等待BackgroundWorker RunWorkerCompleted

Question

在主线程中，我有一个计时器。在 Tick 事件中，我运行一个 BackgroundWorker。我在那里做了一些事情，然后 BackgroundWorker 调用 RunWorkerCompleted 事件。

在主线程中，我有函数 Stop。此函数禁用定时器。但我想在 BackgroundWorker 工作时等待他。

例如：

public void Next()
{

    // Start the asynchronous operation
    if (!this._backgroundWorker.IsBusy)
        this._backgroundWorker.RunWorkerAsync();

}

private void _backgroundWorker_DoWork(object sender, DoWorkEventArgs e)
{
    DoSomething();

}


private void _backgroundWorker_RunWorkerCompleted(object sender, 
    RunWorkerCompletedEventArgs e)
{
    DoSomethingElse();
}

public void Stop()
{
    this._timer.Enabled = false;
}

所以我的问题是如何等待BackgroundWorker的RunWorkerCompleted事件？我需要等到 DoSomethingElse(); 完成。

谢谢

Answer 1

处理 BackgroundWorker.RunWorkerCompleted 事件，该事件发生在后台操作已完成、已取消或引发异常。

// This event handler deals with the results of the
// background operation.

private void backgroundWorker1_RunWorkerCompleted(
    object sender, RunWorkerCompletedEventArgs e)
{
    // First, handle the case where an exception was thrown.
    if (e.Error != null)
    {
    }
    else if (e.Cancelled)
    {
        // Next, handle the case where the user canceled 
        // the operation.
        // Note that due to a race condition in 
        // the DoWork event handler, the Cancelled
        // flag may not have been set, even though
        // CancelAsync was called.
    }
    else
    {
        // Finally, handle the case where the operation 
        // succeeded.
    }

}

Answer 2

如果您只需要两个线程，请允许调用 this._backgroundWorker.RunWorkerAsync(); 的线程。
在调用此方法后死亡，并在 DoSomethingElse() 之后调用任何您想要发生的事情；在如下所示的同一块中

        private void _backgroundWorker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {

DoSomethingElse();
DoSomethingAfterSomethingElse();

        }

否则您将暂停一个线程以启动另一个线程然后返回，这违背了多线程的目的？

Answer 3

我认为BackgroundWorker.IsBusy 属性是在这种情况下唯一可以帮助您的成员。希望下面的逻辑能够满足您的需要。

//Add a class member
private bool stopped;

public void Stop() 
{    
     if (!this._backgroundWorker.IsBusy)
     {
         this._timer.Enabled = false; 
         stopped = false;
     }
     else
     {
         stopped = true;
     }

} 

private void _backgroundWorker_RunWorkerCompleted(object sender,      RunWorkerCompletedEventArgs e) 
{     
     DoSomethingElse(); 

    if (stopped)
    {
             this._timer.Enabled = false; 
             stopped = false;
    }
} 

Answer 4

这是一种停止/冻结主线程直到后台工作完成的方法：

public void Stop()
{
    if (!_backgroundWorker.IsBusy)
    {
        _timer.Enabled = false;

        // Stop/Freeze the main thread until the background worker finishes 
        while (_backgroundWorker.IsBusy)
        {
            Thread.Sleep(100);
        }
    }
}

现在，如果您的应用程序使用表单，我将禁用整个表单并显示消息，让用户知道应用程序正在等待进程完成。您还可以使用标志来禁止表单关闭。

private bool _canClose;

public void Stop()
{
    if (!_backgroundWorker.IsBusy)
    {
        _timer.Enabled = false;
        // Don't let the user do anything in the form until the background worker finishes
        this.IsEnabled = false;
        _label.Text = "Waiting for the process to finish";
        _canClose = false; 
    }
 }
private void _backgroundWorker_RunWorkerCompleted(object sender,
    RunWorkerCompletedEventArgs e)
{
    DoSomethingElse();
    // Allow the user to close the form
    this.IsEnabled = true;
    _canClose = true;
}

private void MainWindow_Closing(object sender, CancelEventArgs e)
{
    e.Cancel = !_canClose;
}