()
        {
            DataContext = TC;
            InitializeComponent();
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            TC.Begin(60);
        }

        private void Button_Click1(object sender, RoutedEventArgs e)
        {
            TC.Begin(120);
        }
    }

    public class TestCombo:INotifyPropertyChanged
    {
        private int someData;
        public int SomeData 
        {
            get { return someData; }
            set { someData = value; RaisePropertyChanged("SomeData"); }
        }

        public void StartCount(int input)
        {
            SomeData = input;
            while (input>0)
            {
                System.Threading.Thread.Sleep(1000);
                input -= 1;
                SomeData = input;
            }
        }

        public void Begin(int input)
        {   
            Action<int> Start = new Action<int>(StartCount);
            IAsyncResult result = Start.BeginInvoke(input, null, null);
        }

        public event PropertyChangedEventHandler PropertyChanged;

        private void RaisePropertyChanged (string info)
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(info));
        }
    }
}

Answer 1

我不太确定您希望 StartCount 中的 while 条件如何工作，但只要您评估新的 CancellationToken，您应该可以取消。请记住 Thread.Sleep 在休眠时不会取消。所以你可能会有最多 1 秒的延迟。

public void StartCount(int input, CancellationToken token)
{
    SomeData = input;
    while (input > 0 && !token.IsCancellationRequested)
    {
        System.Threading.Thread.Sleep(1000);
        input -= 1;
        SomeData = input;
    }
}

IAsyncResult process;
public void Begin(int input)
{
    if (process != null && !process.IsCompleted)
        ((CancellationTokenSource)process.AsyncState).Cancel();
    Action<int, CancellationToken> Start = new Action<int, CancellationToken>(StartCount);
    var cancelSource = new CancellationTokenSource();
    process = Start.BeginInvoke(input,cancelSource.Token, null, cancelSource);
}