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ThreadSafeObservableCollection

, 17 Jun 2009 CPOL
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As part of an ongoing article I am just about to finish, I needed a thread safe ObservableCollection<T>. Now the native .NET framework doesn&#8217;t have one of those, but luckily it supplies you with the right job to create one using some of the Threading APIs.Here is what I came up with.

As part of an ongoing article I am just about to finish, I needed a thread safe ObservableCollection<T>. Now the native .NET framework doesn’t have one of those, but luckily it supplies you with the right job to create one using some of the Threading APIs.

Here is what I came up with.

   1:  /// <summary />
   2:  /// Provides a threadsafe ObservableCollection of T
   3:  /// </summary />
   4:  public class ThreadSafeObservableCollection<t />
   5:      : ObservableCollection<t />
   6:  {
   7:      #region Data
   8:      private Dispatcher _dispatcher;
   9:      private ReaderWriterLockSlim _lock;
  10:      #endregion
  11:  
  12:      #region Ctor
  13:      public ThreadSafeObservableCollection()
  14:      {
  15:          _dispatcher = Dispatcher.CurrentDispatcher;
  16:          _lock = new ReaderWriterLockSlim();
  17:      }
  18:      #endregion
  19:  
  20:  
  21:      #region Overrides
  22:  
  23:      /// <summary />
  24:      /// Clear all items
  25:      /// </summary />
  26:      protected override void ClearItems()
  27:      {
  28:          _dispatcher.InvokeIfRequired(() =>
  29:              {
  30:                  _lock.EnterWriteLock();
  31:                  try
  32:                  {
  33:                      base.ClearItems();
  34:                  }
  35:                  finally
  36:                  {
  37:                      _lock.ExitWriteLock();
  38:                  }
  39:              }, DispatcherPriority.DataBind);
  40:      }
  41:  
  42:      /// <summary />
  43:      /// Inserts an item
  44:      /// </summary />
  45:      protected override void InsertItem(int index, T item)
  46:      {
  47:          _dispatcher.InvokeIfRequired(() =>
  48:          {
  49:              if (index > this.Count)
  50:                  return;
  51:  
  52:              _lock.EnterWriteLock();
  53:              try
  54:              {
  55:                  base.InsertItem(index, item);
  56:              }
  57:              finally
  58:              {
  59:                  _lock.ExitWriteLock();
  60:              }
  61:          }, DispatcherPriority.DataBind);
  62:  
  63:      }
  64:  
  65:      /// <summary />
  66:      /// Moves an item
  67:      /// </summary />
  68:      protected override void MoveItem(int oldIndex, int newIndex)
  69:      {
  70:          _dispatcher.InvokeIfRequired(() =>
  71:          {
  72:              _lock.EnterReadLock();
  73:              Int32 itemCount = this.Count;
  74:              _lock.ExitReadLock();
  75:  
  76:              if (oldIndex >= itemCount |
  77:                  newIndex >= itemCount |
  78:                  oldIndex == newIndex)
  79:                  return;
  80:  
  81:              _lock.EnterWriteLock();
  82:              try
  83:              {
  84:                  base.MoveItem(oldIndex, newIndex);
  85:              }
  86:              finally
  87:              {
  88:                  _lock.ExitWriteLock();
  89:              }
  90:          }, DispatcherPriority.DataBind);
  91:  
  92:  
  93:  
  94:      }
  95:  
  96:      /// <summary />
  97:      /// Removes an item
  98:      /// </summary />
  99:      protected override void RemoveItem(int index)
 100:      {
 101:  
 102:          _dispatcher.InvokeIfRequired(() =>
 103:          {
 104:              if (index >= this.Count)
 105:                  return;
 106:  
 107:              _lock.EnterWriteLock();
 108:              try
 109:              {
 110:                  base.RemoveItem(index);
 111:              }
 112:              finally
 113:              {
 114:                  _lock.ExitWriteLock();
 115:              }
 116:          }, DispatcherPriority.DataBind);
 117:      }
 118:  
 119:      /// <summary />
 120:      /// Sets an item
 121:      /// </summary />
 122:      protected override void SetItem(int index, T item)
 123:      {
 124:          _dispatcher.InvokeIfRequired(() =>
 125:          {
 126:              _lock.EnterWriteLock();
 127:              try
 128:              {
 129:                  base.SetItem(index, item);
 130:              }
 131:              finally
 132:              {
 133:                  _lock.ExitWriteLock();
 134:              }
 135:          }, DispatcherPriority.DataBind);
 136:      }
 137:      #endregion
 138:  
 139:      #region Public Methods
 140:      /// <summary />
 141:      /// Return as a cloned copy of this Collection
 142:      /// </summary />
 143:      public T[] ToSyncArray()
 144:      {
 145:          _lock.EnterReadLock();
 146:          try
 147:          {
 148:              T[] _sync = new T[this.Count];
 149:              this.CopyTo(_sync, 0);
 150:              return _sync;
 151:          }
 152:          finally
 153:          {
 154:              _lock.ExitReadLock();
 155:          }
 156:      }
 157:      #endregion
 158:  }
 

It relies on this small extension method

   1:  /// <summary />
   2:  /// WPF Threading extension methods
   3:  /// </summary />
   4:  public static class WPFControlThreadingExtensions
   5:  {
   6:      #region Public Methods
   7:      /// <summary />
   8:      /// A simple WPF threading extension method, to invoke a delegate
   9:      /// on the correct thread if it is not currently on the correct thread
  10:      /// Which can be used with DispatcherObject types
  11:      /// </summary />
  12:      /// <param name="”disp”" />The Dispatcher object on which to do the Invoke</param />
  13:      /// <param name="”dotIt”" />The delegate to run</param />
  14:      /// <param name="”priority”" />The DispatcherPriority</param />
  15:      public static void InvokeIfRequired(this Dispatcher disp,
  16:          Action dotIt, DispatcherPriority priority)
  17:      {
  18:          if (disp.Thread != Thread.CurrentThread)
  19:          {
  20:              disp.Invoke(priority, dotIt);
  21:          }
  22:          else
  23:              dotIt();
  24:      }
  25:      #endregion
  26:  }
  

Hope it is useful to someone. Enjoy

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Sacha Barber
Software Developer (Senior)
United Kingdom United Kingdom
I currently hold the following qualifications (amongst others, I also studied Music Technology and Electronics, for my sins)
 
- MSc (Passed with distinctions), in Information Technology for E-Commerce
- BSc Hons (1st class) in Computer Science & Artificial Intelligence
 
Both of these at Sussex University UK.
 
Award(s)

I am lucky enough to have won a few awards for Zany Crazy code articles over the years

  • Microsoft C# MVP 2014
  • Codeproject MVP 2014
  • Microsoft C# MVP 2013
  • Codeproject MVP 2013
  • Microsoft C# MVP 2012
  • Codeproject MVP 2012
  • Microsoft C# MVP 2011
  • Codeproject MVP 2011
  • Microsoft C# MVP 2010
  • Codeproject MVP 2010
  • Microsoft C# MVP 2009
  • Codeproject MVP 2009
  • Microsoft C# MVP 2008
  • Codeproject MVP 2008
  • And numerous codeproject awards which you can see over at my blog

Comments and Discussions

 
GeneralMy vote of 1 Pinmemberjaruifer23-Dec-09 4:35 
GeneralThanks for sharing PinmemberBishoy Ghaly22-Jun-09 22:38 
GeneralRe: Thanks for sharing PinmvpSacha Barber22-Jun-09 23:40 
Generalcouple of suggestions/questions PinmemberItay Sagui17-Jun-09 4:34 
GeneralRe: couple of suggestions/questions PinmvpSacha Barber17-Jun-09 8:47 

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