WPF DataGrid не возвращает DataGridRow

Я использую DataGrid в приложении WPF, используя цикл for для извлечения DataGridRow один за другим до последнего, в настоящее время я сортирую datagrid с помощью ICollectionView после использования ICollectionView, мой цикл for не работает.

Код XAML:

<DataGrid VerticalAlignment="Stretch" HorizontalAlignment="Stretch" x:Name="GridTest"  ItemsSource="{Binding}" AutoGenerateColumns="False" CanUserSortColumns="False" CanUserResizeRows="False" AreRowDetailsFrozen="True" CanUserResizeColumns="False" CanUserDeleteRows="False" IsReadOnly="True">
                <DataGrid.Columns>
                    <DataGridTextColumn  Header="SNo" Width="0.25*" Binding="{Binding Path=SNo}" CanUserResize="False" />
                    <DataGridTextColumn Header="SalaryAmt" Width="0.25*" Binding="{Binding Path=SalaryAmt}" CanUserResize="False" />
                    <DataGridTextColumn Header="Name" Width="0.20*" Binding="{Binding Path=Name}" CanUserResize="False"/>
                    <DataGridTextColumn Header="Address" Width="0.30*" Binding="{Binding Path=Address}" CanUserResize="False"/>
                </DataGrid.Columns>
</DataGrid>

код позади:

namespace SortGrid
{
    public partial class TestDG
    {
    Dictionary<string, GridStructure> Dict1;
    ObservableCollection<GridStructure> List1 = new ObservableCollection<GridStructure>();
    private ICollectionView _currentView;
    _currentView = CollectionViewSource.GetDefaultView(List1);
    _currentView.SortDescriptions.Add(new SortDescription("SalaryAmt", ListSortDirection.Ascending));
    void DispatchTime_Tick(object sender, EventArgs e)
    {
    Dict1.Clear();
    _currentView.Refresh();
    GridColors(GridTest_TierColors, GridTest);
    }
    private void GridColors(Brush[] col, DataGrid Grid)
    {
    int colorind = 0;
    for (int rowind = 0; rowind < Grid.Items.Count; rowind++)
    {
    DataGridRow row = (DataGridRow)Grid.ItemContainerGenerator.ContainerFromIndex(rowind);
    if (row != null)
    {
    //conditional formatting here
    }
    }
    }
    }
}