WPF DataGrid ScrollIntoView

Technorati Tags: WPF,DataGrid,ScrollIntoView,bug

In my previous post I talked about using Attached Behaviors to scroll selected item into view. It turns out there is a bug in WPF DataGrid and ScrollIntoView could sometimes throw NullReferenceException when VirtualizingStackPanel.IsVirtualizing="True" .

To avoid this exception there was a solution suggested on this forum http://wpf.codeplex.com/Thread/View.aspx?ThreadId=39458 which basically executes ScrollIntoView on a thread with a very low priority.

Here is my previous solution with suggested work around.

public class DataGridBehavior
{
    #region AutoScrollIntoView

    public static bool GetAutoScrollIntoView(DataGrid dataGrid)
    {
        return (bool)dataGrid.GetValue(AutoScrollIntoViewProperty);
    }

    public static void SetAutoScrollIntoView(
      DataGrid dataGrid, bool value)
    {
        dataGrid.SetValue(AutoScrollIntoViewProperty, value);
    }

    public static readonly DependencyProperty AutoScrollIntoViewProperty =
        DependencyProperty.RegisterAttached(
        "AutoScrollIntoView",
        typeof(bool),
        typeof(DataGridBehavior),
        new UIPropertyMetadata(false, OnAutoScrollIntoViewWhenSelectionChanged));

    static void OnAutoScrollIntoViewWhenSelectionChanged(
      DependencyObject depObj, DependencyPropertyChangedEventArgs e)
    {
        DataGrid dataGrid = depObj as DataGrid;
        if (dataGrid == null)
            return;

        if (!(e.NewValue is bool))
            return;

        if ((bool)e.NewValue)
            dataGrid.SelectionChanged += OnDataGridSelectionChanged;
        else
            dataGrid.SelectionChanged -= OnDataGridSelectionChanged;
    }

    static void OnDataGridSelectionChanged(object sender, RoutedEventArgs e)
    {
        // Only react to the SelectionChanged event raised by the DataGrid
        // Ignore all ancestors.
        if (!Object.ReferenceEquals(sender, e.OriginalSource))
            return;

        DataGrid dataGrid = e.OriginalSource as DataGrid;
        if (dataGrid != null && dataGrid.SelectedItem != null)
        {
            // this is a workaround to fix the layout issue.
            // otherwise ScrollIntoView should work directly. 
            dataGrid.Dispatcher.BeginInvoke(DispatcherPriority.Loaded, new DispatcherOperationCallback(ScrollItemIntoView),dataGrid); 
        }
    }

    static object ScrollItemIntoView(object sender)
    {
        DataGrid dataGrid = sender as DataGrid;
        if (dataGrid != null && dataGrid.SelectedItem != null)
        {
            dataGrid.ScrollIntoView(dataGrid.SelectedItem);
        }
        return null; 
    }

    #endregion // AutoScrollIntoView

Happy Coding!