What is the most efficient method for looping through a SortedList in VB 2008?

Question

The code below shows me (I think) that the "for each" loop is about 10% faster than the "i to n" loop, but the "for each" loop creates 567k in new memory? Is this right? Which way is generally most efficient with regards to speed and memory usage?

If you want to run this code in VB just add a button and 2 labels to a form.

Public Class StateObject
    Public WorkSocket As String = "FFFFFFFFFFFF"
    Public BufferSize As Integer = 32767
    Public Buffer(32767) As Byte
End Class

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    For cnt As Integer = 1 To 250
        Dim StateObjecter As New StateObject
        ClientNetList.Add(cnt.ToString, StateObjecter)
    Next
End Sub


Private ClientNetList As New SortedList(Of String, StateObject)
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    Dim stop1 As New Stopwatch
    Dim stop2 As New Stopwatch

    Dim TotalMemory1 As Integer = GC.GetTotalMemory(False)
    stop1.Start()
    For cnt As Integer = 1 To 1000000
        For i = 0 To ClientNetList.Count - 1
            ClientNetList.Values(i).WorkSocket = "FFF"
        Next

    Next
    stop1.Stop()
    Dim TotalMemory2 As Integer = GC.GetTotalMemory(False)
    MsgBox(TotalMemory2 - TotalMemory1)

    TotalMemory1 = GC.GetTotalMemory(False)
    Dim fff As Integer = GC.GetGeneration(ClientNetList)
    stop2.Start()
    For cnt As Integer = 1 To 1000000
        For Each ValueType As StateObject In ClientNetList.Values
            ValueType.WorkSocket = "FFF"
        Next
    Next
    stop2.Stop()

    Dim ffff As Integer = GC.GetGeneration(ClientNetList)
    TotalMemory2 = GC.GetTotalMemory(False)
    MsgBox(TotalMemory2 - TotalMemory1)

    Label1.Text = "i: " & stop1.ElapsedMilliseconds
    Label2.Text = "e: " & stop2.ElapsedMilliseconds
End Sub

Answer 1

On my system the "for i = 1 " loop was faster for the first test (the first click of the button of the program run) by about 20 percent. But the "for each" loop was a hair faster on subsequent tests. The "for each" loop took a little more memory, but this is temporary and will be eventually garbage collected.

The pros and cons of "for each" and "for i = " have been debated here. For each is nice because it works with structures other than arrays, and makes an object available. "For i =" has the advantage of designating the bounds and order of array items in the loop, and avoids a bug you can encounter with arrays:

Dim a(50) As Integer
Dim i As Integer
For Each i In a
  i = 22
  Next i

In this example, the array is never initialized to 22. The variable i is just a copy of an array element, and the original array element is not changed when i is assigned 22.