View a list of Windows phones

I created a Windows Phone 8.1 app with a listing at Startpage.xaml. When I update the list values, I don't see the changes on the phone until I close and open the app again. I tried to refresh the list when I clicked the refresh button, with no success. Does anyone know how to update the list when I click the refresh button?

How I populate the data in the list:

protected async override void OnNavigatedTo(NavigationEventArgs e)
{
    this.navigationHelper.OnNavigatedTo(e);
    HttpClient http = new HttpClient();
    string str = ((ComboBoxItem)cbox.SelectedItem).Content.ToString();
    var response = await http.GetStringAsync("http://mywebpage.si/events/apis/facebook_events.php?city=" + str + "&user=" + uporabnik.user);
    var FSfeed = JsonConvert.DeserializeObject<List<Class1>>(response);

    Reviews.ItemsSource = FSfeed;

}

      

        
        
        
      

    

My class:

public class Class1
{
    public string title { get; set; }
    public string description { get; set; }
    public string image { get; set; }
    public string start { get; set; }
    public string end { get; set; }
    public string location { get; set; }
    public string city { get; set; }
    public int id { get; set; }
}

      

        
        
        
      

    

Refresh button:

    private async void refresh_Click(object sender, RoutedEventArgs e)
    {
    HttpClient http = new HttpClient();
    string str = ((ComboBoxItem)cbox.SelectedItem).Content.ToString();
    var response = await http.GetStringAsync("http://mywebpage.si/events/apis/facebook_events.php?city=" + str + "&user=" + uporabnik.user);
    var FSfeed = JsonConvert.DeserializeObject<List<Class1>>(response);

    Reviews.ItemsSource = FSfeed;
    }

      

        
        
        
      

    

I also tried to update this, but without success:

    private async void refresh_Click(object sender, RoutedEventArgs e)
    {
        this.Frame.Navigate(typeof(PivotPage));
    }