'_________________________________________________________________________________

'                            S T R E A M   R E A D E R   /   W R I T E R   D E M O
'                                                   Created 11/9/06
'                                                       Ron Kessler
'                                                   C# 2005 Version
'_________________________________________________________________________________

'Last updated 11/9/06

'FEATURES: 
'   1.  Shows how to read/write to a sequential text file
'   2.  Lets user create file when program first loads
'   3.  Items can be added/removed from list box
'   4.  Items in list box can be saved to disk
'   5.  Shows how to use For-Each loop with list box items
'   6.  Uses structured error handling and the Using Structure block to close the readers automatically!

Imports System.IO



Public Class frmMain

    Dim diskFile As String = "..\..\inventory.txt"       'our datafile  remember to include the ..\ bit!


    '---this next flag variable keeps them from loading LB more than once. Is set in DoReload and
    'reset in btnClear_Click
    Dim listBoxAlreadyLoaded As Boolean = False


    Private Sub frmMain_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        '---fill the list box from file
        DoReload()
    End Sub

    Private Sub btnReload_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnReload.Click

        DoReload()

    End Sub


    Private Sub DoReload()

        If listBoxAlreadyLoaded Then Exit Sub 'keeps them from duplicating stuff

        '---define our scratch variables here
        Dim dataFromFile As String = ""       'holds the line of text from the file

        '---if file does not exist lets create it for them if they want to.
        If File.Exists(diskFile) = False Then
            If MessageBox.Show _
            ("Cannot locate the inventory file" & Err.Description & "Create It?", _
            "Ron's Train Store", MessageBoxButtons.YesNo, MessageBoxIcon.Error) = _
            Windows.Forms.DialogResult.Yes Then

                File.Create(diskFile)
            Else
                Me.Close()
            End If
        Else


            Try
                Using myReader = New StreamReader(diskFile)   'this will close/dispose of reader automatically

                    Do Until myReader.EndOfStream                  'or Do Until dataFromFile Is Nothing
                        dataFromFile = myReader.ReadLine
                        lstItems.Items.Add(dataFromFile)
                    Loop
                End Using

                listBoxAlreadyLoaded = True        'keeps them from duplicating items

            Catch ex As IOException
                MsgBox("An error occurred while reading...." & Err.Description, MsgBoxStyle.Critical)
                Me.Close()

            End Try
        End If


    End Sub

    Private Sub btnSave_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSave.Click

        Dim lbItem As String = ""

        Try
            '---if file does not exist, the SW will create it
            Using myWriter = New StreamWriter(diskFile, False)    'false= do not append   True= append

                '---now cycle through the items in the listbox and save them to disk
                For Each lbItem In lstItems.Items
                    myWriter.WriteLine(lbItem)
                Next

            End Using

            MsgBox("Your data has been updated", MsgBoxStyle.Information, "Ron's Train Hut")

        Catch ex As IOException
            MsgBox("An error occurred while saving your data...." & Err.Description, MsgBoxStyle.Critical)
            Me.Close()
        End Try


    End Sub

  

    Private Sub btnAdd_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAdd.Click
        '---add new item
        Dim myNewItem As String = txtNewItem.Text.ToString.Trim
        lstItems.Items.Add(myNewItem)
    End Sub


    Private Sub btnClear_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnClear.Click
        '---clear listbox and reset flag so they can read file again
        lstItems.Items.Clear()
        listBoxAlreadyLoaded = False
    End Sub

    Private Sub btnDelete_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnDelete.Click

        '---if they selected an item then SelectedIndex =>0 so if it is -1 they didn't select one to delete yet!
        If lstItems.SelectedIndex <> -1 Then
            lstItems.Items.Remove(lstItems.SelectedItem)
        End If
    End Sub

    Private Sub btnExit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnExit.Click
        Me.Close()
    End Sub
End Class