49

我正在编写一个在辅助线程上执行连续循环操作的 Visual C# 程序。有时,当该线程完成任务时,我希望它触发事件处理程序。我的程序会这样做,但是当事件处理程序被触发时,辅助线程会等到事件处理程序完成后再继续线程。我如何让它继续?这是我目前的结构方式......

class TestClass 
{
  private Thread SecondaryThread;
  public event EventHandler OperationFinished;

  public void StartMethod()
  {
    ...
    SecondaryThread.Start();      //start the secondary thread
  }

  private void SecondaryThreadMethod()
  {
    ...
    OperationFinished(null, new EventArgs());
    ...  //This is where the program waits for whatever operations take
         //place when OperationFinished is triggered.
  }

}

此代码是我的一台设备的 API 的一部分。当 OperationFinished 事件被触发时,我希望客户端应用程序能够做它需要做的任何事情(即相应地更新 GUI),而无需拖拽 API 操作。

另外,如果我不想将任何参数传递给事件处理程序,我的语法是否正确OperationFinished(null, new EventArgs())

4

7 回答 7

65

所以你想以一种防止监听器阻塞后台线程的方式引发事件?给我几分钟的时间来举个例子;这很简单:-)

我们开始吧: 首先是一个重要的注意事项!无论何时调用BeginInvoke都必须调用对应的EndInvoke,否则如果调用的方法抛出异常返回值,则 ThreadPool 线程将永远不会释放回池中,从而导致线程泄漏!

class TestHarness
{

    static void Main(string[] args)
    {
        var raiser = new SomeClass();

        // Emulate some event listeners
        raiser.SomeEvent += (sender, e) => { Console.WriteLine("   Received event"); };
        raiser.SomeEvent += (sender, e) =>
        {
            // Bad listener!
            Console.WriteLine("   Blocking event");
            System.Threading.Thread.Sleep(5000);
            Console.WriteLine("   Finished blocking event");
        };

        // Listener who throws an exception
        raiser.SomeEvent += (sender, e) =>
        {
            Console.WriteLine("   Received event, time to die!");
            throw new Exception();
        };

        // Raise the event, see the effects
        raiser.DoSomething();

        Console.ReadLine();
    }
}

class SomeClass
{
    public event EventHandler SomeEvent;

    public void DoSomething()
    {
        OnSomeEvent();
    }

    private void OnSomeEvent()
    {
        if (SomeEvent != null)
        {
            var eventListeners = SomeEvent.GetInvocationList();

            Console.WriteLine("Raising Event");
            for (int index = 0; index < eventListeners.Count(); index++)
            {
                var methodToInvoke = (EventHandler)eventListeners[index];
                methodToInvoke.BeginInvoke(this, EventArgs.Empty, EndAsyncEvent, null);
            }
            Console.WriteLine("Done Raising Event");
        }
    }

    private void EndAsyncEvent(IAsyncResult iar)
    {
        var ar = (System.Runtime.Remoting.Messaging.AsyncResult)iar;
        var invokedMethod = (EventHandler)ar.AsyncDelegate;

        try
        {
            invokedMethod.EndInvoke(iar);
        }
        catch
        {
            // Handle any exceptions that were thrown by the invoked method
            Console.WriteLine("An event listener went kaboom!");
        }
    }
}
于 2009-12-16T17:26:12.623 回答
17

使用任务并行库,现在可以执行以下操作:

Task.Factory.FromAsync( ( asyncCallback, @object ) => this.OperationFinished.BeginInvoke( this, EventArgs.Empty, asyncCallback, @object ), this.OperationFinished.EndInvoke, null );
于 2013-05-02T11:00:29.267 回答
12

另外,如果我不想将任何参数传递给事件处理程序,使用 OperationFinished(null, new EventArgs()) 我的语法是否正确?

不。通常,您将其称为:

OperationFinished(this, EventArgs.Empty);

您应该始终将对象作为发件人传递 - 它在模式中是预期的(尽管通常被忽略)。EventArgs.Empty 也比 new EventArgs() 好。

为了在单独的线程中触发它,最简单的选择可能是只使用线程池:

private void RaiseOperationFinished()
{
       ThreadPool.QueueUserWorkItem( new WaitCallback( (s) =>
           {
              if (this.OperationFinished != null)
                   this.OperationFinished(this, EventArgs.Empty);
           }));
}

话虽如此,在单独的线程上引发事件是应该彻底记录的,因为它可能会导致意外行为。

于 2009-12-16T17:13:09.790 回答
6

尝试事件委托上的 BeginInvoke 和 EndInvoke 方法 - 这些方法会立即返回,并允许您使用轮询、等待句柄或回调函数在方法完成时通知您。请参阅此处了解概览;在您的示例中,事件是您将使用的委托

于 2009-12-16T17:17:52.513 回答
4

也许下面的 Method2 或 Method3 可以提供帮助:)

public partial class Form1 : Form
{
    private Thread SecondaryThread;

    public Form1()
    {
        InitializeComponent();

        OperationFinished += callback1;
        OperationFinished += callback2;
        OperationFinished += callback3;
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        SecondaryThread = new Thread(new ThreadStart(SecondaryThreadMethod));
        SecondaryThread.Start();
    }

     private void SecondaryThreadMethod()
     {
        Stopwatch sw = new Stopwatch();
        sw.Restart();

        OnOperationFinished(new MessageEventArg("test1"));
        OnOperationFinished(new MessageEventArg("test2"));
        OnOperationFinished(new MessageEventArg("test3"));
        //This is where the program waits for whatever operations take
             //place when OperationFinished is triggered.

        sw.Stop();

        Invoke((MethodInvoker)delegate
        {
            richTextBox1.Text += "Time taken (ms): " + sw.ElapsedMilliseconds + "\n";
        });
     }

    void callback1(object sender, MessageEventArg e)
    {
        Thread.Sleep(2000);
        Invoke((MethodInvoker)delegate
        {
            richTextBox1.Text += e.Message + "\n";
        });
    }
    void callback2(object sender, MessageEventArg e)
    {
        Thread.Sleep(2000);
        Invoke((MethodInvoker)delegate
        {
            richTextBox1.Text += e.Message + "\n";
        });
    }

    void callback3(object sender, MessageEventArg e)
    {
        Thread.Sleep(2000);
        Invoke((MethodInvoker)delegate
        {
            richTextBox1.Text += e.Message + "\n";
        });
    }

    public event EventHandler<MessageEventArg> OperationFinished;

    protected void OnOperationFinished(MessageEventArg e)
    {
        //##### Method1 - Event raised on the same thread ##### 
        //EventHandler<MessageEventArg> handler = OperationFinished;

        //if (handler != null)
        //{
        //    handler(this, e);
        //}

        //##### Method2 - Event raised on (the same) separate thread for all listener #####
        //EventHandler<MessageEventArg> handler = OperationFinished;

        //if (handler != null)
        //{
        //    Task.Factory.StartNew(() => handler(this, e));
        //}

        //##### Method3 - Event raised on different threads for each listener #####
        if (OperationFinished != null)
        {
            foreach (EventHandler<MessageEventArg> handler in OperationFinished.GetInvocationList())
            {
                Task.Factory.FromAsync((asyncCallback, @object) => handler.BeginInvoke(this, e, asyncCallback, @object), handler.EndInvoke, null);
            }
        }
    }
}

public class MessageEventArg : EventArgs
{
    public string Message { get; set; }

    public MessageEventArg(string message)
    {
        this.Message = message;
    }
}

}

于 2015-02-24T04:36:51.100 回答
0

查看BackgroundWorker类。我认为它完全符合您的要求。

编辑:我认为您要问的是如何在仅完成整个后台任务的一小部分时触发事件。BackgroundWorker 提供了一个名为“ProgressChanged”的事件,允许您向主线程报告整个过程的某些部分已完成。然后,当所有异步工作完成时,它会引发“RunWorkerCompleted”事件。

于 2009-12-16T17:08:01.350 回答
0

我更喜欢将我传递给子线程的方法定义为更新 UI 的委托。首先定义一个委托:

public delegate void ChildCallBackDelegate();

在子线程中定义一个委托成员:

public ChildCallbackDelegate ChildCallback {get; set;}

在调用类中定义更新 UI 的方法。您需要将它包装在目标控件的调度程序中,因为它是从单独的线程中调用的。注意 BeginInvoke。在这种情况下,不需要 EndInvoke:

private void ChildThreadUpdater()
{
  yourControl.Dispatcher.BeginInvoke(System.Windows.Threading.DispatcherPriority.Background
    , new System.Threading.ThreadStart(delegate
      {
        // update your control here
      }
    ));
}

在启动子线程之前,设置它的 ChildCallBack 属性:

theChild.ChildCallBack = new ChildCallbackDelegate(ChildThreadUpdater);

然后当子线程想要更​​新父线程时:

ChildCallBack();
于 2009-12-16T23:29:51.783 回答