Flutter animated list: animate entire list

Question

I am trying to implement Flutter's AnimatedList. What I'd like to achieve is to allready have a list of elements and then insert them one by one in the list with a total duration of 1 second.

For example: I have a list of 5 containers (a red one, a blue one, a green one, a pink one and a white one). I want each container to be slided in the list view.

I would now like that on startup, this list is displayed in the following timestamps:

0..200ms: red container

200..400ms: blue container

400..600ms: green container

600..800ms: pink container

800..1000ms: white container

Such that the entire list takes up 1 second to build and the amount of time 1 container should take for its animation is 1/nseconds and each container at index i in the list should start its animation at i*(1/n)seconds. Yet all documentation or examples I could find is simply displaying a button and then inserting a new item in the list, whilst I want an already created list to be displayed by the means of an animation.

Solution

Have you tried Timer.periodic.

You can simply use it and insert item after time time mentioned. like this :

void startTimer() {
  const oneSec = const Duration(milliseconds: 1000);
  _timer = new Timer.periodic(
    oneSec,
    (Timer timer) {
      _insert();
      if(_list.length == 10){
      timer.cancel();
      }
    },
  );

Complete code on Dart pad :

/// Flutter code sample for AnimatedList

// This sample application uses an [AnimatedList] to create an effect when
// items are removed or added to the list.
import 'dart:async';
import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';

void main() {
  runApp(const AnimatedListSample());
}

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

  @override
  _AnimatedListSampleState 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.

  Timer? _timer;
  @override
  void initState() {
    super.initState();
    _list = ListModel<int>(
      listKey: _listKey,
      initialItems: <int>[0, 1, 2],
      removedItemBuilder: _buildRemovedItem,
    );
    _nextItem = 3;
    startTimer();
  }

  void startTimer() {
  const oneSec = const Duration(milliseconds: 1000);
  _timer = new Timer.periodic(
    oneSec,
    (Timer timer) {
      _insert();
      if(_list.length == 10){
      timer.cancel();
      }
    },
  );
}
  
  @override
void dispose() {
  _timer!.cancel();
  super.dispose();
}

  // 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,
      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) {
      _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 = Widget Function(
    int 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 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(index, 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,
    this.onTap,
    this.selected = false,
    required this.animation,
    required this.item,
  })   : assert(item >= 0),
        super(key: key);

  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(
        axis: Axis.vertical,
        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),
              ),
            ),
          ),
        ),
      ),
    );
  }
}

You can customise that duration in startTimer method using any formulae u like. Remember the duration should be 200 milliseconds as you mentioned.

Comments

[Wouter Vandenputte]

Thanks, I already found a very similair approach myself also using timers.