awesome-uiwidgets/AwesomeUIWidgets/Assets/Scripts/Widgets/chat_list.cs

using System;
using System.Collections.Generic;
using uiwidgets;
using Unity.UIWidgets.animation;
using Unity.UIWidgets.async;
using Unity.UIWidgets.foundation;
using Unity.UIWidgets.material;
using Unity.UIWidgets.painting;
using Unity.UIWidgets.ui;
using Unity.UIWidgets.widgets;

namespace UIWidgetsSample
{
    public delegate Widget ItemBuilder(object _object, int? index);

    public class ChatList : StatefulWidget
    {
      /// Used for pagination (infinite scroll) together with [onEndReached].
      /// When true, indicates that there are no more pages to load and
      /// pagination will not be triggered.
      public readonly bool? isLastPage;

        /// Item builder
        public readonly ItemBuilder itemBuilder;

        /// Items to build
        public readonly List<object> items;


        /// Used for pagination (infinite scroll). Called when user scrolls
        /// to the very end of the list (minus [onEndReachedThreshold]).
        public readonly OnEndReached onEndReached;


        /// Used for pagination (infinite scroll) together with [onEndReached].
        /// Can be anything from 0 to 1, where 0 is immediate load of the next page
        /// as soon as scroll starts, and 1 is load of the next page only if scrolled
        /// to the very end of the list. Default value is 0.75, e.g. start loading
        /// next page when scrolled through about 3/4 of the available content.
        public readonly float? onEndReachedThreshold;

        /// Creates a chat list widget
        public ChatList(
            ItemBuilder itemBuilder,
            List<object> items,
            OnEndReached onEndReached = null,
            float? onEndReachedThreshold = null,
            Key key = null,
            bool? isLastPage = null
        ) : base(key)
        {
            this.itemBuilder = itemBuilder;
            this.items = items;
            this.onEndReached = onEndReached;
            this.onEndReachedThreshold = onEndReachedThreshold;
            this.isLastPage = isLastPage;
        }

        public override State createState()
        {
            return new _ChatListState();
        }
    }

    /// [ChatList] widget state
    public  class _ChatListState :  SingleTickerProviderStateMixin<ChatList>
    {
        public AnimationController _controller ;

        public Animation<float> _animation;

        public readonly GlobalKey<SliverAnimatedListState> _listKey = GlobalKey<SliverAnimatedListState>.key();
        public readonly ScrollController _scrollController = new ScrollController();
        private bool _isNextPageLoading;
        public List<object> _oldData ;

        public override void initState()
        {
            base.initState();

            didUpdateWidget(widget);
            _controller = new AnimationController(vsync: this);
            _animation = new CurvedAnimation(
                curve: Curves.easeOutQuad,
                parent: _controller
            );
            _oldData = new List<object>();
            _oldData.AddRange(widget.items);
        }

        public override void didUpdateWidget(StatefulWidget oldWidget)
        {
            oldWidget = (ChatList) oldWidget;
            base.didUpdateWidget(oldWidget);

            _calculateDiffs(((ChatList) oldWidget).items);
        }

        public override void dispose()
        {
            base.dispose();

            _controller.dispose();
            _scrollController.dispose();
        }

        private void _calculateDiffs(List<object> oldList)
        {
            _oldData = new List<object>(widget.items);
            /*var diffResult = calculateListDiff<object>(
                oldList,
                widget.items,
                equalityChecker: (item1, item2) =>
                {
                    if (item1 is Dictionary<string, object> && item2 is Dictionary<string, object>)
                    {
                        var message1 = item1["message"]! as ChatComponents.Message;
                        var message2 = item2["message"]! as ChatComponents.Message;

                        return message1.id == message2.id;
                    }

                    return item1 == item2;
                }
            );
            foreach (var update in diffResult.getUpdates(batch: false))
                update.when(
                    insert: (pos, count) => { _listKey.currentState?.insertItem(pos); },
                    remove: (pos, count) =>
                    {
                        var item = oldList[pos];
                        _listKey.currentState?.removeItem(
                            pos,
                            (_, animation) => _buildRemovedMessage(item, animation)
                        );
                    },
                    change: (pos, payload) => { },
                    move: (from, to) => { }
                );

            _scrollToBottomIfNeeded(oldList);

            _oldData = new List<object>(widget.items);
            
            foreach (var item1 in oldList)
            {
                foreach (var item2 in widget.items)
                {
                    if (item1 is Dictionary<string, object> && item2 is Dictionary<string, object>)
                    {
                        var message1 = ((Dictionary<string, object>)item1)["message"]! as ChatComponents.Message;
                        var message2 =  ((Dictionary<string, object>)item2)["message"]! as ChatComponents.Message;

                        return message1.id == message2.id;
                    }

                    return item1 == item2;
                }
                }
                
            }*/

           
        }

        // Hacky solution to reconsider
        private void _scrollToBottomIfNeeded(List<object> oldList)
        {
            try
            {
                // Take index 1 because there is always a spacer on index 0
                var oldItem = oldList[1];
                var item = widget.items[1];

                // Compare items to fire only on newly added messages
                if (oldItem != item && item is Dictionary<string, object>)
                {
                    var message = ((Dictionary<string, object>) item)["message"] as ChatComponents.Message;

                    // Run only for sent message
                    if (message.author.id ==
                        InheritedUser.of(context).user.id) // Delay to give some time for Flutter to calculate new
                        // size after new message was added
                        Future.delayed(TimeSpan.FromMilliseconds(100), () =>
                        {
                            _scrollController.animateTo(
                                0,
                                TimeSpan.FromMilliseconds(200),
                                Curves.easeInQuad
                            );
                            return default;
                        });
                }
            }
            catch (Exception e)
            {
                // Do nothing if there are no items
            }
        }

        private Widget _buildRemovedMessage(object item, Animation<float> animation)
        {
            return new SizeTransition(
                axisAlignment: -1,
                sizeFactor: animation.drive(new CurveTween(Curves.easeInQuad)),
                child: new FadeTransition(
                    opacity: animation.drive(new CurveTween(Curves.easeInQuad)),
                    child: widget.itemBuilder(item, null)
                )
            );
        }

        private Widget _buildNewMessage(int index, Animation<float> animation)
        {
            try
            {
                var item = _oldData[index];

                return new SizeTransition(
                    axisAlignment: -1,
                    sizeFactor: animation.drive(new CurveTween(Curves.easeOutQuad)),
                    child: widget.itemBuilder(item, index)
                );
            }
            catch (Exception e)
            {
                return new SizedBox();
            }
        }

        public override Widget build(BuildContext context)
        {
            return new NotificationListener<ScrollNotification>(
                onNotification: notification =>
                {
                    if (widget.onEndReached == null || widget.isLastPage == true) return false;

                    if (notification.metrics.pixels >=
                        notification.metrics.maxScrollExtent *
                        (widget.onEndReachedThreshold ?? 0.75))
                    {
                        if (widget.items.isEmpty() || _isNextPageLoading) return false;

                        _controller.duration = new TimeSpan();
                        _controller.forward();

                        setState(() => { _isNextPageLoading = true; });

                        widget.onEndReached().whenComplete(() =>
                        {
                            _controller.duration = TimeSpan.FromMilliseconds(300);
                            _controller.reverse();

                            setState(() => { _isNextPageLoading = false; });
                        });
                    }

                    return false;
                },
                child:
                new CustomScrollView(
                    controller: _scrollController,
                    reverse: true,
                    slivers: new List<Widget>
                    {
                        new SliverPadding(
                            padding: EdgeInsets.only(bottom: 4),
                            sliver: new SliverAnimatedList(
                                initialItemCount: widget.items.Count,
                                key: _listKey,
                                itemBuilder: (_, index, animation) =>
                                    _buildNewMessage(index, animation)
                            )
                        ),
                        new SliverPadding(
                            padding: EdgeInsets.only(
                                top: 16
                            ),
                            sliver: new SliverToBoxAdapter(
                                child: new SizeTransition(
                                    axisAlignment: 1,
                                    sizeFactor: _animation,
                                    child: new Center(
                                        child: new Container(
                                            alignment: Alignment.center,
                                            height: 32,
                                            width: 32,
                                            child: new SizedBox(
                                                height: 16,
                                                width: 16,
                                                child: new CircularProgressIndicator(
                                                    backgroundColor: Colors.transparent,
                                                    strokeWidth: 2,
                                                    valueColor: new AlwaysStoppedAnimation<Color>(
                                                        InheritedChatTheme.of(context).theme.primaryColor
                                                    )
                                                )
                                            )
                                        )
                                    )
                                )
                            )
                        )
                    }
                )
            );
        }
    }
}