WPF Set Focus on Textbox when Clicking on Button as Behavior

EditNameBehavior.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Interactivity;

namespace myapp.Views
{
    public class EditNameBehavior : Behavior<Button>
    {
        public static readonly DependencyProperty TextBoxProperty =
            DependencyProperty.Register("TextBox", typeof(TextBox), typeof(EditNameBehavior));

        public TextBox TextBox
        {
            get { return (TextBox)GetValue(TextBoxProperty); }
            set { SetValue(TextBoxProperty, value); }
        }

        protected override void OnAttached()
        {
            base.OnAttached();
            this.AssociatedObject.Click += AssociatedObject_Click;
        }

        private void AssociatedObject_Click(object sender, System.Windows.RoutedEventArgs e)
        {
            if (TextBox != null)
            {
                TextBox.SelectAll();
                TextBox.Focus();
            }
        }
    }
}