wpf 快速执行和线程安全的可观察集合

Fast performing and thread safe observable collection

提问by WPF-it

ObservableCollections raise notifications for each action performed on them. Firstly they dont have bulk add or remove calls, secondly they are not thread safe.

ObservableCollections 为对它们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。

Doesn't this make them slower? Cant we have a faster alternative? Some say ICollectionViewwrapped around an ObservableCollectionis fast? How trueis this claim.

这不会让他们变慢吗？我们不能有更快的选择吗？有人说ICollectionView缠一个ObservableCollection是快？这种说法有多真实。

回答by WPF-it

ObservableCollectioncan be fast, if it wantsto. :-)

ObservableCollection如果它愿意，可以很快。:-)

The code below is a very good example of a thread safe, faster observable collection and you can extend it further to your wish.

下面的代码是线程安全、更快的可观察集合的一个很好的例子，您可以根据需要进一步扩展它。

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);
                    }
                }
            }
        }
    }
}

Also ICollectionViewthat sits above the ObservableCollectionis actively aware of the changes and performs filtering, grouping, sorting relatively fast as compared to any other source list.

此外ICollectionView，ObservableCollection与任何其他源列表相比，它主动了解更改并执行过滤、分组、排序相对较快。

Again observable collections may not be a perfectanswer for faster data updates but they do their job pretty well.

同样，可观察的集合对于更快的数据更新可能不是一个完美的答案，但它们做得很好。

回答by norekhov

Here is a compilation of some solutions which I made. The idea of collection changed invokation taken from first answer.

这是我制作的一些解决方案的汇编。收集的想法改变了从第一个答案中获取的调用。

Also seems that "Reset" operation should be synchronous with main thread otherwise strange things happen to CollectionView and CollectionViewSource.

似乎“重置”操作应该与主线程同步，否则 CollectionView 和 CollectionViewSource 会发生奇怪的事情。

I think that's because on "Reset" handler tries to read the collection contents immediately and they should be already in place. If you do "Reset" async and than immediately add some items also async than newly added items might be added twice.

我认为这是因为在“重置”处理程序尝试立即读取集合内容并且它们应该已经就位。如果您执行“重置”异步操作，然后立即添加一些项目，那么新添加的项目可能会被添加两次。

public interface IObservableList<T> : IList<T>, INotifyCollectionChanged
{
}

public class ObservableList<T> : IObservableList<T>
{
    private IList<T> collection = new List<T>();
    public event NotifyCollectionChangedEventHandler CollectionChanged;
    private ReaderWriterLock sync = new ReaderWriterLock();

    protected virtual void OnCollectionChanged(NotifyCollectionChangedEventArgs args)
    {
        if (CollectionChanged == null)
            return;
        foreach (NotifyCollectionChangedEventHandler handler in CollectionChanged.GetInvocationList())
        {
            // If the subscriber is a DispatcherObject and different thread.
            var dispatcherObject = handler.Target as DispatcherObject;

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

    public ObservableList()
    {
    }

    public void Add(T item)
    {
        sync.AcquireWriterLock(Timeout.Infinite);
        try
        {
            collection.Add(item);
            OnCollectionChanged(
                    new NotifyCollectionChangedEventArgs(
                      NotifyCollectionChangedAction.Add, item));
        }
        finally
        {
            sync.ReleaseWriterLock();
        }
    }

    public void Clear()
    {
        sync.AcquireWriterLock(Timeout.Infinite);
        try
        {
            collection.Clear();
            OnCollectionChanged(
                    new NotifyCollectionChangedEventArgs(
                        NotifyCollectionChangedAction.Reset));
        }
        finally
        {
            sync.ReleaseWriterLock();
        }
    }

    public bool Contains(T item)
    {
        sync.AcquireReaderLock(Timeout.Infinite);
        try
        {
            var result = collection.Contains(item);
            return result;
        }
        finally
        {
            sync.ReleaseReaderLock();
        }
    }

    public void CopyTo(T[] array, int arrayIndex)
    {
        sync.AcquireWriterLock(Timeout.Infinite);
        try
        {
            collection.CopyTo(array, arrayIndex);
        }
        finally
        {
            sync.ReleaseWriterLock();
        }
    }

    public int Count
    {
        get
        {
            sync.AcquireReaderLock(Timeout.Infinite);
            try
            {
                return collection.Count;
            }
            finally
            {
                sync.ReleaseReaderLock();
            }
        }
    }

    public bool IsReadOnly
    {
        get { return collection.IsReadOnly; }
    }

    public bool Remove(T item)
    {
        sync.AcquireWriterLock(Timeout.Infinite);
        try
        {
            var index = collection.IndexOf(item);
            if (index == -1)
                return false;
            var result = collection.Remove(item);
            if (result)
                OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Remove, item, index));
            return result;
        }
        finally
        {
            sync.ReleaseWriterLock();
        }
    }

    public IEnumerator<T> GetEnumerator()
    {
        return collection.GetEnumerator();
    }

    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
    {
        return collection.GetEnumerator();
    }

    public int IndexOf(T item)
    {
        sync.AcquireReaderLock(Timeout.Infinite);
        try
        {
            var result = collection.IndexOf(item);
            return result;
        }
        finally
        {
            sync.ReleaseReaderLock();
        }
    }

    public void Insert(int index, T item)
    {
        sync.AcquireWriterLock(Timeout.Infinite);
        try
        {
            collection.Insert(index, item);
            OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Add, item, index));
        }
        finally
        {
            sync.ReleaseWriterLock();
        }
    }

    public void RemoveAt(int index)
    {
        sync.AcquireWriterLock(Timeout.Infinite);
        try
        {
            if (collection.Count == 0 || collection.Count <= index)
                return;
            var item = collection[index];
            collection.RemoveAt(index);
            OnCollectionChanged(
                    new NotifyCollectionChangedEventArgs(
                       NotifyCollectionChangedAction.Remove, item, index));
        }
        finally
        {
            sync.ReleaseWriterLock();
        }
    }

    public T this[int index]
    {
        get
        {
            sync.AcquireReaderLock(Timeout.Infinite);
            try
            {
                var result = collection[index];
                return result;
            }
            finally
            {
                sync.ReleaseReaderLock();
            }
        }
        set
        {
            sync.AcquireWriterLock(Timeout.Infinite);
            try
            {
                if (collection.Count == 0 || collection.Count <= index)
                    return;
                var item = collection[index];
                collection[index] = value;
                OnCollectionChanged(
                        new NotifyCollectionChangedEventArgs(
                           NotifyCollectionChangedAction.Replace, value, item, index));
            }
            finally
            {
                sync.ReleaseWriterLock();
            }
        }

    }
}

回答by jsirr13

I can't add comments because I'm not cool enough yet, but sharing this issue I ran into is probably worth posting even though it's not really an answer. I kept getting an "Index was out of range" exception using this FastObservableCollection, because of the BeginInvoke. Apparently changes being notified can be undone before the handler is called, so to fix this I passed the following as the fourth parameter for the BeginInvoke called from the OnCollectionChanged method (as opposed to using the event args one):

我无法添加评论，因为我还不够酷，但是分享我遇到的这个问题可能值得发布，即使它不是真正的答案。由于BeginInvoke，我使用此FastObservableCollection 不断收到“索引超出范围”异常。显然，可以在调用处理程序之前撤消被通知的更改，因此为了解决此问题，我将以下内容作为从 OnCollectionChanged 方法调用的 BeginInvoke 的第四个参数传递（而不是使用事件参数一）：

dispatcherObject.Dispatcher.BeginInvoke
                          (DispatcherPriority.DataBind, handler, this, new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));

Instead of this:

取而代之的是：

dispatcherObject.Dispatcher.BeginInvoke
                          (DispatcherPriority.DataBind, handler, this, e);

This fixed the "Index was out of range" issue I was running into. Here's a more detailed explaination / code snpipet: Where do I get a thread-safe CollectionView?

这解决了我遇到的“索引超出范围”问题。这是更详细的解释/代码snpipet：我从哪里获得线程安全的CollectionView？

回答by Raul

An example where is created a synchronized Observable list:

创建同步 Observable 列表的示例：

newSeries = new XYChart.Series<>();
ObservableList<XYChart.Data<Number, Number>> listaSerie;
listaSerie = FXCollections.synchronizedObservableList(FXCollections.observableList(new ArrayList<XYChart.Data<Number, Number>>()));
newSeries.setData(listaSerie);