We will use a global variable changed that is Boolean. Intitially, we will set it to false. We will change the value under the following conditions:

• When we add to the list box: changed=True
• When we delete from the list box: changed=True
• When we save or save as a file: changed=False

We must check to see if there are any changes when we:

• Select New
• Select open
• Select Exit
• Close the program with the X in the top right corner.

Add the variable changed to the global variables:

Public Class Form1
    Dim currentFile As String
    Dim Changed As Boolean = False

Because we will ask if they want to save from more than one place (when we remind them to save) we have written asktosave as a general function. That is, it is not a procedure that receives some event arguments as its parameters. It must be a function so that it can return that information to the calling procedure.

Code for AskToSave

Private Function AskToSave() As Boolean
   Dim Answer As MsgBoxResult
   Dim okToClear As Boolean = False 'will be the return value
   If Changed Then
      Answer = MsgBox("Do you want to save?", _
      MsgBoxStyle.YesNoCancel + MsgBoxStyle.Question, "Save")
      If Answer = MsgBoxResult.Yes Then
         SaveList() 
         okToClear = True
      End If
      If Answer = MsgBoxResult.No Then
         okToClear = True 'clear the list box without saving
      End If
      If Answer = MsgBoxResult.Cancel Then
         okToClear = False
      End If
   End If
   'if changed is false, then false is returned
   Return okToClear
 End Function 'AskToSave

NEXT: Build the Menu