Animated List

animatedlist.dart

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

main() {    
    runApp(new TestSample());
}

class TestSample extends StatelessWidget{
    @override
    Widget build(BuildContext context) {
         var widget = new MaterialApp(
                home: new Scaffold(
                    body: new Center( 
                        child: new AnimatedListDemo(),
                    )
                ),
            );
            return widget;
        }
}

class AnimatedListDemo extends StatefulWidget {
    @override
    _AnimatedListDemoState createState() => new _AnimatedListDemoState();
}

class _AnimatedListDemoState extends State<AnimatedListDemo> with TickerProviderStateMixin {
    int numPresses;
    @override
    void initState() {
        numPresses = 0;
        super.initState();
    }

    Widget build(BuildContext context) {
        return new Center(
            child: new Column(
                mainAxisAlignment: MainAxisAlignment.center,
                crossAxisAlignment: CrossAxisAlignment.center,
                children: [
                    new FlatButton(
                        child: new Text("Press Me - " + numPresses.toString()),
                        onPressed: () {
                            setState(() {
                                numPresses++;               
                            });
                        },
                    ),
                    new Container(
                        child: new AnimatedListSample(),
                        height: 300.0
                    ),
                ]
            )
        );
    }
}

class AnimatedListSample extends StatelessWidget{
    final GlobalKey<AnimatedListState> _listKey =  new GlobalKey<AnimatedListState>();
    ListModel<int> _list;

    AnimatedListSample() {
        _list = new ListModel<int>(
        listKey: _listKey,
        initialItems: <int>[0, 1, 2],
        removedItemBuilder: _buildRemovedItem,
        );
    }

    Widget _buildItem(BuildContext context, int index, Animation<double> animation) {
        TextStyle textStyle = Theme.of(context).textTheme.display1;
        return new Container(
                color: Colors.primaries[index % Colors.primaries.length],
                height: 100.0,
                width: 350.0,
                child: new Center( child:  Text(index.toString(), style: textStyle,) )
                
        );
    }

    Widget _buildRemovedItem(int item, BuildContext context, Animation<double> animation) {
        return _buildItem(context, item, animation);
    }

    @override
    Widget build(BuildContext context) {
        return new AnimatedList(
            scrollDirection: Axis.vertical,
            key: _listKey,
            initialItemCount: _list.length,
            itemBuilder: _buildItem,
        );
    }
}

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