import 'package:flutter/material.dart';

void main() {
  runApp(
    MaterialApp(
      home: MyWidget(),
    ),
  );
}

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

  @override
  State<MyWidget> createState() => _MyWidgetState();
}

class _MyWidgetState extends State<MyWidget> {
  bool playAnime = true;
  
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            AnimatedCrossFade(
              firstChild: Container(
                width: 200,
                height: 300,
                color: Colors.pink,
              ),
              secondChild: Container(
                width: 300,
                height: 200,
                color: Colors.orange,
              ),
              crossFadeState: playAnime
                  ? CrossFadeState.showFirst
                  : CrossFadeState.showSecond,
              duration: const Duration(
                milliseconds: 500,
              ),
            ),
            TextButton(
              onPressed: () => setState(() => playAnime = !playAnime),
              child: const Text('アニメション再生'),
            ),
          ],
        ),
      ),
    );
  }
}