Design a form in VB with two List boxes. Set the style property of both to 0 and 2 (Multi select) respectively. One with the left arrow and one with the right arrow. On pressing the left arrow the selected item from List Box 1 should be transferred to List Box 2 (only if it does exist in List Box 2). If the right arrow is pressed, the selected item (multiple selection are not in ListBox2) transferred to List box 1.Add items and remove items buttons for each list. Duplicate item should not be added.

file.vb

  
Private Sub cmdAddLeft_Click()  
    List1.AddItem (inputBox("Enter Item"))  
End Sub  
  
Private Sub cmdAddRight_Click()  
    Item = inputBox("Enter Item: ", "Left List")  
    For i = 0 TolstRight.ListCount - 1  
        If lstRight.List(i) = Item Then  
            MsgBox "Record Is Already Present In The List.", vbOKOnly, "Result"  
            Exit Sub  
        End If  
        lstRight.AddItem Item  
    Next  
End Sub  
  
Private Sub cmdRemoveLeft_Click()  
    If lstRight.ListCount = 0 Then  
        MsgBox ("No more items to delete")  
        End  
    Else  
        lstRight.RemoveItem (0)  
          
    End If  
End Sub  
Private Sub cmdRemoveRight_Click()  
    If List1.ListCount = 0 Then  
        MsgBox ("No more items to delete")  
        End  
    Else  
        List1.RemoveItem (0)  
    End If  
      
End Sub  
  
Private Sub Command1_Click()  
    cnt = lstRight.ListCount  
      
    If List1.ListCount = 0 Then  
        MsgBox ("No more items to Move")  
        Exit Sub  
    Else  
        For i = List1.ListCount - 1 To 0 Step -1  
            If List1.Selected(i) = True Then  
                For j = lstRight.ListCount - 1 To 0 Step -1  
                    If lstRight.List(j) <> List1.List(i) Then  
                        lstRight.AddItem (List1.List(i))  
                        List1.RemoveItem (i)  
                    Else  
                        MsgBox ("Item "& List1.Selected(i) & "already exist")  
                    End If  
                      
                Next  
                  
            End If  
        Next  
          
    End If  
      
End Sub  
  
Private Sub Command2_Click()  
    If List2.ListCount = 0 Then  
        MsgBox ("No more items to Move")  
        Exit Sub  
          
    Else  
        List1.AddItem (List2.List(ListIndex))  
        List2.RemoveItem (ListIndex)  
    End If  
End Sub