Android screenshot

点击一个item选择它,再次点击它会取消选择。点击’+’插入选定的item,点击’ - ‘删除选定的item。 tap处理器会从ListModel<E>中添加或删除items,ListModel<E>List<E>的简单封装 ,用于保持和AnimatedList的同步。 列表模型为其动画列表提供了一个GlobalKey。它使用该键来调用由AnimatedListState定义的insertItem和removeItem方法。

通过flutter create命令创建一个新项目,并用下面的代码替换lib/main.dart的内容来尝试运行一下。

// Copyright 2017 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

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

class AnimatedListSample extends StatefulWidget {
  _AnimatedListSampleState createState() => new _AnimatedListSampleState();

class _AnimatedListSampleState extends State<AnimatedListSample> {
  final GlobalKey<AnimatedListState> _listKey = new GlobalKey<AnimatedListState>();
  ListModel<int> _list;
  int _selectedItem;
  int _nextItem; // The next item inserted when the user presses the '+' button.

  void initState() {
    _list = new ListModel<int>(
      listKey: _listKey,
      initialItems: <int>[0, 1, 2],
      removedItemBuilder: _buildRemovedItem,
    _nextItem = 3;

  // Used to build list items that haven't been removed.
  Widget _buildItem(BuildContext context, int index, Animation<double> animation) {
    return new CardItem(
      animation: animation,
      item: _list[index],
      selected: _selectedItem == _list[index],
      onTap: () {
        setState(() {
          _selectedItem = _selectedItem == _list[index] ? null : _list[index];

  // Used to build an item after it has been removed from the list. This method is
  // needed because a removed item remains  visible until its animation has
  // completed (even though it's gone as far this ListModel is concerned).
  // The widget will be used by the [AnimatedListState.removeItem] method's
  // [AnimatedListRemovedItemBuilder] parameter.
  Widget _buildRemovedItem(int item, BuildContext context, Animation<double> animation) {
    return new CardItem(
      animation: animation,
      item: item,
      selected: false,
      // No gesture detector here: we don't want removed items to be interactive.

  // Insert the "next item" into the list model.
  void _insert() {
    final int index = _selectedItem == null ? _list.length : _list.indexOf(_selectedItem);
    _list.insert(index, _nextItem++);

  // Remove the selected item from the list model.
  void _remove() {
    if (_selectedItem != null) {
      setState(() {
        _selectedItem = null;

  Widget build(BuildContext context) {
    return new MaterialApp(
      home: new Scaffold(
        appBar: new AppBar(
          title: const Text('AnimatedList'),
          actions: <Widget>[
            new IconButton(
              icon: const Icon(Icons.add_circle),
              onPressed: _insert,
              tooltip: 'insert a new item',
            new IconButton(
              icon: const Icon(Icons.remove_circle),
              onPressed: _remove,
              tooltip: 'remove the selected item',
        body: new Padding(
          padding: const EdgeInsets.all(16.0),
          child: new AnimatedList(
            key: _listKey,
            initialItemCount: _list.length,
            itemBuilder: _buildItem,

/// 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].
class ListModel<E> {
    @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);

  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);

/// Displays its integer item as 'item N' on a Card whose color is based on
/// the item's value. The text is displayed in bright green if selected is true.
/// This widget's height is based on the animation parameter, it varies
/// from 0 to 128 as the animation varies from 0.0 to 1.0.
class CardItem extends StatelessWidget {
  const CardItem({
    Key key,
    @required this.animation,
    @required this.item,
    this.selected: false
  }) : assert(animation != null),
       assert(item != null && item >= 0),
       assert(selected != null),
       super(key: key);

  final Animation<double> animation;
  final VoidCallback onTap;
  final int item;
  final bool selected;

  Widget build(BuildContext context) {
    TextStyle textStyle = Theme.of(context).textTheme.display1;
    if (selected)
      textStyle = textStyle.copyWith(color: Colors.lightGreenAccent[400]);
    return new Padding(
      padding: const EdgeInsets.all(2.0),
      child: new SizeTransition(
        axis: Axis.vertical,
        sizeFactor: animation,
        child: new GestureDetector(
          behavior: HitTestBehavior.opaque,
          onTap: onTap,
          child: new SizedBox(
            height: 128.0,
            child: new Card(
              color: Colors.primaries[item % Colors.primaries.length],
              child: new Center(
                child: new Text('Item $item', style: textStyle),

void main() {
  runApp(new AnimatedListSample());