Imports System.Collections.ObjectModel
Imports System.Collections.Specialized

Public Class EgtDataGrid

   Sub New()
      InitializeComponent()
   End Sub

   Public Shadows Property BindingColumns As ObservableCollection(Of String)
      Get
         Return CType(MyBase.GetValue(BindingColumnsProperty), ObservableCollection(Of String))
      End Get
      Set(value As ObservableCollection(Of String))
         MyBase.SetValue(BindingColumnsProperty, value)
      End Set
   End Property

   Public Shared ReadOnly BindingColumnsProperty As DependencyProperty = DependencyProperty.Register("BindingColumns", GetType(ObservableCollection(Of String)), GetType(EgtDataGrid), New FrameworkPropertyMetadata(New ObservableCollection(Of String), New PropertyChangedCallback(AddressOf OnDataGridColumnsPropertyChanged)) With {.BindsTwoWayByDefault = True})

   Private Shared Sub OnDataGridColumnsPropertyChanged(ByVal source As DependencyObject, ByVal e As DependencyPropertyChangedEventArgs)
      Dim context = TryCast(source, EgtDataGrid)
      Dim oldItems = TryCast(e.OldValue, ObservableCollection(Of String))

      If oldItems IsNot Nothing Then

         For Index = 0 To oldItems.Count - 1
            Dim Column As DataGridColumn = context.FindResource(oldItems(Index))
            context.Columns.Remove(Column)
         Next

         RemoveHandler oldItems.CollectionChanged, AddressOf context.collectionChanged
      End If

      Dim newItems = TryCast(e.NewValue, ObservableCollection(Of String))

      If newItems IsNot Nothing Then

         For Index = 0 To newItems.Count - 1
            Dim col As DataGridColumn = context.FindResource(newItems(Index))
            context.Columns.Add(col)
         Next

         AddHandler newItems.CollectionChanged, AddressOf context.collectionChanged
      End If
   End Sub

   Private Sub collectionChanged(ByVal sender As Object, ByVal e As NotifyCollectionChangedEventArgs)
      Select Case e.Action
         Case NotifyCollectionChangedAction.Add

            If e.NewItems IsNot Nothing Then

               For Each one As String In e.NewItems
                  Dim col As DataGridColumn = CurrDataGrid.FindResource(one)
                  CurrDataGrid.Columns.Insert(e.NewStartingIndex, col)
                  If col.DisplayIndex <> e.NewStartingIndex Then
                     CurrDataGrid.Columns(e.NewStartingIndex).DisplayIndex = e.NewStartingIndex
                  End If
               Next
            End If

         Case NotifyCollectionChangedAction.Remove

            If e.OldItems IsNot Nothing Then

               For Each one As String In e.OldItems
                  Dim col As DataGridColumn = CurrDataGrid.FindResource(one)
                  CurrDataGrid.Columns.Remove(col)
               Next
            End If

         Case NotifyCollectionChangedAction.Move
            'Dim col As DataGridColumn = CurrDataGrid.FindResource(BindingColumns(e.OldStartingIndex))
            'col.DisplayIndex = e.NewStartingIndex
            CurrDataGrid.Columns.Move(e.OldStartingIndex, e.NewStartingIndex)
            CurrDataGrid.Columns(e.NewStartingIndex).DisplayIndex = e.NewStartingIndex
            'Dim x = CurrDataGrid.Columns(e.OldStartingIndex).DisplayIndex
         Case NotifyCollectionChangedAction.Reset
            CurrDataGrid.Columns.Clear()

            If e.NewItems IsNot Nothing Then

               For Each one As DataGridColumn In e.NewItems
                  Dim col As DataGridColumn = CurrDataGrid.FindResource(one)
                  CurrDataGrid.Columns.Add(col)
               Next
            End If
         Case NotifyCollectionChangedAction.Replace
            Dim col As DataGridColumn = CurrDataGrid.FindResource(e.NewItems(0))
            CurrDataGrid.Columns(e.NewStartingIndex) = col
      End Select
   End Sub
End Class