explicit_animation.dart

import 'dart:ui' show lerpDouble;

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 {
  late AnimationController controller;
  double initialOpacity = 1.0;
  double targetOpacity = 1.0;

  @override
  void initState() {
    super.initState();
    controller = AnimationController(
      vsync: this,
      duration: Duration(milliseconds: 400),
    );
  }

  @override
  void dispose() {
    controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: AnimatedBuilder(
          animation: controller,
          builder: (BuildContext context, Widget? child) {
            final double opacity = lerpDouble(initialOpacity, targetOpacity, controller.value)!;
            return Container(
              padding: EdgeInsets.all(16),
              color: Colors.grey.withOpacity(opacity),
              child: TextButton(
                onPressed: () {
                  initialOpacity = opacity;
                  targetOpacity = initialOpacity - 0.2;
                  controller.value = 0;
                  controller.forward();
                },
                child: Text('Press Me'),
              ),
            );
          },
        ),
      ),
    );
  }
}

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