developer/Samples/NET Standard/ParallelExtensionsExtras_Standard/CoordinationDataStructures/ObservableConcurrentCollection.cs

   1 //--------------------------------------------------------------------------
   2 //
   3 //  Copyright (c) Microsoft Corporation.  All rights reserved.
   4 //
   5 //  File: ObservableConcurrentCollection.cs
   6 //
   7 //--------------------------------------------------------------------------
   8
   9 using System.Collections.Specialized;
  10 using System.ComponentModel;
  11 using System.Threading;
  12 using System.Diagnostics;
  13
  14 namespace System.Collections.Concurrent
  15 {
  16     /// <summary>
  17     /// Provides a thread-safe, concurrent collection for use with data binding.
  18     /// </summary>
  19     /// <typeparam name="T">Specifies the type of the elements in this collection.</typeparam>
  20     [DebuggerDisplay("Count={Count}")]
  21     [DebuggerTypeProxy(typeof(IProducerConsumerCollection_DebugView<>))]
  22     public class ObservableConcurrentCollection<T> :
  23         ProducerConsumerCollectionBase<T>, INotifyCollectionChanged, INotifyPropertyChanged
  24     {
  25         private readonly SynchronizationContext _context;
  26
  27         /// <summary>
  28         /// Initializes an instance of the ObservableConcurrentCollection class with an underlying
  29         /// queue data structure.
  30         /// </summary>
  31         public ObservableConcurrentCollection() : this(new ConcurrentQueue<T>()) { }
  32
  33         /// <summary>
  34         /// Initializes an instance of the ObservableConcurrentCollection class with the specified
  35         /// collection as the underlying data structure.
  36         /// </summary>
  37         public ObservableConcurrentCollection(IProducerConsumerCollection<T> collection) : base(collection)
  38         {
  39             _context = AsyncOperationManager.SynchronizationContext;
  40         }
  41
  42         /// <summary>Event raised when the collection changes.</summary>
  43         public event NotifyCollectionChangedEventHandler CollectionChanged;
  44         /// <summary>Event raised when a property on the collection changes.</summary>
  45         public event PropertyChangedEventHandler PropertyChanged;
  46
  47         /// <summary>
  48         /// Notifies observers of CollectionChanged or PropertyChanged of an update to the dictionary.
  49         /// </summary>
  50         private void NotifyObserversOfChange()
  51         {
  52             var collectionHandler = CollectionChanged;
  53             var propertyHandler = PropertyChanged;
  54             if (collectionHandler != null || propertyHandler != null)
  55             {
  56                 _context.Post(s =>
  57                 {
  58                     if (collectionHandler != null)
  59                     {
  60                         collectionHandler(this, new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
  61                     }
  62                     if (propertyHandler != null)
  63                     {
  64                         propertyHandler(this, new PropertyChangedEventArgs("Count"));
  65                     }
  66                 }, null);
  67             }
  68         }
  69
  70         protected override bool TryAdd(T item)
  71         {
  72             // Try to add the item to the underlying collection.  If we were able to,
  73             // notify any listeners.
  74             bool result = base.TryAdd(item);
  75             if (result) NotifyObserversOfChange();
  76             return result;
  77         }
  78
  79
  80         protected override bool TryTake(out T item)
  81         {
  82             // Try to remove an item from the underlying collection.  If we were able to,
  83             // notify any listeners.
  84             bool result = base.TryTake(out item);
  85             if (result) NotifyObserversOfChange();
  86             return result;
  87         }
  88     }
  89 }