Animate elements in ListView on initialization - flutter

Question

I want to achieve something like below (animation style doesn't matter, I'm looking for the way to do this)
However, all resources and question only explain how to create
item addition or removal animations.
My current code (I use BLoC pattern)
class _MembersPageState extends State<MembersPage> {
#override
Widget build(BuildContext context) {
return BlocProvider<MembersPageBloc>(
create: (context) =>
MembersPageBloc(userRepository: UserRepository.instance)..add(MembersPageShowed()),
child: BlocBuilder<MembersPageBloc, MembersPageState>(
builder: (context, state) {
if (state is MembersPageSuccess) {
return ListView.builder(
itemCount: state.users.length,
itemBuilder: (context, index) {
User user = state.users[index];
return ListTile(
isThreeLine: true,
leading: Icon(Icons.person, size: 36),
title: Text(user.name),
subtitle: Text(user.username),
onTap: () => null,
);
},
);
} else
return Text("I don't care");
},
),
);
}
}

Answer 1

Widgets like AnimatedOpacity and AnimatedPositioned can be used to achieve this. However, lifecycle of the children widgets in a ListView is a bit complex. They get destroyed and recreated according to the scroll position. If the child widget has an animation that starts on initialization, it will reanimate whenever the child gets visible to the UI.
Here is my hacky solution. I used a static boolean to indicate whether it's the first time or recreation state and simply ignore the recration. You can copy and try it in Dartpad.
import 'package:flutter/material.dart';
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
backgroundColor: Colors.brown,
body: ListView(
children: List.generate(
25,
(i) => AnimatedListItem(i, key: ValueKey<int>(i)),
),
),
),
);
}
}
class AnimatedListItem extends StatefulWidget {
final int index;
const AnimatedListItem(this.index, {Key? key}) : super(key: key);
#override
State<AnimatedListItem> createState() => _AnimatedListItemState();
}
class _AnimatedListItemState extends State<AnimatedListItem> {
bool _animate = false;
static bool _isStart = true;
#override
void initState() {
super.initState();
if (_isStart) {
Future.delayed(Duration(milliseconds: widget.index * 100), () {
setState(() {
_animate = true;
_isStart = false;
});
});
} else {
_animate = true;
}
}
#override
Widget build(BuildContext context) {
return AnimatedOpacity(
duration: const Duration(milliseconds: 1000),
opacity: _animate ? 1 : 0,
curve: Curves.easeInOutQuart,
child: AnimatedPadding(
duration: const Duration(milliseconds: 1000),
padding: _animate
? const EdgeInsets.all(4.0)
: const EdgeInsets.only(top: 10),
child: Container(
constraints: const BoxConstraints.expand(height: 100),
child: Card(
child: Padding(
padding: const EdgeInsets.all(8.0),
child: Text(
widget.index.toString(),
style: const TextStyle(fontSize: 24),
),
),
),
),
),
);
}
}

Answer 2

I created a gist on dartpad shows how to add initial animation for ListView
The key point is to create an AnimationController for each list item, cache it, and clean up when animation is complete.