Flutter开发之——动画-列表动画AnimatedList

import 'package:flutter/material.dart';
 
void main() => runApp(MyApp());
 
class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: AnimatedListExample(),
    );
  }
}
 
class AnimatedListExample extends StatefulWidget {
  @override
  _AnimatedListExampleState createState() => _AnimatedListExampleState();
}
 
class _AnimatedListExampleState extends State<AnimatedListExample> {
  final GlobalKey<AnimatedListState> _listKey = GlobalKey();
  final List<int> _items = <int>[];
 
  void _addItem() {
    final int index = _items.length;
    _items.add(index);
    _listKey.currentState.insertItem(index);
  }
 
  void _removeItem() {
    if (_items.isNotEmpty) {
      final int index = _items.length - 1;
      _listKey.currentState.removeItem(index, (BuildContext context, Animation<double> animation) {
        return SlideTransition(
          position: Tween<Offset>(
            begin: const Offset(1.0, 0.0),
            end: const Offset(0.0, 0.0),
          ).animate(animation),
          child: Container(
            color: Colors.red,
            child: ListTile(
              title: Text('Item ${_items[index]}'),
            ),
          ),
        );
      });
      _items.removeAt(index);
    }
  }
 
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: AnimatedList(
        key: _listKey,
        initialItemCount: _items.length,
        itemBuilder: (BuildContext context, int index, Animation<double> animation) {
          return SlideTransition(
            position: Tween<Offset>(
              begin: const Offset(1.0, 0.0),
              end: const Offset(0.0, 0.0),
            ).animate(animation),
            child: Container(
              color: Colors.blue,
              child: ListTile(
                title: Text('Item ${_items[index]}'),
              ),
            ),
          );
        },
      ),
      floatingActionButton: Column(
        crossAxisAlignment: CrossAxisAlignment.end,
        mainAxisAlignment: MainAxisAlignment.end,
        children: <Widget>[
          FloatingActionButton(
            onPressed: _addItem,
            tooltip: 'Add',
            child: Icon(Icons.add),
          ),
          SizedBox(height: 8.0),
          FloatingActionButton(
            onPressed: _removeItem,
            tooltip: 'Remove',
            child: