Create a undo/redo textboxes algorithm in VB.Net - vb.net

Question

I would love to create a type algorithm Undo/Redo in VB.Net, first at least i want to make the undo.
if we have the example Textbox1.Text = a,b,c
then change to = a,b,c,e
then change to = a,b,c,f
when I click on undo I want to display (that is, the value before it. before after a,b, c, f, was a, b, c,e
a,b,c,e
and when I click once again I want to display
a,b,c
that is, an undo / redo algorithm of added values
I first created a global list.
Public Module Globals
Public Undo As New List(Of String)
End Module
if Textboxes value is not exists in the list, then I will add it.
Private Sub Button1(sender As Object, e As EventArgs) Handles Button1.Click
If Undo IsNot TextBox1.Text Then
Undo.Add(TextBox1.Text)
End If
End Sub
hey well here's the tricky part
Private Sub Undo_Click(sender As Object, e As EventArgs) Handles Undo.Click
Dim i as integer = Undo.Count
While TextBox1.Text IsNot Undo(i)
TextBox1.Text = Undo(i)
End While
End Sub
For i As Integer = Undo.Count To 0 Step -1
TextBox1.Text = Undo(i)
Next
unfortunately no such loop works in this case.

Answer 1

Try this:
Private Undos As List(Of String) = New List(Of String)()
Private AddUndo As Boolean = True
Private Sub textBox1_TextChanged(ByVal sender As Object, ByVal e As EventArgs)
If AddUndo = True Then
Undos.Add(textBox1.Text)
End If
End Sub
Private Sub button1_Click(ByVal sender As Object, ByVal e As EventArgs)
If Undos.Count <> 0 Then
AddUndo = False
If Undos.Count > 1 Then
textBox1.Text = Undos(Undos.Count - 2)
Undos.RemoveAt(Undos.Count - 1)
Else
textBox1.Text = ""
Undos.RemoveAt(0)
End If
AddUndo = True
End If
End Sub