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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