Gallery/Gallery.Share/Views/GalleryPage.xaml.cs

using System.Collections.Generic;
using System.Threading.Tasks;
using Gallery.Resources;
using Gallery.Resources.UI;
using Gallery.Util;
using Gallery.Util.Interface;
using Gallery.Util.Model;
using Xamarin.Essentials;
using Xamarin.Forms;

namespace Gallery.Views
{
    public partial class GalleryPage : GalleryCollectionPage
    {
        public static readonly BindableProperty ToolbarCommandProperty = BindableProperty.Create(nameof(ToolbarCommand), typeof(Command), typeof(GalleryPage));
        public Command ToolbarCommand
        {
            get => (Command)GetValue(ToolbarCommandProperty);
        }

        private int currentPage;

        public GalleryPage(IGallerySource source) : base(source)
        {
            Title = Helper.GetResource(source.Name);
            Resources.Add("cardView", GetCardViewTemplate());
            SetValue(ToolbarCommandProperty, new Command(DoRefresh, () => !IsLoading && !IsBottomLoading));
            InitializeComponent();

            currentPage = 1;
        }

        protected override ActivityIndicator LoadingIndicator => activityLoading;

        protected override void OnAppearing()
        {
            if (currentPage != 1 && Gallery == null)
            {
                currentPage = 1;
            }
            if (Store.FavoriteList.Changed && Source is Sources.FavoriteGallerySource)
            {
                Store.FavoriteList.Reload();
                LastUpdated = default;
            }
            base.OnAppearing();
        }

        protected override void BeforeLoading()
        {
            MainThread.BeginInvokeOnMainThread(ToolbarCommand.ChangeCanExecute);
        }

        protected override void AfterLoaded()
        {
            MainThread.BeginInvokeOnMainThread(ToolbarCommand.ChangeCanExecute);
        }

        protected override async Task<IEnumerable<GalleryItem>> DoloadGalleryData(bool force)
        {
            var result = await Source.GetRecentItemsAsync(currentPage);
            return result;
        }

        protected override IEnumerable<GalleryItem> DoGetGalleryList(IEnumerable<GalleryItem> data, out int tag)
        {
            tag = currentPage;
            return data;
        }

        protected override void OnGalleryItemTapped(GalleryItem item)
        {
            if (item == null)
            {
                return;
            }
            Start(async () =>
            {
                var page = new GalleryItemPage(item);
                await Navigation.PushAsync(page);
            });
        }

        private void DoRefresh()
        {
            if (IsLoading)
            {
                return;
            }
            Start(async () =>
            {
                await ScrollToTopAsync(scrollView);
                StartLoading(force: true);
            });
        }

        private void FlowLayout_MaxHeightChanged(object sender, HeightEventArgs e)
        {
            SetOffset(e.ContentHeight - scrollView.Bounds.Height - SCROLL_OFFSET);
        }

        protected override bool CheckRefresh()
        {
            if (!Source.IsScrollable)
            {
                return false;
            }
            currentPage++;
#if DEBUG
            Log.Print($"loading page: {currentPage}");
#endif
            return true;
        }

        private void ScrollView_Scrolled(object sender, ScrolledEventArgs e)
        {
            var y = e.ScrollY;
            OnScrolled(y);
        }
    }
}