Animated Stream List In Flutter

animated_stream_list.dart

export 'package:fluttertutorial/animated_list/animated_stream_list.dart';

home_page.dart

home_page.dart

Main.dart

import 'package:flutter/material.dart';

import 'home_page.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Animated Stream List',
      home: HomePage(),
    );
  }
}

todo.dart

class Todo implements Comparable<Todo> {
  final String title;
  final String content;
  DateTime _changedAt;
  bool _done;

  Todo({this.title, this.content})
      : _changedAt = DateTime.now(),
        _done = false;

  DateTime get changedAt => _changedAt;
  bool get done => _done;

  set done(bool done) {
    _done = done;
    _changedAt = DateTime.now();
  }

  @override
  bool operator ==(other) => other is Todo && other._changedAt == _changedAt;

  @override
  int get hashCode => _changedAt.hashCode;

  @override
  int compareTo(Todo other) =>
      this._changedAt.millisecondsSinceEpoch -
      other._changedAt.millisecondsSinceEpoch;
}

todos_bloc.dart

import 'dart:async';
import 'todo.dart';

class TodoBloc {
  final List<Todo> _todoList = [];

  final StreamController<List<Todo>> _todoListStream = StreamController();
  Stream<List<Todo>> get todoListStream => _todoListStream.stream;

  TodoBloc() {
    _todoListStream.add(_todoList);
  }

  void addTodo(Todo todo) {
    _todoList.add(todo);
    _todoList.sort();
    _todoListStream.add(_todoList);
  }

  void removeTodo(int index) {
    _todoList.removeAt(index);
    _todoListStream.add(_todoList);
  }

  void toggleDone(int index) {
    final todo = _todoList[index];
    todo.done = !todo.done;
    _todoListStream.add(_todoList);
  }

  void dispose() {
    _todoListStream.close();
  }
}

animated_stream_list.dart

import 'dart:async';

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';

import 'package:fluttertutorial/animated_list/diff_applier.dart';
import 'package:fluttertutorial/animated_list/list_controller.dart';
import 'package:fluttertutorial/animated_list/myers_diff.dart';

class AnimatedStreamList<E> extends StatefulWidget {
  final Stream<List<E>> streamList;
  final List<E> initialList;
  final AnimatedStreamListItemBuilder<E> itemBuilder;
  final AnimatedStreamListItemBuilder<E> itemRemovedBuilder;
  final Axis scrollDirection;
  final bool reverse;
  final ScrollController scrollController;
  final bool primary;
  final ScrollPhysics scrollPhysics;
  final bool shrinkWrap;
  final EdgeInsetsGeometry padding;
  final Equalizer equals;

  AnimatedStreamList({
    @required this.streamList,
    this.initialList,
    @required this.itemBuilder,
    @required this.itemRemovedBuilder,
    this.scrollDirection: Axis.vertical,
    this.reverse: false,
    this.scrollController,
    this.primary,
    this.scrollPhysics,
    this.shrinkWrap: false,
    this.padding,
    this.equals,
  });

  @override
  State<StatefulWidget> createState() => _AnimatedStreamListState<E>();
}

class _AnimatedStreamListState<E> extends State<AnimatedStreamList<E>> with WidgetsBindingObserver {
  final GlobalKey<AnimatedListState> _globalKey = GlobalKey();
  ListController<E> _listController;
  DiffApplier<E> _diffApplier;
  DiffUtil<E> _diffUtil;
  StreamSubscription<List<E>> _subscription;

  void startListening() {
    _subscription?.cancel();
    _subscription = widget.streamList.listen((list) async {
      final diffList = await _diffUtil.calculateDiff(_listController.items, list, equalizer: widget.equals);
      _diffApplier.applyDiffs(diffList);
    });
  }

  void stopListening() {
    _subscription?.cancel();
    _subscription = null;
  }

  @override
  void initState() {
    super.initState();
    _listController = ListController(
      key: _globalKey,
      items: widget.initialList ?? <E>[],
      itemRemovedBuilder: widget.itemRemovedBuilder,
    );

    _diffApplier = DiffApplier(_listController);
    _diffUtil = DiffUtil();

    startListening();
  }

  @override
  void dispose() {
    stopListening();
    super.dispose();
  }

  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    switch (state) {
      case AppLifecycleState.resumed:
        startListening();
        break;
      case AppLifecycleState.paused:
        stopListening();
        break;
      default:
        break;
    }
  }

  @override
  Widget build(BuildContext context) {
    return AnimatedList(
      initialItemCount: _listController.items.length,
      key: _globalKey,
      scrollDirection: widget.scrollDirection,
      reverse: widget.reverse,
      primary: widget.primary,
      controller: widget.scrollController,
      physics: widget.scrollPhysics,
      padding: widget.padding,
      shrinkWrap: widget.shrinkWrap,
      itemBuilder:
          (BuildContext context, int index, Animation<double> animation) =>
              widget.itemBuilder(
                _listController[index],
                index,
                context,
                animation,
              ),
    );
  }
}

diff_applier.dart

import 'package:fluttertutorial/animated_list/diff_payload.dart';
import 'package:fluttertutorial/animated_list/list_controller.dart';

class DiffApplier<E> {
  final ListController<E> _controller;
  final DiffVisitor _visitor;

  DiffApplier(this._controller) : _visitor = _Visitor(_controller);

  void applyDiffs(List<Diff> diffs) {
    diffs.forEach((diff) => diff.accept(_visitor));
  }
}

class _Visitor<E> implements DiffVisitor {
  final ListController<E> _controller;

  const _Visitor(this._controller);

  @override
  void visitChangeDiff(ChangeDiff diff) {
    if (diff.size > diff.items.length) {
      int sizeDifference = diff.size - diff.items.length;
      while (sizeDifference > 0) {
        _controller.removeItemAt(diff.index + sizeDifference);
        sizeDifference--;
      }
    } else if (diff.items.length > diff.size) {
      int insertIndex = diff.size;
      while (insertIndex < diff.items.length) {
        _controller.insert(insertIndex + diff.index, diff.items[insertIndex]);
        insertIndex++;
      }
    }

    final changedItems = diff.items.take(diff.size).toList();
    _controller.listChanged(diff.index, changedItems);
  }

  @override
  void visitDeleteDiff(DeleteDiff diff) {
    for (int i = 0; i < diff.size; i++) {
      _controller.removeItemAt(diff.index);
    }
  }

  @override
  void visitInsertDiff(InsertDiff diff) {
    for (int i = 0; i < diff.size; i++) {
      _controller.insert(diff.index + i, diff.items[i]);
    }
  }
}

diff_payload.dart

abstract class DiffVisitor {
  void visitInsertDiff(InsertDiff diff);

  void visitDeleteDiff(DeleteDiff diff);

  void visitChangeDiff(ChangeDiff diff);
}

abstract class Diff implements Comparable<Diff> {
  final int index;
  final int size;

  const Diff(this.index, this.size);

  @override
  String toString() {
    return "${this.runtimeType.toString()} index: $index, size: $size";
  }

  @override
  int compareTo(Diff other) => index - other.index;

  void accept(DiffVisitor visitor);
}

class InsertDiff<E> extends Diff {
  final List<E> items;

  InsertDiff(int index, int size, this.items) : super(index, size);

  @override
  void accept(DiffVisitor visitor) => visitor.visitInsertDiff(this);
}

class DeleteDiff extends Diff {
  DeleteDiff(int index, int size) : super(index, size);

  @override
  void accept(DiffVisitor visitor) => visitor.visitDeleteDiff(this);
}

class ChangeDiff<E> extends Diff {
  final List<E> items;

  ChangeDiff(int index, int size, this.items) : super(index, size);

  @override
  void accept(DiffVisitor visitor) => visitor.visitChangeDiff(this);
}

list_controller.dart

import 'package:flutter/material.dart';

typedef Widget AnimatedStreamListItemBuilder<T>(
  T item,
  int index,
  BuildContext context,
  Animation<double> animation,
);

class ListController<E> {
  final GlobalKey<AnimatedListState> key;
  final List<E> items;
  final Duration duration;
  final AnimatedStreamListItemBuilder<E> itemRemovedBuilder;

  ListController({
    @required this.key,
    @required this.items,
    @required this.itemRemovedBuilder,
    this.duration = const Duration(milliseconds: 300),
  })  : assert(key != null),
        assert(itemRemovedBuilder != null),
        assert(items != null);

  AnimatedListState get _list => key.currentState;

  void insert(int index, E item) {
    items.insert(index, item);

    _list.insertItem(index, duration: duration);
  }

  void removeItemAt(int index) {
    E item = items.removeAt(index);
    _list.removeItem(
      index,
      (BuildContext context, Animation<double> animation) =>
          itemRemovedBuilder(item, index, context, animation),
      duration: duration,
    );
  }

  void listChanged(int startIndex, List<E> itemsChanged) {
    int i = 0;
    for (E item in itemsChanged) {
      items[startIndex + i] = item;
      i++;
    }

    // ignore: invalid_use_of_protected_member
    _list.setState(() {});
  }

  int get length => items.length;

  E operator [](int index) => items[index];

  int indexOf(E item) => items.indexOf(item);
}

myers_diff.dart

import 'package:flutter/foundation.dart';
import 'package:fluttertutorial/animated_list/diff_payload.dart';
import 'package:fluttertutorial/animated_list/path_node.dart';

typedef bool Equalizer(dynamic item1, dynamic item2);

class DiffUtil<E> {
  static Equalizer eq;

  Future<List<Diff>> calculateDiff(List<E> oldList, List<E> newList,
      {Equalizer equalizer}) {
    eq = equalizer;
    final args = _DiffArguments<E>(oldList, newList);
    return compute(_myersDiff, args);
  }
}

class _DiffArguments<E> {
  final List<E> oldList;
  final List<E> newList;

  _DiffArguments(this.oldList, this.newList);
}

List<Diff> _myersDiff<E>(_DiffArguments<E> args) {
  final List<E> oldList = args.oldList;
  final List<E> newList = args.newList;

  if (oldList == null) throw ArgumentError("oldList is null");
  if (newList == null) throw ArgumentError("newList is null");

  if (oldList == newList) return [];

  final oldSize = oldList.length;
  final newSize = newList.length;

  if (oldSize == 0) {
    return [InsertDiff(0, newSize, newList)];
  }

  if (newSize == 0) {
    return [DeleteDiff(0, oldSize)];
  }

  final equals = DiffUtil.eq != null ? DiffUtil.eq : (a, b) => a == b;
  final path = _buildPath(oldList, newList, equals);
  final diffs = _buildPatch(path, oldList, newList)..sort();
  return diffs.reversed.toList(growable: true);
}

PathNode _buildPath<E>(List<E> oldList, List<E> newList, Equalizer equals) {
  final oldSize = oldList.length;
  final newSize = newList.length;

  final int max = oldSize + newSize + 1;
  final size = (2 * max) + 1;
  final int middle = size ~/ 2;
  final List<PathNode> diagonal = List(size);

  diagonal[middle + 1] = Snake(0, -1, null);
  for (int d = 0; d < max; d++) {
    for (int k = -d; k <= d; k += 2) {
      final int kmiddle = middle + k;
      final int kplus = kmiddle + 1;
      final int kminus = kmiddle - 1;
      PathNode prev;

      int i;
      if ((k == -d) ||
          (k != d &&
              diagonal[kminus].originIndex < diagonal[kplus].originIndex)) {
        i = diagonal[kplus].originIndex;
        prev = diagonal[kplus];
      } else {
        i = diagonal[kminus].originIndex + 1;
        prev = diagonal[kminus];
      }

      diagonal[kminus] = null;

      int j = i - k;

      PathNode node = DiffNode(i, j, prev);

      while (i < oldSize && j < newSize && equals(oldList[i], newList[j])) {
        i++;
        j++;
      }
      if (i > node.originIndex) {
        node = Snake(i, j, node);
      }

      diagonal[kmiddle] = node;

      if (i >= oldSize && j >= newSize) {
        return diagonal[kmiddle];
      }
    }
    diagonal[middle + d - 1] = null;
  }

  throw Exception();
}

List<Diff> _buildPatch<E>(PathNode path, List<E> oldList, List<E> newList) {
  if (path == null) throw ArgumentError("path is null");

  final List<Diff> diffs = List();
  if (path.isSnake()) {
    path = path.previousNode;
  }
  while (path != null &&
      path.previousNode != null &&
      path.previousNode.revisedIndex >= 0) {
    if (path.isSnake()) throw Exception();
    int i = path.originIndex;
    int j = path.revisedIndex;

    path = path.previousNode;
    int iAnchor = path.originIndex;
    int jAnchor = path.revisedIndex;

    List<E> original = oldList.sublist(iAnchor, i);
    List<E> revised = newList.sublist(jAnchor, j);

    if (original.length == 0 && revised.length != 0) {
      diffs.add(InsertDiff(iAnchor, revised.length, revised));
    } else if (original.length > 0 && revised.length == 0) {
      diffs.add(DeleteDiff(iAnchor, original.length));
    } else {
      diffs.add(ChangeDiff(iAnchor, original.length, revised));
    }

    if (path.isSnake()) {
      path = path.previousNode;
    }
  }

  return diffs;
}

path_node.dart

abstract class PathNode {
  final int originIndex;
  final int revisedIndex;
  final PathNode previousNode;

  PathNode(this.originIndex, this.revisedIndex, this.previousNode);

  bool isSnake();

  bool isBootStrap() => originIndex < 0 || revisedIndex < 0;

  PathNode previousSnake() {
    if (isBootStrap()) return null;
    if (!isSnake() && previousNode != null) return previousNode.previousSnake();
    return this;
  }

  @override
  String toString() {
    final buffer = StringBuffer();
    buffer.write("[");
    PathNode node = this;
    while (node != null) {
      buffer.write("(");
      buffer.write("${node.originIndex.toString()}");
      buffer.write(",");
      buffer.write("${node.revisedIndex.toString()}");
      buffer.write(")");
      node = node.previousNode;
    }
    buffer.write("]");
    return buffer.toString();
  }
}

class Snake extends PathNode {
  Snake(int originIndex, int revisedIndex, PathNode previousNode)
      : super(originIndex, revisedIndex, previousNode);

  @override
  bool isSnake() => true;
}

class DiffNode extends PathNode {
  DiffNode(int originIndex, int revisedIndex, PathNode previousNode)
      : super(originIndex, revisedIndex,
            previousNode == null ? null : previousNode.previousSnake());

  @override
  bool isSnake() => false;
}

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