如何将焦点从WPF中的文本框移至以前的元素？

Question

我有一个示例UI，并试图将重点转移到以前的元素上，以按下键。有人可以帮助我如何将焦点从当前文本框或其他元素移至以前的文本框。

这是我的样本UI

        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:Sample_Application"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">

    <DockPanel PreviewKeyDown="DockPanel_PreviewKeyDown" PreviewKeyUp="DockPanel_PreviewKeyUp" KeyUp="DockPanel_KeyUp" >
        <TextBox DockPanel.Dock="Top" Margin="18,0,0,0" HorizontalAlignment="Left" TextWrapping="Wrap" Text="TextBox" VerticalAlignment="Top" Width="120"/>
        <TextBox DockPanel.Dock="Top" Margin="18,8,0,0" HorizontalAlignment="Left"  TextWrapping="Wrap" Text="TextBox" VerticalAlignment="Top" Width="120"/>
        <CheckBox DockPanel.Dock="Top" Margin="18,8,0,0" Content="CheckBox" HorizontalAlignment="Left"  VerticalAlignment="Top"/>
        <CheckBox DockPanel.Dock="Top" Margin="18,8,0,0"  Content="CheckBox" HorizontalAlignment="Left"  VerticalAlignment="Top"/>
        <RadioButton DockPanel.Dock="Top" Margin="18,8,0,0"  Content="RadioButton" HorizontalAlignment="Left"  VerticalAlignment="Top"/>
        <RadioButton DockPanel.Dock="Top" Margin="18,8,0,0"  Content="RadioButton" HorizontalAlignment="Left"  VerticalAlignment="Top"/>
        <StackPanel>
            <TextBox HorizontalAlignment="Left" Margin="153,34,0,0"  TextWrapping="Wrap" Text="TextBox" VerticalAlignment="Top" Width="120"/>
            <TextBox HorizontalAlignment="Left" Margin="153,10,0,0" TextWrapping="Wrap" Text="TextBox" VerticalAlignment="Top" Width="120"/>
            <CheckBox Content="CheckBox" HorizontalAlignment="Left" Margin="153,10,0,0" VerticalAlignment="Top"/>
        </StackPanel>
    </DockPanel>
</Window>

Below is my code behind

        private void DockPanel_PreviewKeyUp(object sender, KeyEventArgs e)
        {
            if (e.Key == Key.Up && e.OriginalSource is TextBox)
            {
                FocusNavigationDirection focusDirection = FocusNavigationDirection.Previous;
                TraversalRequest request = new TraversalRequest(focusDirection);
                UIElement elementWithFocus = Keyboard.FocusedElement as UIElement;

                // Change keyboard focus.
                if (elementWithFocus != null)
                {
                    if (elementWithFocus.MoveFocus(request)) e.Handled = true;
                }
                e.Handled = true;
            }
        }