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   1:

1   2: Module SyncExtensions

1   3:

1   4:     <System.Runtime.CompilerServices.Extension()> _

1   5:     Public Sub Sync(Of TItem)(ByVal targetItems As ICollection(Of TItem), ByVal sourceItems As IEnumerable(Of TItem))

1   6:         Dim o As Object = DirectCast(targetItems, ICollection).SyncRoot

1   7:         If Monitor.TryEnter(o, TimeSpan.FromSeconds(10)) Then

1   8:             ' Find items in source that are not in target

1   9:             Dim itemsToAdd As New Collection(Of TItem)

1  10:             For Each Item In sourceItems

1  11:                 If Not targetItems.Contains(Item) Then

1  12:                     itemsToAdd.Add(Item)

1  13:                 End If

1  14:             Next

1  15:             ' Apply all adds

1  16:             For Each Item In itemsToAdd

1  17:                 targetItems.Add(Item)

1  18:             Next

1  19:             ' Find tags in target that should not be in source

1  20:             Dim itemsToRemove As New Collection(Of TItem)

1  21:             For Each Item In targetItems

1  22:                 If Not sourceItems.Contains(Item) Then

1  23:                     itemsToRemove.Add(Item)

1  24:                 End If

1  25:             Next

1  26:             ' Apply all removes

1  27:             For Each Item In itemsToRemove

1  28:                 targetItems.Remove(Item)

1  29:             Next

1  30:             ' Dispose Timer

1  31:             Monitor.Exit(o)

1  32:         End If

1  33:     End Sub

1  34:

1  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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