Sync extension for Lists/Collections or whatever

I recently found the need to Sync two lists. I have one list that is used for display, and I want to dynamically sync that list with a new one by applying a delta.

I thought that this would be difficult, but I was surprised at its ease.

   1: 

   2: Module SyncExtensions

   3: 

   4:     <System.Runtime.CompilerServices.Extension()> _

   5:     Public Sub Sync(Of TItem)(ByVal targetItems As ICollection(Of TItem), ByVal sourceItems As IEnumerable(Of TItem))

   6:         Dim o As Object = DirectCast(targetItems, ICollection).SyncRoot

   7:         If Monitor.TryEnter(o, TimeSpan.FromSeconds(10)) Then

   8:             ' Find items in source that are not in target

   9:             Dim itemsToAdd As New Collection(Of TItem)

  10:             For Each Item In sourceItems

  11:                 If Not targetItems.Contains(Item) Then

  12:                     itemsToAdd.Add(Item)

  13:                 End If

  14:             Next

  15:             ' Apply all adds

  16:             For Each Item In itemsToAdd

  17:                 targetItems.Add(Item)

  18:             Next

  19:             ' Find tags in target that should not be in source

  20:             Dim itemsToRemove As New Collection(Of TItem)

  21:             For Each Item In targetItems

  22:                 If Not sourceItems.Contains(Item) Then

  23:                     itemsToRemove.Add(Item)

  24:                 End If

  25:             Next

  26:             ' Apply all removes

  27:             For Each Item In itemsToRemove

  28:                 targetItems.Remove(Item)

  29:             Next

  30:             ' Dispose Timer

  31:             Monitor.Exit(o)

  32:         End If

  33:     End Sub

  34: 

  35: End Module

You need to remember to lock the object while you sync. This is to allow your threading to take place without incident. The nitty gritty is just a case of comparing the two lists and building a list of changes to make and then removing them :)

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