【 Flutter 】Flutter を 基礎 から 学習 ( ウィジェット編 ) part114 アニメーション系ウィジェット

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';

void main() {
  runApp(new MaterialApp(home: new MyHomePage()));
}

class MyHomePage extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return _MyHomePageState();
  }
}

class _MyHomePageState extends State<MyHomePage> {
  var isVisible = false;

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'テスト中！',
      theme: ThemeData(primarySwatch: Colors.blue),
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        body: Center(
          child: AnimatedSwitcher(
            duration: Duration(seconds: 3),
            child: isVisible
                ? Container(
                    height: 100.0,
                    width: 100.0,
                    color: Colors.red.shade400,
                  )
                : const SizedBox.shrink(),
          ),
        ),
        floatingActionButton: FloatingActionButton(
          onPressed: () {
            setState(() {
              isVisible = !isVisible;
            });
          },
          child: Icon(Icons.add),
        ),
      ),
    );
  }
}

class MyWidget extends StatelessWidget {
  final ValueListenable<int> number;

  MyWidget(this.number);

  @override
  Widget build(BuildContext context) {
    return new Text(number.value.toString());
  }
}