flutter-go/lib/widgets/components/LIst/AnimatedList/model.dart

/**
 * Created with Android Studio.
 * User: 一晟
 * Date: 2018/12/31
 * Time: 下午10:15
 * email: zhu.yan@alibaba-inc.com
 * tartget: FlatButton 的示例
 */
/// Keeps a Dart List in sync with an AnimatedList.
///
/// The [insert] and [removeAt] methods apply to both the internal list and the
/// animated list that belongs to [listKey].
///
/// This class only exposes as much of the Dart List API as is needed by the
/// sample app. More list methods are easily added, however methods that mutate the
/// list must make the same changes to the animated list in terms of
/// [AnimatedListState.insertItem] and [AnimatedList.removeItem].
///
import 'package:flutter/material.dart';

class ListModel<E> {
  ListModel({
    @required this.listKey,
    @required this.removedItemBuilder,
    Iterable<E> initialItems,
  }) : assert(listKey != null),
        assert(removedItemBuilder != null),
        _items =  List<E>.from(initialItems ?? <E>[]);

  final GlobalKey<AnimatedListState> listKey;
  final dynamic removedItemBuilder;
  final List<E> _items;

  AnimatedListState get _animatedList => listKey.currentState;

  void insert(int index, E item) {
    _items.insert(index, item);
    _animatedList.insertItem(index);
  }

  E removeAt(int index) {
    final E removedItem = _items.removeAt(index);
    if (removedItem != null) {
      _animatedList.removeItem(index, (BuildContext context, Animation<double> animation) {
        return removedItemBuilder(removedItem, context, animation);
      });
    }
    return removedItem;
  }

  int get length => _items.length;
  E operator [](int index) => _items[index];
  int indexOf(E item) => _items.indexOf(item);
}