explicit_animation_v2.dart

import 'package:flutter/material.dart';

class Home extends StatefulWidget {
  const Home({ super.key });

  @override
  State<Home> createState() => _HomeState();
}

class _HomeState extends State<Home> with SingleTickerProviderStateMixin {
  double currentOpacity = 1.0;
  double targetOpacity = 1.0;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: TweenAnimationBuilder<double>(
          tween: Tween<double>(begin: currentOpacity, end: targetOpacity),
          duration: Duration(milliseconds: 400),
          builder: (BuildContext context, double opacity, Widget? child) {
            currentOpacity = opacity;
            return Opacity(
              opacity: opacity,
              child: child,
            );
          },
          child: ElevatedButton(
            onPressed: () {
              setState(() { targetOpacity -= 0.2; });
            },
            child: Text('Press Me'),
          ),
        ),
      ),
    );
  }
}

void main() {
  runApp(
    MaterialApp(
      theme: ThemeData.light(useMaterial3: true),
      home: Home(),
    ),
  );
}