Mastering Visual Basic .NET

method, so we must provide our own ToString method that describes each contact. The company
name should be adequate, but if there are two companies by the same name, you can use another
field to differentiate them. I’ve used the contact name, but you can use any of the other properties
(the URL would be a good choice).
Each contact is stored in a variable of the Contact type and added to the ListBox control. Now,
we must change the code of the main form a little. First, remove the navigational buttons; we no
longer need them. Their function will be replaced by a few lines of code in the ListBox control’s
SelectedIndexChanged event. Every time the user selects another item on the list, the statements
shown in Listing 8.29 display the contact’s properties on the various TextBox controls on the form.
Listing 8.29: Displaying the Fields of the Selected Contact Object
Private Sub ListBox1_SelectedIndexChanged(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles ListBox1.SelectedIndexChanged
currentContact = ListBox1.SelectedIndex
ShowContact()
End Sub
The ShowContact() subroutine reads the object stored at the location specified by the current-
Contact variable and displays its properties on the various TextBox controls on the form.
When a new contact is added, the code creates a new Contact object and adds it to the ListBox control.
When a contact is edited, a new Contact object replaces the currently selected object on the control.
The code is very similar to the code of the Contacts application. I should mention that the ListBox
control is locked while a contact is being added or edited, because it doesn’t make sense to select
another contact at that time. Besides, we want to be able to replace the contact being edited when the
user is done.
To delete a contact (Listing 8.30), we simply remove the currently selected object on the control.
In addition, we must select the next object, or the first object if the deleted object was the last
one in the list.
Listing 8.30: Deleting an Object on the ListBox
Private Sub bttnDelete_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles bttnDelete.Click
If currentContact > -1 Then
ListBox1.Items.RemoveAt(currentContact)
If currentContact = ListBox1.Items.Count Then _
currentContact = ListBox1.Items.Count - 1
If currentContact = -1 Then
ClearFields()
MsgBox(“There are no more contacts”)
Else
ShowContact()
End If
A “REAL” CLASS
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