Reversing an ObservableCollection using linq

Question

This one should be easy, and im ashamed i havent figured it out myself yet. I'm trying to reverse the order of a list of items in my wp7 app. The list is an ObservableCollection. When using system.linq, intellisense lets me do this: myList.Reverse(); ,but this doesnt seem to work. Am i doing something wrong, or is there some other way i can do this easily?

Thanks in advance.

"Doesn't seem to work", how? Do you mean the UI doesn't show the items in reversed order? — user7116, Jul 10 '12 at 22:17
Related question, but not necessarily a duplicate http://stackoverflow.com/questions/10413535/reverse-order-of-observablecollection — user7116, Jul 10 '12 at 22:22

score 34 · Accepted Answer · answered Jul 10 '12 at 23:05

34

Reverse returns an IEnumerable, it does not modify the collection. To modify the collection you could do

collection = new ObservableCollection<YourType>(collection.Reverse());

answered Jul 10 '12 at 23:05

Shawn Kendrot

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2

Thats the kind of solution i was looking for. And it worked like a charm. Thanks! – Hans Petter Naumann Jul 11 '12 at 04:49
How can this work, when collection is an ObservableCollection? That class has no Reverse...? At least, that's the message I get when I try this. – Erik Apr 25 '15 at 08:55
3

Reverse is an extension method within the System.Linq.Enumerable class. Add the using statement for System.Linq; – Shawn Kendrot Apr 26 '15 at 01:56

Maxence · Answer 2 · 2015-03-20T10:25:35.853

4

If you don't want to recreate the collection:

for (int i = 0; i < collection.Count; i++)
  collection.Move(collection.Count - 1, i);

edited Mar 20 '15 at 10:25

answered Mar 07 '15 at 20:36

Maxence

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score 0 · Answer 3 · answered Jul 10 '12 at 22:31

make a class that inherits the observablecollection(of T) and implement a sort object in it. This is a vb.net brute force way of doing that:

    Public Sub Sort(ByVal comparer As IComparer(Of T))
    Dim j As Integer
    Dim index As T
    For i As Integer = 1 To Count - 1
        index = Me(i)
        j = i
        While (j > 0) AndAlso (comparer.Compare(Me(j - 1), index) = 1)
            Me(j) = Me(j - 1)
            j = j - 1
        End While
        Me(j) = index
    Next
End Sub

Reversing an ObservableCollection using linq

3 Answers3