How to change row/column states with animation in Flutter?

Question

I am using rows and columns in my layout and load some data from the internet to display information inside my rows and columns.

I want to design a dynamic loading page in such a way that every loaded data makes a particular widget visible with an animation (by moving the other widgets around smoothly).

I am currently using if clauses inside my layouts and calling setState() when new data is retrieved.

Column(
  children: [
    SomeWidget(),
    if (data != null)
      DataWidget(),
    AnotherWidget(),
  ],
),

How can I insert widgets between other widgets in rows/columns with animation after some data is retrieved?

Solution

Flutter already has tons of useful widgets which you can use for this implementation. I believe that the AnimatedList widget solves your problem. I have added the widget of the week video and a basic example below.

Widget of the Week - AnimatedList

Example:

import 'package:flutter/material.dart';

class PageOne extends StatefulWidget {
  @override
  _PageOneState createState() => _PageOneState();
}

class _PageOneState extends State<PageOne> {
  /// The global key to access the animated list.
  final _animatedListKey = GlobalKey<AnimatedListState>();

  List<String> _items = [];

  @override
  void initState() {
    // Set the items that should be display.
    _items = ['A', 'B', 'D', 'E', 'F'];
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Example')),
      body: AnimatedList(
        key: _animatedListKey,
        initialItemCount: _items.length,
        itemBuilder: (context, index, animation) {
          return SlideTransition(
            position: animation.drive(
              // Tween that slides from right to left.
              Tween(begin: Offset(1.0, 0.0), end: Offset(0.0, 0.0)),
            ),
            // Simply display the letter.
            child: ListTile(title: Text(_items[index])),
          );
        },
      ),
      floatingActionButton: FloatingActionButton(
        child: Icon(Icons.add),
        onPressed: () {
          // The item to insert.
          final _item = 'C';

          // Add, sort, and retrieve the index of the inserted item.
          List<String> _temp = _items..add(_item);
          _temp.sort();
          final _index = _temp.indexOf(_item);

          // Update the state and start the animated list animation.
          setState(() {
            _items.insert(_index, _item);
            _animatedListKey.currentState?.insertItem(_index);
          });
        },
      ),
    );
  }
}

Comments

[rasitayaz]

But isn't AnimatedSwitcher for switching between two different widgets? I want my widgets to appear out of nowhere. Is there a better practice for this or do I need to set AnimatedSwitcher's child as an empty Container and then switch it to the widget I want?

[Jim]

I've edited my answer, is this what you want? flutter_staggered_animations

[rasitayaz]

Thank you, this is probably the best approach for me. But do you know any way to insert list items by giving them some priority? For example, I want item C to be placed before D, E and after A, B. The problem is that the available items in the list may vary when C arrives.

[Admin]

Yes that is certainly possible! I have added a basic implementation of what you are asking. Let me know if anything is unclear.