Imports System.Windows.Interactivity
Imports System.Collections.Specialized

Public Class ScrollIntoViewForListBox
   Inherits Behavior(Of ListBox)

   Private ItemsSource As INotifyCollectionChanged

   Private ListControl As ListBox

   ''' <summary>
   '''  When Beahvior is attached
   ''' </summary>
   Protected Overrides Sub OnAttached()
      MyBase.OnAttached()
      ListControl = Me.AssociatedObject
      AddHandler Me.AssociatedObject.SelectionChanged, AddressOf AssociatedObject_SelectionChanged
   End Sub


   Private Sub AssociatedObject_CollectionChanged(sender As Object, e As System.Collections.Specialized.NotifyCollectionChangedEventArgs)
      If ListControl.SelectedItem IsNot Nothing Then
         Dim SelectedItemIndex As Integer = ListControl.Items.IndexOf(ListControl.SelectedItem)
         ListControl.Dispatcher.BeginInvoke(DirectCast(Sub()
                                                          ListControl.UpdateLayout()
                                                          If ListControl.SelectedItem IsNot Nothing Then
                                                             ListControl.ScrollIntoView(ListControl.SelectedItem)
                                                          End If
                                                       End Sub, Action))
         If SelectedItemIndex > 0 Then
            ListControl.Dispatcher.BeginInvoke(DirectCast(Sub()
                                                             ListControl.UpdateLayout()
                                                             ListControl.ScrollIntoView(ListControl.Items(SelectedItemIndex - 1))
                                                          End Sub, Action))
         End If
         If SelectedItemIndex < ListControl.Items.Count - 2 Then
            ListControl.Dispatcher.BeginInvoke(DirectCast(Sub()
                                                             ListControl.UpdateLayout()
                                                             ListControl.ScrollIntoView(ListControl.Items(SelectedItemIndex + 1))
                                                          End Sub, Action))
         End If
      End If
   End Sub

   ''' <summary>
   ''' On Selection Changed
   ''' </summary>
   ''' <param name="sender"></param>
   ''' <param name="e"></param>
   Private Sub AssociatedObject_SelectionChanged(sender As Object, e As SelectionChangedEventArgs)
      If IsNothing(ItemsSource) Then
         Dim CurrItemsSource As IEnumerable = Me.AssociatedObject.ItemsSource
         ItemsSource = TryCast(CurrItemsSource, INotifyCollectionChanged)
         AddHandler ItemsSource.CollectionChanged, AddressOf AssociatedObject_CollectionChanged
         RemoveHandler Me.AssociatedObject.SelectionChanged, AddressOf AssociatedObject_SelectionChanged

         ' SE SI CAMBIA ITEMSSOURCE PERDE IL RIFERIMENTO E SMETTE DI FUNZIONARE
         ' PER RIATTIVARLO USARE IL SEGUENTE CODICE COMMENTATO
         'ElseIf ItemsSource IsNot Me.AssociatedObject.ItemsSource Then
         '   Dim PreviousItemsSourceList As INotifyCollectionChanged = TryCast(ItemsSource, INotifyCollectionChanged)
         '   RemoveHandler PreviousItemsSourceList.CollectionChanged, AddressOf AssociatedObject_CollectionChanged
         '   Dim CurrItemsSource As IEnumerable = Me.AssociatedObject.ItemsSource
         '   ItemsSource = TryCast(CurrItemsSource, INotifyCollectionChanged)
         '   AddHandler ItemsSource.CollectionChanged, AddressOf AssociatedObject_CollectionChanged
      End If
   End Sub

   ''' <summary>
   ''' When behavior is detached
   ''' </summary>
   Protected Overrides Sub OnDetaching()
      MyBase.OnDetaching()
      'RemoveHandler Me.AssociatedObject.SelectionChanged, AddressOf AssociatedObject_SelectionChanged
      RemoveHandler ItemsSource.CollectionChanged, AddressOf AssociatedObject_CollectionChanged
   End Sub

End Class

Public Class ScrollIntoViewForDataGrid
   Inherits Behavior(Of DataGrid)

   Private ItemsSource As INotifyCollectionChanged

   Private ListControl As DataGrid

   ''' <summary>
   '''  When Beahvior is attached
   ''' </summary>
   Protected Overrides Sub OnAttached()
      MyBase.OnAttached()
      ListControl = Me.AssociatedObject
      AddHandler Me.AssociatedObject.SelectionChanged, AddressOf AssociatedObject_SelectionChanged
   End Sub


   Private Sub AssociatedObject_CollectionChanged(sender As Object, e As System.Collections.Specialized.NotifyCollectionChangedEventArgs)
      If ListControl.SelectedItem IsNot Nothing Then
         Dim SelectedItemIndex As Integer = ListControl.Items.IndexOf(ListControl.SelectedItem)
         ListControl.Dispatcher.BeginInvoke(DirectCast(Sub()
                                                          ListControl.UpdateLayout()
                                                          If ListControl.SelectedItem IsNot Nothing Then
                                                             ListControl.ScrollIntoView(ListControl.SelectedItem)
                                                          End If
                                                       End Sub, Action))
         If SelectedItemIndex > 0 Then
            ListControl.Dispatcher.BeginInvoke(DirectCast(Sub()
                                                             ListControl.UpdateLayout()
                                                             ListControl.ScrollIntoView(ListControl.Items(SelectedItemIndex - 1))
                                                          End Sub, Action))
         End If
         If SelectedItemIndex < ListControl.Items.Count - 2 Then
            ListControl.Dispatcher.BeginInvoke(DirectCast(Sub()
                                                             ListControl.UpdateLayout()
                                                             ListControl.ScrollIntoView(ListControl.Items(SelectedItemIndex + 1))
                                                          End Sub, Action))
         End If
      End If
   End Sub

   ''' <summary>
   ''' On Selection Changed
   ''' </summary>
   ''' <param name="sender"></param>
   ''' <param name="e"></param>
   Private Sub AssociatedObject_SelectionChanged(sender As Object, e As SelectionChangedEventArgs)
      If IsNothing(ItemsSource) Then
         Dim CurrItemsSource As IEnumerable = Me.AssociatedObject.ItemsSource
         ItemsSource = TryCast(CurrItemsSource, INotifyCollectionChanged)
         AddHandler ItemsSource.CollectionChanged, AddressOf AssociatedObject_CollectionChanged
         RemoveHandler Me.AssociatedObject.SelectionChanged, AddressOf AssociatedObject_SelectionChanged

         ' SE SI CAMBIA ITEMSSOURCE PERDE IL RIFERIMENTO E SMETTE DI FUNZIONARE
         ' PER RIATTIVARLO USARE IL SEGUENTE CODICE COMMENTATO
         'ElseIf ItemsSource IsNot Me.AssociatedObject.ItemsSource Then
         '   Dim PreviousItemsSourceList As INotifyCollectionChanged = TryCast(ItemsSource, INotifyCollectionChanged)
         '   RemoveHandler PreviousItemsSourceList.CollectionChanged, AddressOf AssociatedObject_CollectionChanged
         '   Dim CurrItemsSource As IEnumerable = Me.AssociatedObject.ItemsSource
         '   ItemsSource = TryCast(CurrItemsSource, INotifyCollectionChanged)
         '   AddHandler ItemsSource.CollectionChanged, AddressOf AssociatedObject_CollectionChanged
      End If
   End Sub

   ''' <summary>
   ''' When behavior is detached
   ''' </summary>
   Protected Overrides Sub OnDetaching()
      MyBase.OnDetaching()
      'RemoveHandler Me.AssociatedObject.SelectionChanged, AddressOf AssociatedObject_SelectionChanged
      RemoveHandler ItemsSource.CollectionChanged, AddressOf AssociatedObject_CollectionChanged
   End Sub

End Class