问有没有办法知道在WPF应用程序中哪一项是焦点？

EN

FocusManager.GetFocusedElement(this); // where this is Window1

<Window x:Class="StackOverflowTests.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" KeyDown="window1_KeyDown"
    Title="Window1" x:Name="window1" Height="300" Width="300">
    <StackPanel>
        <TextBox x:Name="textBox1" />
        <TextBox x:Name="textBox2" />
        <TextBox x:Name="textBox3" />
        <TextBox x:Name="textBox4" />
        <TextBox x:Name="textBox5" />
    </StackPanel>
</Window>

using System.Windows;
using System.Windows.Input;

namespace StackOverflowTests
{
    /// <summary>
    /// Interaction logic for Window1.xaml
    /// </summary>
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();
        }

        private void window1_KeyDown(object sender, System.Windows.Input.KeyEventArgs e)
        {
            if(e.Key == Key.Return)
                MessageBox.Show((FocusManager.GetFocusedElement(this) as FrameworkElement).Name);
        }
    }
}