Is there a list (of string) or equivalent in VB that I can configure to only hold x entries and then overwrite oldest

Question

Is there a list (of string) or equivalent in VB that I can configure to only hold x entries and then overwrite oldest each time I add something new to it?

e.g. I can set it to hold say 25 items, and then if I add a 26th item it overwrites the first item and so on

Answer 1

HI,
you create your own list class like in following console demo. Add insert item at the top of list.

Module Module64  
  Sub Main()  
    Try  
      Call (New Demo).Execute()  
    Catch ex As Exception  
      Console.WriteLine(ex.ToString)  
    End Try  
    Console.WriteLine("Continue enter key")  
    Console.ReadKey()  
  End Sub  
  
  Friend Class Demo  
    Friend Sub Execute()  
      Dim itemList As New MyList(Of String)(5)  
      For i = 1 To 7  
        itemList.Add($"Item {i}")  
      Next  
      For Each item In itemList  
        Console.WriteLine(item)  
      Next  
    End Sub  
  End Class  
  
  Friend Class MyList(Of T)  
    Inherits List(Of T)  
  
    Private _maxCount As Integer  
    Public Sub New(maxCount As Integer)  
      Me._maxCount = maxCount  
    End Sub  
  
    Friend Shadows Sub Add(item As T)  
      Me.Insert(0, item)  
      If Me.Count > Me._maxCount Then Me.RemoveAt(Me.Count - 1)  
    End Sub  
  End Class  
  
End Module  

Result:

Answer 2

Circular Lists

The Class

    ''' <summary>
    ''' a list with a limit
    ''' </summary>
    ''' <typeparam name="T">the type of data</typeparam>
    ''' <remarks></remarks>
    Public Class ListLimit(Of T)
        Private _max As Integer = 0
        Private _List As New List(Of T)
        Private _pos As Integer = 0
        Private _NewLast As Boolean = True
        ''' <summary>
        ''' list with max entires
        ''' </summary>
        ''' <param name="MaxEntries">maximum entries in list</param>
        ''' <param name="NewLast">True if new items added to end, False if new entries added to beginning</param>
        ''' <remarks></remarks>
        Public Sub New(MaxEntries As Integer,
                       Optional NewLast As Boolean = True)
            Me._max = MaxEntries
            Me._NewLast = NewLast
            If NewLast Then
                Dim foo(MaxEntries - 1) As T
                Me._List.AddRange(foo)
            End If
        End Sub

        Public Sub Add(item As T)
            If Me._NewLast Then
                Me._List(Me._pos) = item
                Me._pos += 1
                If Me._pos = Me._max Then
                    Me._pos = 0
                End If
            Else
                Me._List.Insert(0, item)
                If Me._List.Count = Me._max + 1 Then
                    Me._List.RemoveAt(Me._max)
                End If
            End If
        End Sub

        Public Function TheList() As List(Of T)
            Return Me._List
        End Function
    End Class

Test Code

        Debug.WriteLine("---------- Circular List ----------------")
        Debug.WriteLine("-------TEST1 step by step - keep 4 newest")
        Dim TEST1 As New ListLimit(Of String)(4, False)
        Dim N As DateTime = DateTime.Now
        Dim EndDT As DateTime = N.AddSeconds(11)
        Do
            TEST1.Add(N.ToString("HH:mm:ss"))
            Debug.WriteLine("Add " & N.ToString("HH:mm:ss") & " -------")
            For Each li As String In TEST1.TheList
                If li IsNot Nothing Then Debug.WriteLine(li)
            Next
            Threading.Thread.Sleep(999)
            N = DateTime.Now
        Loop While N < EndDT

        Debug.WriteLine("")
        Debug.WriteLine("-------TEST2 step by step - keep 4 oldest")
        Dim TEST2 As New ListLimit(Of String)(4)
        N = DateTime.Now
        EndDT = N.AddSeconds(11)
        Do
            TEST2.Add(N.ToString("HH:mm:ss"))
            Debug.WriteLine("Add " & N.ToString("HH:mm:ss") & " -------")
            For Each li As String In TEST2.TheList
                If li IsNot Nothing Then Debug.WriteLine(li)
            Next
            Threading.Thread.Sleep(999)
            N = DateTime.Now
        Loop While N < EndDT

Results

**---------- Circular List ----------------
-------TEST1 step by step - keep 4 newest
Add 14:06:02 -------
14:06:02
Add 14:06:03 -------
14:06:03
14:06:02
Add 14:06:04 -------
14:06:04
14:06:03
14:06:02
Add 14:06:05 -------
14:06:05
14:06:04
14:06:03
14:06:02
Add 14:06:06 -------
14:06:06
14:06:05
14:06:04
14:06:03
Add 14:06:07 -------
14:06:07
14:06:06
14:06:05
14:06:04
Add 14:06:08 -------
14:06:08
14:06:07
14:06:06
14:06:05
Add 14:06:09 -------
14:06:09
14:06:08
14:06:07
14:06:06
Add 14:06:10 -------
14:06:10
14:06:09
14:06:08
14:06:07
Add 14:06:11 -------
14:06:11
14:06:10
14:06:09
14:06:08
Add 14:06:12 -------
14:06:12
14:06:11
14:06:10
14:06:09

-------TEST2 step by step - keep 4 oldest
Add 14:06:13 -------
14:06:13
Add 14:06:14 -------
14:06:13
14:06:14
Add 14:06:15 -------
14:06:13
14:06:14
14:06:15
Add 14:06:16 -------
14:06:13
14:06:14
14:06:15
14:06:16
Add 14:06:17 -------
14:06:17
14:06:14
14:06:15
14:06:16
Add 14:06:18 -------
14:06:17
14:06:18
14:06:15
14:06:16
Add 14:06:19 -------
14:06:17
14:06:18
14:06:19
14:06:16
Add 14:06:20 -------
14:06:17
14:06:18
14:06:19
14:06:20
Add 14:06:21 -------
14:06:21
14:06:18
14:06:19
14:06:20
Add 14:06:22 -------
14:06:21
14:06:22
14:06:19
14:06:20
Add 14:06:23 -------
14:06:21
14:06:22
14:06:23
14:06:20**