Animation on remove and on add widget - flutter

Question

I am trying to add animation to a list of widgets inside of a stack. When ever I remove a Widget or add a Widget to the List I Want to have a scale up/down transition as if the widget pops up from no where and shrinks to nothing. Any idea on how I can achieve this?

Answer 1

You can use AnimatedList widget as solution.
Example video here
Flutter documentation example
import 'package:flutter/material.dart';
void main() {
runApp(const AnimatedListSample());
}
class AnimatedListSample extends StatefulWidget {
const AnimatedListSample({super.key});
#override
State<AnimatedListSample> createState() => _AnimatedListSampleState();
}
class _AnimatedListSampleState extends State<AnimatedListSample> {
final GlobalKey<AnimatedListState> _listKey = GlobalKey<AnimatedListState>();
late ListModel<int> _list;
int? _selectedItem;
late int
_nextItem; // The next item inserted when the user presses the '+' button.
#override
void initState() {
super.initState();
_list = 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 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 CardItem(
animation: animation,
item: item,
// 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) {
_list.removeAt(_list.indexOf(_selectedItem!));
setState(() {
_selectedItem = null;
});
}
}
#override
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
appBar: AppBar(
title: const Text('AnimatedList'),
actions: <Widget>[
IconButton(
icon: const Icon(Icons.add_circle),
onPressed: _insert,
tooltip: 'insert a new item',
),
IconButton(
icon: const Icon(Icons.remove_circle),
onPressed: _remove,
tooltip: 'remove the selected item',
),
],
),
body: Padding(
padding: const EdgeInsets.all(16.0),
child: AnimatedList(
key: _listKey,
initialItemCount: _list.length,
itemBuilder: _buildItem,
),
),
),
);
}
}
typedef RemovedItemBuilder<T> = Widget Function(
T item, BuildContext context, Animation<double> animation);
/// 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> {
ListModel({
required this.listKey,
required this.removedItemBuilder,
Iterable<E>? initialItems,
}) : _items = List<E>.from(initialItems ?? <E>[]);
final GlobalKey<AnimatedListState> listKey;
final RemovedItemBuilder<E> 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);
}
/// 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({
super.key,
this.onTap,
this.selected = false,
required this.animation,
required this.item,
}) : assert(item >= 0);
final Animation<double> animation;
final VoidCallback? onTap;
final int item;
final bool selected;
#override
Widget build(BuildContext context) {
TextStyle textStyle = Theme.of(context).textTheme.headline4!;
if (selected) {
textStyle = textStyle.copyWith(color: Colors.lightGreenAccent[400]);
}
return Padding(
padding: const EdgeInsets.all(2.0),
child: SizeTransition(
sizeFactor: animation,
child: GestureDetector(
behavior: HitTestBehavior.opaque,
onTap: onTap,
child: SizedBox(
height: 80.0,
child: Card(
color: Colors.primaries[item % Colors.primaries.length],
child: Center(
child: Text('Item $item', style: textStyle),
),
),
),
),
),
);
}
}