public void urlTextBox_KeyUp(object sender, KeyRoutedEventArgs e)
 {
     if (e.Key == Windows.System.VirtualKey.Enter &&
         !string.IsNullOrWhiteSpace(urlTextBox.Text))
     {
         UrlEntered?.Invoke(this, new RoutedEventArgs());
     }
 }
        public BrowserToolbar()
        {
            this.InitializeComponent();

            urlTextBox.Text = InitialUrl;
            UrlSource       = new System.Uri(InitialUrl);
            UrlEntered?.Invoke(this, new RoutedEventArgs());
        }