Bound Listbox turns items invisible on data refresh. Why? - vb.net

Question

I have a list box bound to a list is a class. All works fine until I try to add a new item to the list. during this process the data source is set to nothing to refresh the list and apparently 'Refresh' doesn't do it. The list gets refreshed and the other controls bound to the listboxes data show that the list is there and is correct however the list appears empty although it does show scroll bars. I have tried to change the font color, just in case.. Nothing!
Does someone know why this happens? how to fix it? Or a better way to refresh?
Code:
Private Sub btnNew_Click(sender As Object, e As EventArgs) Handles btnNew.Click
'lbNames is the listbox carrying all the data
Dim oContacts As List(Of clsContact) = lbNames.DataSource
lbNames.DataSource = Nothing
'Build the new Item, add it to the collection
Dim oNewCont As New clsContact
oNewCont.Editable = True
oNewCont.IsActive = True
oNewCont.Firstname = "Jimmy"
oNewCont.Lastname = "Smith"
oContacts.Add(oNewCont)
lbNames.Refresh()
' Re-Set up Autocomplete text box
Dim MySource As New AutoCompleteStringCollection()
For Each oc As clsContact In oContacts
MySource.Add(oc.FullName)
Next
txtName.AutoCompleteMode = AutoCompleteMode.Suggest
txtName.AutoCompleteCustomSource = MySource
txtName.AutoCompleteSource = AutoCompleteSource.CustomSource
'Set List Box data back to the collection
lbNames.DataSource = oContacts
lbNames.DisplayMember = "FullName"
End Sub
The starting LOAD:
Private Sub frmMain_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Dim oCont As List(Of clsContact)
lbNames.DrawMode = DrawMode.OwnerDrawVariable
Dim oTypes As List(Of clsPhoneType) = loadTypes()
cboPhoneType.DataSource = oTypes
cboPhoneType.DisplayMember = "Type"
cboPhoneType.ValueMember = "ID"
oCont = LoadNames()
lbNames.DataSource = oCont
lbNames.DisplayMember = "FullName"
Dim MySource As New AutoCompleteStringCollection()
For Each oc As clsContact In oCont
MySource.Add(oc.FullName)
Next
txtName.AutoCompleteMode = AutoCompleteMode.Suggest
txtName.AutoCompleteCustomSource = MySource
txtName.AutoCompleteSource = AutoCompleteSource.CustomSource
End Sub
Private Sub lbNames_DrawItem(ByVal sender As Object, ByVal e As System.Windows.Forms.DrawItemEventArgs) Handles lbNames.DrawItem
e.DrawBackground()
Dim textBrush As Brush = Brushes.Black
Dim drawFont As System.Drawing.Font = e.Font
If (e.State And DrawItemState.Selected) = DrawItemState.Selected Then
e.Graphics.FillRectangle(Brushes.WhiteSmoke, e.Bounds)
End If
Dim oCont As clsContact = DirectCast(sender, System.Windows.Forms.ListBox).Items(e.Index)
If oCont.IsActive Then
textBrush = Brushes.Black
If oCont.IsDirty Then textBrush = Brushes.LightCoral
Else
textBrush = Brushes.LightGray
End If
Dim str = oCont.FullName
e.Graphics.DrawString(str, e.Font, textBrush, e.Bounds, StringFormat.GenericDefault)
e.DrawFocusRectangle()
End Sub

Answer 1

You're using the wrong tools. The List(Of T) doesn't raise any events whatsoever. When bound to a control, the control doesn't know if any items are added/removed/moved. Luckily, the BindingList(Of T) comes to rescue. It will raise a ListChanged event whenever the list is modified. As a bonus, if your class/model implements the INotifyPropertyChanged interface, the control will also reflect property changes.
lbNames.DataSource = New BindingList(Of clsContact)(oCont)
Here's a sample form to show you the basics:
Imports System.ComponentModel
Public Class Form1
Public Sub New()
Me.InitializeComponent()
Me.btnAdd = New Button With {.TabIndex = 0, .Dock = DockStyle.Top, .Height = 30, .Text = "Add new contact"}
Me.btnChange = New Button With {.TabIndex = 1, .Dock = DockStyle.Top, .Height = 30, .Text = "Change random contact name"}
Me.lbContacts = New ListBox With {.TabIndex = 2, .Dock = DockStyle.Fill}
Me.Controls.AddRange({Me.lbContacts, Me.btnChange, Me.btnAdd})
End Sub
Private Sub HandleMeLoad(sender As Object, e As EventArgs) Handles Me.Load
Dim list As New List(Of Contact)
For i As Integer = 1 To 10
list.Add(New Contact With {.Name = String.Format("Contact # {0}", i)})
Next
Me.lbContacts.DataSource = New BindingList(Of Contact)(list)
Me.lbContacts.DisplayMember = "Name"
End Sub
Private Sub HandleButtonAddClick(sender As Object, e As EventArgs) Handles btnAdd.Click
Dim list As BindingList(Of Contact) = DirectCast(Me.lbContacts.DataSource, BindingList(Of Contact))
list.Add(New Contact With {.Name = String.Format("Contact # {0}", (list.Count + 1))})
End Sub
Private Sub HandleButtonChangeClick(sender As Object, e As EventArgs) Handles btnChange.Click
Static rnd As New Random()
Dim list As BindingList(Of Contact) = DirectCast(Me.lbContacts.DataSource, BindingList(Of Contact))
If (list.Count > 0) Then
With list.Item(rnd.Next(0, list.Count))
.Name = Guid.NewGuid().ToString()
End With
End If
End Sub
Public Class Contact
Implements INotifyPropertyChanged
Public Event PropertyChanged As PropertyChangedEventHandler Implements System.ComponentModel.INotifyPropertyChanged.PropertyChanged
Public Property Name As String
Get
Return Me.m_name
End Get
Set(value As String)
If (value <> Me.m_name) Then
Me.m_name = value
RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs("Name"))
End If
End Set
End Property
Private m_name As String
End Class
Private WithEvents btnAdd As Button
Private WithEvents btnChange As Button
Private WithEvents lbContacts As ListBox
End Class

Answer 2

It seems that the solution to fixing this problem is to flip the drawmode back to normal.
adding:
lbNames.DrawMode = DrawMode.Normal
lbNames.DrawMode = DrawMode.OwnerDrawVariable
Fixes the problem.
I guess what is happening is that the drawing handler is becoming disconnected for some reason so the contests of the list are not redrawn when the data source is attached.
My new working code:
Private Sub btnNew_Click(sender As Object, e As EventArgs) Handles btnNew.Click
'lbNames is the listbox carrying all the data
Dim oContacts As List(Of clsContact) = lbNames.DataSource
lbNames.DataSource = Nothing
'Build the new Item, add it to the collection
Dim oNewCont As New clsContact
oNewCont.Editable = True
oNewCont.IsActive = True
oNewCont.Firstname = "Jimmy"
oNewCont.Lastname = "Smith"
oContacts.Add(oNewCont)
' Re-Set up Autocomplete text box
Dim MySource As New AutoCompleteStringCollection()
For Each oc As clsContact In oContacts
MySource.Add(oc.FullName)
Next
txtName.AutoCompleteMode = AutoCompleteMode.Suggest
txtName.AutoCompleteCustomSource = MySource
txtName.AutoCompleteSource = AutoCompleteSource.CustomSource
'Set List Box data back to the collection
lbNames.DataSource = oContacts
lbNames.DisplayMember = "FullName"
lbNames.DrawMode = DrawMode.Normal
lbNames.DrawMode = DrawMode.OwnerDrawVariable
End Sub