How to move focus to previous element from textbox in wpf? - wpf

Question

I have a sample UI and trying to move focus to previous element on pressing Key Up. Can someone help me how to move focus to previous textbox from current Textbox or another elements.
Here is my Sample 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;
}
}