How to choose with List in VB

Provide
Single Item function:
Cmddel_click
Cmdadd_click
Multiple Item Function:
Cmddelall_click
Cmdaddall_click
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' Option Explicit

' Author:nyb
' Time:2002-04-05
' Incoming list1,list2, and then we can handle the item in List1, and List2.
' *all areas of code where modifications are necessary
' *to integrate this object with a project are documented
' With comments denoted by:.
' *to locate these comments,search for ' *note::.
'****************************************************************************************

Public Sub Cmddelall_click (List1 as ListBox, List2 as ListBox) ' <<
' *purpose:delete all List2.item
' *accept:list1 no use, List2 processing object
For i = (list2.listcount-1) to 0 Step-1
List2.removeitem I
Next I
End Sub
Public Sub Cmdadd2to1_click (List1 as ListBox, List2 as ListBox, List3 as ListBox) ' >>
' *purpose:all item of List1 and List2 are inputed to List3
' *accept:list1,list2
For i = 0 to (list1.listcount-1)
List3.additem List1.list (i)
Next I
For i = 0 to (list2.listcount-1)
List3.additem List2.list (i)
Next I
End Sub

Public Sub Cmdaddall_click (List1 as ListBox, List2 as ListBox, Index as Integer) ' >>
' *purpose:add all item of List1 inputed to List2.if item had been there, It won ' t be inputed
' *accept:list1,list2
If list2.listcount = 0 Then
For i = 0 to (list1.listcount-1)
List2.additem List1.list (i)
Next I
Else
For i = 0 to (list1.listcount-1)
Flag = checkselected (List1, List2, List1.list (i))
If Flag = "Notbe" Then list2.additem list1.list (i)
Next I
End If
End Sub


Public Sub Cmddel_click (List1 as ListBox, List2 as ListBox) ' <---
' *purpose:the selected items of List2 are cleared
' *accept:list1 no use, List2 processing object
Dim I as Integer
If list2.selcount > 0 Then
For i = (list2.listcount-1) to 0 Step-1
If list2.selected (i) = True Then List2.removeitem i
Next I
End If
End Sub

Public Sub Cmdadd_click (List1 as ListBox, List2 as ListBox, Index as Integer) '--->
' *purpose:the selected items of List1 is inputed into List2
' List2 is empty, List2 can be selected more, then items selected in List1 are inputed to List2
' List2 is not empty, list2 can choose more, then check whether the item is in List2, if in, then don't add into List2
' List2 is set to a single selection, then List2 only add the first selected item in List1
' *accept:list1 selected items, List2 for the listbox to join
Dim I as Integer
Dim Flag as String

If Index > 0 Then
If list2.listcount >= 1 Then
If Index = 2 Then
If List2.listcount >= 2 Then
If list1.multiselect = 0 Then
MsgBox "can only select two phase contrast!" ", vbexclamation," Operation Tips! "
Exit Sub
End If
End If
End If
End If
End If

If list2.listcount = 0 and list2.multiselect = 2 Then
For i = 0 to (list1.listcount-1)
If list1.selected (i) = True Then list2.additem list1.list (i)
Next I
ElseIf list2.listcount > 0 and list2.multiselect = 2 Then
For i = 0 to (list1.listcount-1)
Flag = checkselected (List1, List2, List1.list (i))
If list1.selected (i) = True and Flag = "notbe" Then list2.additem list1.list (i)
Next I
ElseIf list2.multiselect = 0 Then
Call Cmddelall_click (List1, List2)
For i = 0 to (list1.listcount-1)
If list1.selected (i) = True Then list2.additem list1.list (i)
Next I
End If
Call Clearselect (LIST1)
End Sub

Private Function checkselected (List1 as ListBox, List2 as ListBox, Cityitem as String) as String
' *purpose: ' Check if item has been added, add checkselected = ' be '
' *accept:list1 selected items, List2 for the Listbox,cityitem to be added as a selected item in List1
' *feedback:checkselected, ' be ' indicates that this item exists in the List2
For i = (list2.listcount-1) to 0 Step-1
If Cityitem = list2.list (i) Then
checkselected = "Be"
Exit for
else:checkselected = "Notbe"
End If
Next I
End Function

Private Sub Clearselect (List1)
' *purpose:clear List1 ' s selected
' *accept:list1, the list box to clear selected
For i = 0 to List1.listcount-1
If list1.selected (i) = True Then
list1.selected (i) = False
End If
Next I
End Sub