应用程序停用时BackgroundWorker线程的接近程度如何？

Question

我创建线程BackgroundWorker,并在循环中我每次检查是否CancellationPending为真,如下所示:

   public MainPage()
    {
        InitializeComponent();

        bw = new BackgroundWorker();
        bw.WorkerReportsProgress = true;
        bw.WorkerSupportsCancellation = true;
        bw.DoWork += new DoWorkEventHandler(bw_DoWork);
        bw.ProgressChanged += new ProgressChangedEventHandler(bw_ProgressChanged);
        bw.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bw_RunWorkerCompleted);
    }

    private void ButtonStart_Click(object sender, RoutedEventArgs e)
    {
        if (bw.IsBusy != true)
        {
            bw.RunWorkerAsync();
        }
    }

    private void ButtonCancel_Click(object sender, RoutedEventArgs e)
    {
        if (bw.WorkerSupportsCancellation)
        {
            bw.CancelAsync();
        }
    }

    private void bw_DoWork(object sender, DoWorkEventArgs e)
    {
        BackgroundWorker worker = sender as BackgroundWorker;

        for (int i = 1; i <= 100; i++)
        {
            Debug.WriteLine("The tread is working");
            if (worker.CancellationPending)
            {
                e.Cancel = true;
                bw.CancelAsync();
                break;
            }
            else
            {

                System.Threading.Thread.Sleep(500);
                worker.ReportProgress(i);
            }
        }
    }

    private void bw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
    {
        if (e.Cancelled)
        {
            tbProgress.Text = "Canceled";
        }
        else if (e.Error != null)
        {
            tbProgress.Text = "Error: " + e.Error.Message;
        }
        else
        {
            tbProgress.Text = "Done";
        } 
    }

    private void bw_ProgressChanged(object sender, ProgressChangedEventArgs e)
    {
        tbProgress.Text = e.ProgressPercentage.ToString() + "%";
    }

当应用程序停用时,线程未关闭,它被中止并发生异常.BackgroundWorker应用程序停用时与线程的接近程度如何？

Answer 1

当一个应用程序被停用时,除了主UI线程之外的每个线程一旦变为活动状态就会抛出一个ThreadAbortException.这似乎是"按设计"作为一种迫使应用程序快速停止他们正在做的事情的方式.线程可以捕获ThreadAbortException并包装它们正在做的事情,但要注意ThreadAbortException将在catch块的末尾再次自动引发.finally块中的任何代码也将被执行.

对于您的特定问题,在应用程序停用时没有理由尝试取消BackgroundWorker,因为ThreadAbortException将发生并将有效地停止后台工作程序.如果你想在发生这种情况时做一些事情来清理,你可以在bw_DoWork中捕获ThreadAbortException,做你需要做的事情,然后让它死掉.

要在激活后重新启动它,您必须重新启动后台工作程序,就像第一次运行应用程序时一样.

Answer 2

你设置BackgroundWorker为可取消吗？

 var bg= new BackgroundWorker();
 bg.WorkerSupportsCancellation = true;

从文档:

WorkerSupportsCancellation如果希望BackgroundWorker支持取消,请将该属性设置为true.如果此属性为true,则可以调用该CancelAsync方法来中断后台操作.

你的代码似乎也错了,你应该调用CancelAsync()线程代码的外部,这将设置CancellationPending你可以用来退出循环的标志.

虽然我不是100%肯定,因为我不知道bw变量来自哪里.`