16-NotiXamarin - scroll infinito.txt

// BaseNewsListFragment.cs

 protected NewsListAdapter _newsListAdapter;

// INotify.cs

internal interface INotify
    {
        void NotifyObserver();
    }
    
// NewsRepository.cs
    
    internal class NewsRepository
    {
        private List<News> _news;
        private int size = 10;

        public NewsRepository()
        {
            _news = new List<News>();

            for (int i = 1; i <= 30; i++)
            {
                var newNews = new News();

                newNews.Body = "Body " + i.ToString();
                newNews.Title = "Title " + i.ToString();
                newNews.Id = i;
                newNews.ImageName = chooseImage(i);
                _news.Add(newNews);
            }

            string chooseImage(int discriminant)
            {
                switch (discriminant % 3)
                {
                    case 0:
                        return "noticia1.png";
                    case 1:
                        return "noticia2.png";
                    case 2:
                        return "noticia3.png";
                    default:
                        throw new NotImplementedException();
                }
            }
        }

        public List<News> GetNews(int page)
        {
            return _news.Skip((page - 1) * size).Take(size).ToList();
        }

        public News GetNewsById(int Id)
        {
            return _news.FirstOrDefault(x => x.Id == Id);
        }
    }

// newsService.cs

 public List<News> GetNews(int page)
        {
            return _newsRepository.GetNews(page);
        }
    
    // AllNewsListFragment.cs
       internal class AllNewsListFragment : BaseNewsListFragment, INotify
    {
        private NewsService _newsService;
        public int CurrentPage { get; set; }

        public AllNewsListFragment()
        {
            _newsService = new NewsService();
        }

        public override void OnActivityCreated(Bundle savedInstanceState)
        {
            base.OnActivityCreated(savedInstanceState);

            if (!_news.Any())
            {
                CurrentPage = 1;
                _news = _newsService.GetNews(CurrentPage);
            }

            SetupFragment();

            _newsListAdapter.RegisterLoadObserver(this);
        }

        public void NotifyObserver()
        {
            CurrentPage++;
            var nextNews = _newsService.GetNews(CurrentPage);
            if (nextNews.Any())
            {
                _news.AddRange(nextNews);
                _newsListAdapter.AddNews(_news);
                _newsListAdapter.NotifyDataSetChanged();
            }
        }

        public override void OnCreateOptionsMenu(IMenu menu, MenuInflater inflater)
        {
            if (_selectedNews.Count > 0)
            {
                inflater.Inflate(Resource.Menu.newsActionMenu, menu);
            }

            base.OnCreateOptionsMenu(menu, inflater);
        }

        public override bool OnOptionsItemSelected(IMenuItem item)
        {
            switch (item.ItemId)
            {
                case Resource.Id.action_read_later:
                    SaveSelectedNews(_selectedNews);
                    return true;
                default:
                    return base.OnOptionsItemSelected(item);
            }
        }

        private void SaveSelectedNews(List<News> selectedNews)
        {
            try
            {
                var newsLocalService = new NewsLocalService();
                foreach (var news in selectedNews)
                {
                    newsLocalService.Save(news);
                }

                Toast.MakeText(Activity, $"{selectedNews.Count} news saved", ToastLength.Short).Show();
                selectedNews.Clear();
                Activity.InvalidateOptionsMenu();
                UnselectElements();
            }
            catch (Exception ex)
            {
                Toast.MakeText(Activity, ex.Message, ToastLength.Short).Show();
            }
        }
    }
    
// NewsListAdapter

  class NewsListAdapter : BaseAdapter<News>
    {
        private Activity _context;
        private List<News> _news;
        private ISelectedChecker _selectedChecker;
        private INotify _loadObserver;

        public NewsListAdapter(Activity context, List<News> news, ISelectedChecker selectedChecker)
        {
            _context = context;
            _news = news;
            _selectedChecker = selectedChecker;
        }


        public override News this[int position] => _news[position];

        public override int Count => _news.Count;

        public override long GetItemId(int position)
        {
            return this[position].Id;
        }

        public override View GetView(int position, View convertView, ViewGroup parent)
        {
            var item = this[position];

            if (convertView == null)
            {
                convertView = _context.LayoutInflater.Inflate(Resource.Layout.NewsListRow, null);
            }
            else
            {
                var id = (int)GetItemId(position);
                RelativeLayout rl = convertView.FindViewById<RelativeLayout>(Resource.Id.newsListRow_RelativeLayout);

                if (_selectedChecker.IsItemSelected(id))
                {
                    var colorForSelected = _context.Resources.GetString(Resource.Color.listitemselected);
                    rl.SetBackgroundColor(Android.Graphics.Color.ParseColor(colorForSelected));
                }
                else
                {
                    var colorForUnselected = _context.Resources.GetString(Resource.Color.listitemunselected);
                    rl.SetBackgroundColor(Android.Graphics.Color.ParseColor(colorForUnselected));
                }

                if (IsEndOfList(position))
                {
                    NotifyLoadObserver();
                }
            }

            convertView.FindViewById<TextView>(Resource.Id.newsTitle).Text = item.Title;
            var newsImage = convertView.FindViewById<ImageView>(Resource.Id.newsImage);

            var imageURL = string.Concat(ValuesService.ImagesBaseURL, item.ImageName);

            Picasso.With(_context)
                .Load(imageURL)
                .Placeholder(_context.GetDrawable(Resource.Drawable.Icon))
                .Into(newsImage);

            return convertView;
        }

        internal void AddNews(List<News> news)
        {
            _news = news;
        }

        private bool IsEndOfList(int position)
        {
            return position == Count - 1;
        }

        public void RegisterLoadObserver(INotify loadObserver)
        {
            _loadObserver = loadObserver;
        }

        private void NotifyLoadObserver()
        {
            if (_loadObserver != null)
            {
                _loadObserver.NotifyObserver();
            }
        }
    }