animated_list.dart

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Material App',
      home: Home(),
    );
  }
}

class Home extends StatefulWidget {
  const Home({
    Key? key,
  }) : super(key: key);

  @override
  _HomeState createState() => _HomeState();
}

class _HomeState extends State<Home> {
  final list = <String>[];
  @override
  void initState() {
    super.initState();
    list.addAll(
        List.generate(10, (index) => 'Item ${index + 1}', growable: true));
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Material App Bar')),
      body: _List(
        list: list,
        onDelete: (index) => setState(() => list.removeAt(index)),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          setState(() {
            list.add('Item ${list.length + 1}');
          });
        },
        child: Icon(Icons.add),
      ),
    );
  }
}

class _List extends StatefulWidget {
  _List({
    Key? key,
    required this.list,
    required this.onDelete,
  }) : super(key: key);
  final List<String> list;
  final ValueChanged<int> onDelete;
  @override
  __ListState createState() => __ListState();
}

class __ListState extends State<_List> with TickerProviderStateMixin {
  final animationControllers = <AnimationController>[];
  @override
  void initState() {
    super.initState();
    initControllers(widget.list.length);
  }

  void initControllers(int length) {
    animationControllers.clear();
    for (var i = 0; i < length; i++) {
      animationControllers.add(
        AnimationController(
          vsync: this,
          value: 1,
          duration: const Duration(milliseconds: 500),
        ),
      );
      animationControllers[i].forward();
    }
  }

  @override
  void didUpdateWidget(_List oldWidget) {
    print(oldWidget.list.length);
    if (animationControllers.length != widget.list.length) {
      animationControllers.add(
        AnimationController(
          vsync: this,
          duration: const Duration(milliseconds: 500),
        ),
      );
      animationControllers.last.forward();
    }
    super.didUpdateWidget(oldWidget);
  }

  Future<void> onDelete(int index) async {
    await animationControllers[index].reverse();
    animationControllers[index].dispose();
    widget.onDelete(index);
    animationControllers.removeAt(index);
  }

  @override
  Widget build(BuildContext context) {
    return ListView.builder(
      itemCount: widget.list.length,
      itemBuilder: (context, index) {
        return SizeTransition(
          sizeFactor: animationControllers[index],
          child: ListTile(
            title: Text(widget.list[index]),
            trailing: IconButton(
              onPressed: () => onDelete(index),
              icon: Icon(Icons.delete),
            ),
          ),
        );
      },
    );
  }
}