async void OnListViewItemTapped(object sender, ItemTappedEventArgs e)
        {
            ChatPreview tappedItem = e.Item as ChatPreview;
            var         detail     = new BeaconClient.ChatInterface();

            detail.fromPreview = tappedItem;
            await Navigation.PushAsync(detail);
        }
 void OnListViewItemSelected(object sender, SelectedItemChangedEventArgs e)
 {
     ChatPreview selectedItem = e.SelectedItem as ChatPreview;
 }