Question

I have this problem with late binding: I am creating a grocery list application. I have a class named Item which stores the name, price, quantity, and description of an item on the grocery list.

I have a module named ListCollection which defines a Collection of Item objects. I have created an Edit form which will automatically display the currently selected ListCollection item properties, but whenever I attempt to fill the text boxes, it tells me that Option Strict disallows late binding.

I COULD take the easy route and disable Option Strict, but I’d prefer to figure out what the problem is so I know for future reference.

I shall paste pertinent code here. (Late binding error is in EditItem.vb.)

Item.vb code:

' Member variables:
Private strName As String

' Constructor
Public Sub New()
    strName = ""

' Name property procedure
Public Property Name() As String
    Get
        Return strName
    End Get
    Set(ByVal value As String)
        strName = value
    End Set
End Property

ListCollection.vb code:

' Create public variables.
Public g_selectedItem As Integer ' Stores the currently selected collection item.

' Create a collection to hold the information for each entry.
Public listCollection As New Collection

' Create a function to simplify adding an item to the collection.
Public Sub AddName(ByVal name As Item)
    Try
        listCollection.Add(name, name.Name)
    Catch ex As Exception
        MessageBox.Show(ex.Message)
    End Try
End Sub

EditItem.vb code:

Private Sub EditItem_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

    ' Set the fields to the values of the currently selected ListCollection item.
    txtName.Text = ListCollection.listCollection(g_selectedItem).Name.Get ' THIS LINE HAS THE ERROR!

I have tried declaring a String variable and assigning the Item property to that, and I have also tried grabbing the value directly from the List item (not using the Get function), and neither of these made a difference.

How can I fix this problem?

Answer 1

You must cast the item from “Object” to your type (“EditItem”).

http://www.codeproject.com/KB/dotnet/CheatSheetCastingNET.aspx

EDIT:

Private Sub EditItem_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

    ' getting the selected item
    Dim selectedItem As Object = ListCollection.listCollection(g_selectedItem)

    ' casting the selected item to required type
    Dim editItem As EditItem = CType(selectedItem, EditItem)

    ' setting value to the textbox
    txtName.Text = editItem.Name

I didn’t code anything in VB.NET for years, I hope it is all right.