Writing to files, adding to collections

[steph573]

Hi,

I have been having issues with my application. Basically, I am reading a file, saving it into a collection. Then, modifying the collection, and having the option to save the changes back into the file.

I chose to open the file at form load, read each line and save each into the collection's property, and have the collection key value displayed in the list box. I can then, select the key value, and have each collection property displayed in labels on the form. Also, I am to either add new items, or update existing ones. I am currently having trouble, displaying the items (stored in the collection properties) added, but also previously there, when I select their key value from the list box. I have an inventory number serving as a key, and a description, a cost price, a retail price, and onhand counts displayed in labels. Every time that I select an item from the list box I get the following error:

argument 'index' is not a valid value

I have trouble figuring out what is going on.

I have:
a separate collection declaration, a separate class declaration with inventory properties.

a main form displaying the list box, with labels, and also buttons to either display, add, or update the collection. With of course, the option, to save data back into the file.

Imports System.IO

Public Class frmMain

    Private Sub frmMain_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim objInventory As New Inventory
        Dim inventoryFile As StreamReader

        Try
            'Open the file.
            inventoryFile = File.OpenText("Inventory.txt")

            'Enter loop and read till end of file.
            Do Until inventoryFile.Peek = -1

                'Read lines from file, save into Inventory object properties.
                objInventory.InvNumber = inventoryFile.ReadLine
                objInventory.Description = inventoryFile.ReadLine
                objInventory.Cost = inventoryFile.ReadLine
                objInventory.Retail = inventoryFile.ReadLine
                objInventory.OnHand = inventoryFile.ReadLine

                'Display inventory number in list box.
                lstInventory.Items.Add(objInventory.InvNumber)
            Loop

            'Close the file.
            inventoryFile.Close()
        Catch
            'Display error message.
            MessageBox.Show("The file cannot be opened")
        End Try
    End Sub
 

    Private Sub lstInventory_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles lstInventory.SelectedIndexChanged
     
    End Sub

    Private Sub mnuFileExit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles mnuFileExit.Click
        'Close the form.
        Me.Close()
    End Sub
    Private Sub btnAddInventory_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAddInventory.Click
        'Create an instance of the frmAdd form.
        Dim addForm As New frmAdd

        'Display the form.
        addForm.ShowDialog()
    End Sub
    Private Sub btnDisplay_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnDisplay.Click
        'Create an Inventory object
        'Create an Inventory object
        Dim objInventory As Inventory

        'Determine if item is selected.
        If lstInventory.SelectedIndex <> -1 Then

            'Retrieve student's data from inventoryCollection. Convert object into Inventory object.
            Try

                objInventory = CType(inventoryCollection.Item(lstInventory.SelectedItem), Inventory)

                'Display data in labels data stored in inventory object.
                DisplayInput(objInventory)
            Catch ex As Exception
                'Display error message.
                MessageBox.Show(ex.Message)
            End Try
        End If
    End Sub
    Private Sub DisplayInput(ByVal objInventory As Inventory)
        Dim sngCost As Single
        Dim sngRetail As Single

        lblDisplayInvNum.Text = objInventory.InvNumber.ToString
        lblDisplayDescription.Text = objInventory.Description
        lblDisplayOnHand.Text = objInventory.OnHand.ToString

        sngCost = CSng(objInventory.Cost)
        sngRetail = CSng(objInventory.Retail)

        lblDisplayCost.Text = sngCost.ToString("c")
        lblDisplayRetail.Text = sngRetail.ToString("c")
    End Sub

    Private Sub btnUpdate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnUpdate.Click
        'Create an instance of the frmAdd form.
        Dim updateForm As New frmUpdate

        'Display the form.
        updateForm.ShowDialog()
    End Sub
    Private Sub UpdateListBox()
        'Clear the list box
        lstInventory.Items.Clear()

        Dim objInventory As Inventory
        For Each objInventory In inventoryCollection
            lstInventory.Items.Add(objInventory.invNumber)
        Next

        'Select first item in list
        If lstInventory.Items.Count > 0 Then
            lstInventory.SelectedIndex = 0
        Else
            lblInvNumber.Text = String.Empty
            lblDescription.Text = String.Empty
            lblCost.Text = String.Empty
            lblRetail.Text = String.Empty
            lblOnHand.Text = String.Empty
        End If
    End Sub
End Class

I use my add form to load data from my text boxes into my object parameter, display the inventory collection key in my main form list box, and have the option to save data back into the file

Imports System.IO

Public Class frmAdd
    Private Sub frmAdd_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        'Set focus.
        txtInvNumber.Focus()
    End Sub
    Private Sub InputData(ByVal objInventory As Inventory)
        'InputData procedures gets data from form and stores it
        'objInventory object parameter.
        objInventory.InvNumber = txtInvNumber.Text
        objInventory.Description = txtDescription.Text
        objInventory.Cost = CSng(txtCost.Text)
        objInventory.Retail = CSng(txtRetail.Text)
        objInventory.OnHand = CInt(txtOnHand.Text)
    End Sub

    Private Sub btnDisplay_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnClose.Click
        'Close the form.
        Me.Close()
    End Sub

    Private Sub btnAddtoForm_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAddtoForm.Click
        'Create instance of Inventory class.
        Dim newInventory As New Inventory

        'Get input data from form.
        InputData(newInventory)

        'Display inventory number.
        frmMain.lstInventory.Items.Add(newInventory.InvNumber)

        'Save inventory object to inventoryCollection.
        AddRecord(newInventory)

        'Check for check box selection.
        If chkSaveCollection.Checked = True Then
            Dim writeFile As StreamWriter
            Dim sngCost As Single
            Dim sngRetail As Single

            sngCost = CSng(newInventory.Cost)
            sngRetail = CSng(newInventory.Retail)

            Try
                'Open the file in Append mode.
                writeFile = File.AppendText("Inventory.txt")

                'Write to file.
                writeFile.WriteLine(newInventory.InvNumber)
                writeFile.WriteLine(newInventory.Description)
                writeFile.WriteLine(newInventory.Cost)
                writeFile.WriteLine(newInventory.Retail)
                writeFile.WriteLine(newInventory.OnHand)

                'Close StreamWriter.
                writeFile.Close()
            Catch ex As Exception
                'Display error message
                MessageBox.Show(ex.Message)
            End Try
        End If
        'Return focus.
        txtInvNumber.Focus()
    End Sub
End Class

Can anyone help?

[jmcilhinney]

You're not actually keeping any of the data you read except the inventory number. Here's what you should do:

1. Create a BindingList(Of Inventory).
2. As you read the file, create a New Inventory object each iteration of the loop, set its properties and then Add it to the list.
3. Bind the list to the ListBox by setting the DisplayMember, ValueMember and DataSource of the ListBox.
4. Bind the list to the Labels as well so that they update automatically when the user makes a selection.
5. To get the current item, use the SelectedItem property of the ListBox.
6. When you update an existing item, call the ResetItem method of the BindingList and use the SelectedIndex of the ListBox as the position.
7. When you add a new item, call the ResetBindings method of the BindingList.

I would also strongly recommend not storing one record on multiple lines. I'd recommend one record per record and delimiting use commas or Tabs or something else if you have a good reason for it.

[steph573]

You're not actually keeping any of the data you read except the inventory number. Here's what you should do:

1. Create a BindingList(Of Inventory).
2. As you read the file, create a New Inventory object each iteration of the loop, set its properties and then Add it to the list.
3. Bind the list to the ListBox by setting the DisplayMember, ValueMember and DataSource of the ListBox.
4. Bind the list to the Labels as well so that they update automatically when the user makes a selection.
5. To get the current item, use the SelectedItem property of the ListBox.
6. When you update an existing item, call the ResetItem method of the BindingList and use the SelectedIndex of the ListBox as the position.
7. When you add a new item, call the ResetBindings method of the BindingList.

I would also strongly recommend not storing one record on multiple lines. I'd recommend one record per record and delimiting use commas or Tabs or something else if you have a good reason for it.

Am I basically creating a dataset and using the file as a data source?