CancellationTokenSource不取消任务

Question

我有两个按钮用于场景，其中一个启动任务，另一个停止该任务。

   // this is the property which is used to cancel the task
   CancellationTokenSource cTokenSource;

private async void OnReadCommand()
{
   cTokenSource = new CancellationTokenSource();
   ReadAction();
}


private async void ReadAction()
{
   Task.Factory.StartNew(() => {
       while (true)
       {
           Task.Delay(TimeSpan.FromSeconds(2)).Wait();
        //writing in debug console
           Debug.WriteLine($"Some Random Nos : {Guid.NewGuid().ToString()}");
        //sending it to the ui for testing
           uiContext.Send(x => MessageArea2Content.Message = Guid.NewGuid().ToString(), null);
       }
   },cTokenSource.Token);
}
       
private async void OnCancelCommand()
{
   // it's used to cancel the task
   cTokenSource.Cancel();
}

我的应用程序是wpf和使用mvvm模式和棱镜库。在调用OnCancelCommand时，任务正在后台运行并打印GUID。我只能在OnCancelCommand上取消这项任务。

Answer 1

您需要自己实现退出循环的代码：

private async void ReadAction()
{
    Task.Factory.StartNew(() => {
        while (true)
        {
            Task.Delay(TimeSpan.FromSeconds(2)).Wait();
            //writing in debug console
            Debug.WriteLine($"Some Random Nos : {Guid.NewGuid().ToString()}");
            //sending it to the ui for testing
            uiContext.Send(x => MessageArea2Content.Message = Guid.NewGuid().ToString(), null);
            
            cTokenSource.Token.ThrowIfCancellationRequested();
        }
    },cTokenSource.Token);
}

或

private async void ReadAction()
{
    Task.Factory.StartNew(() => {
        while (true)
        {
            Task.Delay(TimeSpan.FromSeconds(2)).Wait();
            //writing in debug console
            Debug.WriteLine($"Some Random Nos : {Guid.NewGuid().ToString()}");
            //sending it to the ui for testing
            uiContext.Send(x => MessageArea2Content.Message = Guid.NewGuid().ToString(), null);
            
            if (cTokenSource.Token.IsCancellationRequested)
            {
                break; // or return;
            }
        }
    },cTokenSource.Token);

您可以在文档化任务类中找到使用示例。将CancellationToken传递给StartNew方法的唯一好处是，如果源在任务启动前被取消，它可以自动取消任务。但是，要在运行期间取消它，您需要自己编写逻辑代码。这是关于那个https://stackoverflow.com/questions/48312544/whats-the-benefit-of-passing-a-cancellationtoken-as-a-parameter-to-task-run#:~:text=In%20summary%2C%20providing%20the%20cancellation,to%20start%20running%20the%20task的另一个很好的阅读。

此外，我建议您在StartNew中执行的逻辑中使用await，这样您就不会失去异步的好处：

private async void ReadAction()
{
    Task.Factory.StartNew(async () => {
        while (true)
        {
            await Task.Delay(TimeSpan.FromSeconds(2));
            //writing in debug console
            Debug.WriteLine($"Some Random Nos : {Guid.NewGuid().ToString()}");
            //sending it to the ui for testing
            uiContext.Send(x => MessageArea2Content.Message = Guid.NewGuid().ToString(), null);
            
            if (cTokenSource.Token.IsCancellationRequested)
            {
                break; // or return;
            }
        }
    },cTokenSource.Token)

这样，线程将不再被阻塞，并将在呼叫延迟期间释放。