如何处理具有异步方法的对象？

Question

我有这个PreloadClient实现的对象IDisposable,我想处理它,但在异步方法完成它们的调用之后......这没有发生

    private void Preload(SlideHandler slide)
    {
        using(PreloadClient client = new PreloadClient())
        {                 
             client.PreloadCompleted += client_PreloadCompleted;
             client.Preload(slide);
        }
        // Here client is disposed immediately
    }
    private void client_PreloadCompleted(object sender, SlidePreloadCompletedEventArgs e)
    {
     // this is method is called after a while, 
     // but errors are thrown when trying to access object state (fields, properties)
    }

那么,任何想法或工作？

Answer 1

1. 您不应该使用该using构造,而是在不再需要它们时处置它们:

   // keep a list of strong references to avoid garbage collection,
   // and dispose them all in case we're disposing the encapsulating object
   private readonly List<PreloadClient> _activeClients = new List<PreloadClient>();
   private void Preload(SlideHandler slide)
   {
       PreloadClient client = new PreloadClient();
       _activeClients.Add(client);
       client.PreloadCompleted += client_PreloadCompleted;
       client.Preload(slide);
   }
   
   private void client_PreloadCompleted(object sender,
        SlidePreloadCompletedEventArgs e)
   {
       PreloadClient client = sender as PreloadClient;
   
       // do stuff
   
       client.PreloadCompleted -= client_PreloadCompleted;
       client.Dispose();
       _activeClients.Remove(client);
   }
   

2. 在这种情况下,您必须在处置主类时处置所有客户端:

   protected override Dispose(bool disposing)
   {
       foreach (PreloadClient client in _activeClients)
       { 
           client.PreloadCompleted -= client_PreloadCompleted;
           client.Dispose();
       }
       _activeClients.Clear();
       base.Dispose(disposing);
   }
   

3. 请注意,此实现不是线程安全的

   • 访问_activeClients列表必须是线程安全的,因为PreloadCompleted从另一个线程调用您的方法
   • 您的包含对象可能会在客户端触发事件之前处理.在这种情况下,"做东西"应该什么都不做,所以这是你应该照顾的另一件事.
   • 在事件处理程序中使用try/ finallyblock 可能是个好主意,以确保在所有情况下都可以处置该对象