在BackgroundWorker中：即使出现错误，RunWorkerCompleted的e.Error == null

Question

当我把try catch块放在我执行任务的时候。在RunWorkerCompleted（）方法中，e.error使用为null。当我删除try catch块然后在RunWorkerCompleted（）方法中，e.error不等于null。

为什么这种奇怪的行为？

代码：

  public partial class LoginForm : Form
{
    private static BackgroundWorker bw = new BackgroundWorker();
    private static ManualResetEvent mre = new ManualResetEvent(false);

    enum status
    {
        Blank,
        Success,
        Error
    };

    public LoginForm()
    {
        InterimProceedings();
        InitializeComponent();
    }

    private void InterimProceedings()
    {
        bw.DoWork += new DoWorkEventHandler(bw_DoWork);
        bw.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bw_RunWorkerCompleted);

        if (!bw.IsBusy)
        {
            bw.RunWorkerAsync();
        }
        else
        {
            throw new InvalidOperationException("BackgroundWorker is busy");
        }
    }

    private static void bw_DoWork(object sender, DoWorkEventArgs e)
    {
      //  Time taking task
          mre.Set();
    }

    private void bw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
    {
        if (!(e.Error == null))
        {
            this.lbl_status.Text = "Cannot proceed, Error occured";
            appStatus = status.Error;
        }
        else
        {
            this.lbl_status.Text = "Good to go...";
            appStatus = status.Success;
        }
    }

    private void btn_login_Click(object sender, EventArgs e)
    {
        mre.WaitOne();

        if(appStatus == status.Success)
        {
            // Proceed with intended work
        }

        else
        {
            // Pop-up error occurred
        }
    }

}

Answer 1

e.Error具有从DoWork抛出的异常。如果您在DoWork中使用try / catch，则没有例外。