wpf - 快速执行且线程安全的可观察集合

Question

ObservableCollection 会针对对其执行的每个操作发出通知。首先，它们没有批量添加或删除调用，其次它们不是线程安全的。

这不会让他们变慢吗？我们不能有更快的替代方案吗？有人说包裹着 ObservableCollection 的 ICollectionView 速度很快？此说法的真实性如何。

Answer 1

ObservableCollection 可以很快，如果它愿意的话。 :-)

下面的代码是线程安全、更快的可观察集合的一个很好的示例，您可以根据自己的意愿进一步扩展它。

using System.Collections.Specialized;

public class FastObservableCollection<T> : ObservableCollection<T>
{
    private readonly object locker = new object();

    /// <summary>
    /// This private variable holds the flag to
    /// turn on and off the collection changed notification.
    /// </summary>
    private bool suspendCollectionChangeNotification;

    /// <summary>
    /// Initializes a new instance of the FastObservableCollection class.
    /// </summary>
    public FastObservableCollection()
        : base()
    {
        this.suspendCollectionChangeNotification = false;
    }

    /// <summary>
    /// This event is overriden CollectionChanged event of the observable collection.
    /// </summary>
    public override event NotifyCollectionChangedEventHandler CollectionChanged;

    /// <summary>
    /// This method adds the given generic list of items
    /// as a range into current collection by casting them as type T.
    /// It then notifies once after all items are added.
    /// </summary>
    /// <param name="items">The source collection.</param>
    public void AddItems(IList<T> items)
    {
       lock(locker)
       {
          this.SuspendCollectionChangeNotification();
          foreach (var i in items)
          {
             InsertItem(Count, i);
          }
          this.NotifyChanges();
       }
    }

    /// <summary>
    /// Raises collection change event.
    /// </summary>
    public void NotifyChanges()
    {
        this.ResumeCollectionChangeNotification();
        var arg
             = new NotifyCollectionChangedEventArgs
                  (NotifyCollectionChangedAction.Reset);
        this.OnCollectionChanged(arg);
    }

    /// <summary>
    /// This method removes the given generic list of items as a range
    /// into current collection by casting them as type T.
    /// It then notifies once after all items are removed.
    /// </summary>
    /// <param name="items">The source collection.</param>
    public void RemoveItems(IList<T> items)
    {
        lock(locker)
        {
           this.SuspendCollectionChangeNotification();
           foreach (var i in items)
           {
             Remove(i);
           }
           this.NotifyChanges();
        }
    }

    /// <summary>
    /// Resumes collection changed notification.
    /// </summary>
    public void ResumeCollectionChangeNotification()
    {
        this.suspendCollectionChangeNotification = false;
    }

    /// <summary>
    /// Suspends collection changed notification.
    /// </summary>
    public void SuspendCollectionChangeNotification()
    {
        this.suspendCollectionChangeNotification = true;
    }

    /// <summary>
    /// This collection changed event performs thread safe event raising.
    /// </summary>
    /// <param name="e">The event argument.</param>
    protected override void OnCollectionChanged(NotifyCollectionChangedEventArgs e)
    {
        // Recommended is to avoid reentry 
        // in collection changed event while collection
        // is getting changed on other thread.
        using (BlockReentrancy())
        {
            if (!this.suspendCollectionChangeNotification)
            {
                NotifyCollectionChangedEventHandler eventHandler = 
                      this.CollectionChanged;
                if (eventHandler == null)
                {
                    return;
                }

                // Walk thru invocation list.
                Delegate[] delegates = eventHandler.GetInvocationList();

                foreach
                (NotifyCollectionChangedEventHandler handler in delegates)
                {
                    // If the subscriber is a DispatcherObject and different thread.
                    DispatcherObject dispatcherObject
                         = handler.Target as DispatcherObject;

                    if (dispatcherObject != null
                           && !dispatcherObject.CheckAccess())
                    {
                        // Invoke handler in the target dispatcher's thread... 
                        // asynchronously for better responsiveness.
                        dispatcherObject.Dispatcher.BeginInvoke
                              (DispatcherPriority.DataBind, handler, this, e);
                    }
                    else
                    {
                        // Execute handler as is.
                        handler(this, e);
                    }
                }
            }
        }
    }
}

此外，位于 ObservableCollection 之上的 ICollectionView 会主动感知更改，并与任何其他源列表相比相对较快地执行过滤、分组和排序。

同样，可观察集合可能不是更快数据更新的完美答案，但它们的工作做得很好。