Is it possible to do a For…Each Loop Backwards?

Question

I don\'t believe this is possible by conventional methods, but something like this verbose code:

For Each s As String In myStringList Step -1
    //\' Do stu         


        

Answer 1

Call the System.Linq.Enumerable.Reverse method to get an IEnuemrable(Of TSource) in the reverse order of your enumerable source.

Answer 2

For Each s As String In myStringList.Reverse
    //' Do stuff here
Next

Answer 3

Sadly, the MSDN docs on For Each state that the For Each construct is there explicitly for cases where the order of the iteration is unimportant (unordered sets and the like). So there is unfortunately no concept of reversing a For Each, as the order is not defined anyway.

Good luck!

Answer 4

Testig in Framework 4, the code

For Each s As String In myStringList.Reverse
    //' Do stuff here
Next

it wasn't working, the right way to do it is:

myStringList.Reverse() ' it is a method not a function
For Each s As String In myStringList
//' Do stuff here
Next

Look at: MSDN: Reserve

Answer 5

You can add a extended function to the class you are trying to reverse

<Serializable()> Public Class SomeCollection
    Inherits CollectionBase
    Public Sub New()
    End Sub

    Public Sub Add(ByVal Value As Something)
        Me.List.Add(Value)
    End Sub

    Public Sub Remove(ByVal Value As Something)
        Me.List.Remove(Value)
    End Sub

    Public Function Contains(ByVal Value As Something) As Boolean
        Return Me.List.Contains(Value)
    End Function

    Public Function Item(ByVal Index As Integer) As Something
        Return DirectCast(Me.List.Item(Index), Something)
    End Function

    Public Function Reverse() As SomeCollection
        Dim revList As SomeCollection = New SomeCollection()
        For index As Integer = (Me.List.Count - 1) To 0 Step -1
             revList.List.Add(Me.List.Item(index))
        Next
        Return revList
    End Function
End Class

Then you would call it like this

For Each s As Something In SomeCollection.Reverse

Next

Answer 6

What you have to do is create an array with your for each you had before, then use array.reverse and run the for each on the array. Done

Cheers