WPF DataGrid moves input focus and selection to the wrong cell when pressing tab

You’d expect that when you hit tab in the last cell the WPF data grid it would create a new row and put your focus in the first cell of that row.  It doesn’t, depending on how you have KeboardNavigation.TabNavigation set it’ll jump off somewhere you don’t expect, like the next control or back to the first item in the grid.

I was sure I was doing something wrong because it can’t behave like this, it’s just plain unusable.  But after some time I found this which suggests it’s a bug.  So, given that it didn’t look I was missing something obvious I wrote this behavior to solve the problem:

public class NewLineOnTabBehavior : Behavior<DataGrid>

{

    private bool _monitorForTab;

    protected override void OnAttached()

    {

        base.OnAttached();

        AssociatedObject.BeginningEdit += _EditStarting;

        AssociatedObject.CellEditEnding += _CellEnitEnding;

        AssociatedObject.PreviewKeyDown += _KeyDown;

    }

    private void _EditStarting(object sender, DataGridBeginningEditEventArgs e)

    {

        if (e.Column.DisplayIndex == AssociatedObject.Columns.Count - 1)

            _monitorForTab = true;

    }

    private void _CellEnitEnding(object sender, DataGridCellEditEndingEventArgs e)

    {

        _monitorForTab = false;

    }

    private void _KeyDown(object sender, KeyEventArgs e)

    {

        if (_monitorForTab && e.Key == Key.Tab)

        {

            AssociatedObject.CommitEdit(DataGridEditingUnit.Row, false);

        }

    }

    protected override void OnDetaching()

    {

        base.OnDetaching();

        AssociatedObject.BeginningEdit -= _EditStarting;

        AssociatedObject.CellEditEnding -= _CellEnitEnding;

        AssociatedObject.PreviewKeyDown -= _KeyDown;

        _monitorForTab = false;

    }

}

 

You use it like this:

<DataGrid ItemsSource="{Binding Stuff}" CanUserAddRows="True" CanUserDeleteRows="True" 

    AutoGenerateColumns="false" KeyboardNavigation.TabNavigation="Contained">

    <i:Interaction.Behaviors>

        <Infrastructure:NewLineOnTabBehavior />

    </i:Interaction.Behaviors>

    <DataGrid.Columns>

        <DataGridTextColumn Binding="{Binding Something}" />

        <DataGridTextColumn Binding="{Binding SomethingDifferent}" />

    </DataGrid.Columns>

</DataGrid>

 

I found that setting the KeyboardNavigation.TabNavigation to Contained behaved quite nicely.

If anyone has a better approach please let me know.  If not, I hope this saves you some time!