Adding new items to ListBox on Tab keypress

Question

I have a WPF ListBox, with a custom DataTemplate for the ListBox ItemTemplate (each item has a set of controls; i.e. textboxes and datepickers). I have a Behavior attached to the last DatePicker that allows the user to execute ICommand in the event handler for a PreviewKeyDown event.

The idea is that the user will TAB through the controls in the ListBoxItem and when they get to the last control, and press TAB again, a new ListBoxItem get's added to the ListBox. The focus will then move to the first control in the next ListBoxItem. My solution works fine when there are 2 items already in the ListBox, and you're tabbing through the first item. If there's only 1 item in the ListBox, and you get to the last control, the new ListBoxItem is added (as expected) but the focus moves past the ListBox to the next parent control.

It's like the Behavior code gets called and the ICommand gets called, but the TAB event continues on without waiting for the new ListBoxItem to get added.

Any suggestions?

My behavior (ZBehaviorBase is just a class that allows for "better" clean up):

public class TabOffCommandBehavior : ZBehaviorBase<FrameworkElement>
{
    public ICommand TabCommand
    {
        get { return (ICommand)GetValue(CommandProperty); }
        set { SetValue(CommandProperty, value); }
    }

    public static readonly DependencyProperty CommandProperty =
        DependencyProperty.Register("TabCommand", typeof(ICommand), typeof(TabOffCommandBehavior));

    protected override void Initialize()
    {
        this.AssociatedObject.PreviewKeyDown += new KeyEventHandler(AssociatedObject_PreviewKeyDown);
    }

    protected override void Uninitialize()
    {
        if (this.AssociatedObject != null)
        {
            this.AssociatedObject.PreviewKeyDown -= new KeyEventHandler(AssociatedObject_PreviewKeyDown);
        }
    }

    void AssociatedObject_PreviewKeyDown(object sender, KeyEventArgs e)
    {
        // if you want to pass a command param to CanExecute, need to add another dependency property to bind to
        if (TabCommand != null && e.Key == Key.Tab && TabCommand.CanExecute(null))
        {
            TabCommand.Execute(null);
        }
    }

XAML:

<ListBox Grid.Row="1" KeyboardNavigation.TabNavigation="Continue" ItemsSource="{Binding Path=OrderLines, Mode=OneWay}" 
                 ItemTemplate="{DynamicResource LineTemplate}" SelectionMode="Extended">
    <ListBox.ItemContainerStyle>
        <Style TargetType="ListBoxItem">
            <Setter Property="Margin" Value="0,5,0,5"/>                        
            <Setter Property="BorderThickness" Value="1"/>
            <Setter Property="Template" Value="{DynamicResource ListBoxItemTemplate}"/>
            <Setter Property="IsEnabled" Value="{Binding Path=IsLocked, Converter={StaticResource NotBoolConverter}}"/>
            <Setter Property="IsSelected" Value="{Binding Path=IsSelected}"/>
        </Style>
    </ListBox.ItemContainerStyle>
</ListBox>

INSIDE "LineTemplate":

<TextBox Grid.Column="9" Grid.Row="3" Text="{Binding Path=SellPriceOverride, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}" VerticalAlignment="Center" Margin="5,0" TabIndex="10">
    <!--IF ANOTHER INTERACTIVE CONTROL IS ADDED PAST THIS ONE ON THE LINE, THIS COMMENT AND THE BEHAVIOR MUST BE MOVED TO THAT CONTROL INSTEAD-->
    <e:Interaction.Behaviors>
         <ZViewModels:TabOffCommandBehavior TabCommand="{Binding Path=DataContext.AddNewOrderLine, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=ListBox}}"/>
    </e:Interaction.Behaviors>
</TextBox>

The only thing that get's done in the "Execute" method of the command is that an object is added to a collection which is the ItemsSource for the ListBox

Answer 1

Try

if (e.KeyCode == Keys.Tab)

Answer 2

In your AddNewOrderLine method, try setting the focus on the new item that you add. Then to prevent the focus from changing, modify the following code:

void AssociatedObject_PreviewKeyDown(object sender, KeyEventArgs e)
{
    // if you want to pass a command param to CanExecute, need to add another dependency property to bind to
    if (TabCommand != null && e.Key == Key.Tab && TabCommand.CanExecute(null))
    {
        TabCommand.Execute(null);
        e.Handled = true;
    }
}

Answer 3

have you tried this on your ListBox :

<ListBox FocusManager.IsFocusScope="True" ... >

or this:

<ListBox KeyboardNavigation.DirectionalNavigation="Contained" ... >

or both?