Flutter AnimatedSize works in one direction only

Question

I have got following code from https://medium.com/flutter-community/flutter-working-with-animatedsize-35253ff8f16a

it is using AnimatedSize, but animation works only while container is expanding and not while is it shirking. is this the default behavior? I want to animated while both expanding and shriking.

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Demo',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);
  final String title;

  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> with TickerProviderStateMixin {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  double _height = 80.0;
  double _width = 80.0;
  var _color = Colors.blue;
  bool _resized = false;
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      body: new Center(
        child: new Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            AnimatedSize(
              curve: Curves.easeIn,
              vsync: this,
              duration: new Duration(seconds: 1),
              child: new GestureDetector(
                onTap: () {
                  setState(() {
                    if (_resized) {
                      _resized = false;
                      _color = Colors.blue;
                      _height = 80.0;
                      _width = 80.0;
                    } else {
                      _resized = true;
                      _color = Colors.blue;
                      _height = 320.0;
                      _width = 320.0;
                    }
                  });
                },
                child: new Container(
                  width: _width,
                  height: _height,
                  color: _color,
                ),
              ),
            ),
          ],
        ),
      ),
    );
  }
}

Answer 1

AnimatedContainer is what you are looking for no need for AnimatedSize.

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);
  final String title;

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

class _MyHomePageState extends State<MyHomePage> with TickerProviderStateMixin {
  double _height = 80.0;
  double _width = 80.0;
  var _color = Colors.blue;
  bool _resized = false;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            GestureDetector(
              onTap: () {
                setState(() {
                  if (_resized) {
                    _resized = false;
                    _color = Colors.blue;
                    _height = 80.0;
                    _width = 80.0;
                  } else {
                    _resized = true;
                    _color = Colors.blue;
                    _height = 320.0;
                    _width = 320.0;
                  }
                });
              },
              child: AnimatedContainer(
                duration: Duration(seconds: 1),
                width: _width,
                height: _height,
                color: _color,
              ),
            ),
          ],
        ),
      ),
    );
  }
}

Or if you need AnimatedSize you can add a new container with the color as the AnimatedSize parent.

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);
  final String title;

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

class _MyHomePageState extends State<MyHomePage>
    with SingleTickerProviderStateMixin {
  double _height = 320.0;
  double _width = 320.0;
  var _color = Colors.blue;
  bool _resized = false;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: GestureDetector(
          onTap: () {
            setState(() {
              if (_resized) {
                _resized = false;
                _color = Colors.blue;
                _height = 80.0;
                _width = 80.0;
              } else {
                _resized = true;
                _color = Colors.blue;
                _height = 320.0;
                _width = 320.0;
              }
            });
          },
          child: Container(
            color: _color,
            child: AnimatedSize(
              curve: Curves.easeIn,
              vsync: this,
              duration: Duration(seconds: 1),
              child: Container(
                width: _width,
                height: _height,
              ),
            ),
          ),
        ),
      ),
    );
  }
}