Flutter Raining Balls (Flutter Counter app Challenge 2020)

rainingballs.dart

// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'dart:math' as math;

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: Counter(),
    );
  }
}

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

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

class _CounterState extends State<Counter> with SingleTickerProviderStateMixin {
  @override
  void dispose() {
    // TODO: implement dispose
    super.dispose();
  }

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

  int counter = 0;
  late Size size;
  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    size = MediaQuery.of(context).size;
    return Scaffold(
      //   appBar: AppBar(),
      body: Stack(
        children: [
          Align(
              alignment: Alignment.center,
              child: Container(
                child: Text('$counter',
                    key: const Key('counter'),
                    style: const TextStyle(color: Colors.black, fontSize: 30)),
              )),
          for (int i = 0; i < counter; i++)
            Ball(
              size: size,
            )
        ],
      ),
      floatingActionButton: Row(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          const SizedBox(
            width: 30,
          ),
          FloatingActionButton(
              key: const Key('increment'),
              onPressed: _incrementCounter,
              tooltip: 'ball Animation',
              child: const Icon(Icons.radio_button_checked)),
        ],
      ),
    );
  }
}

class Ball extends StatefulWidget {
  const Ball({
    Key? key,
    required this.size,
  }) : super(key: key);
  final Size size;
  @override
  _BallState createState() => _BallState();
}

class _BallState extends State<Ball> with SingleTickerProviderStateMixin {
  late Animation<double> _ballAnimation;
  late AnimationController ballController;
  @override
  void initState() {
    super.initState();
    generateList();
    ballController = AnimationController(
      vsync: this,
      duration: const Duration(milliseconds: 4000),
    )..addListener(() {
        if (ballController.status == AnimationStatus.completed) {
          ballController.reset();
        }
      });
    _ballAnimation = Tween<double>(begin: widget.size.height + 100, end: 10).animate(
        CurvedAnimation(parent: ballController, curve: GravityCurve()));
    final index = math.Random().nextInt(positions.length);
    dx = positions[index];
    ballController.forward();
  }

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

  void generateList() {
    for (double i = -widget.size.width / 2;
        i < widget.size.width / 2;
        i += 50.0) {
      positions.add(i);
    }
  }

  Widget ball({double? size}) {
    return Container(
      height: size ?? 20,
      decoration: const BoxDecoration(color: Colors.red, shape: BoxShape.circle),
    );
  }

  double? dx;
  List<double> positions = [];
  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return AnimatedBuilder(
        animation: _ballAnimation,
        builder: (context, child) {
          return Transform.translate(
              offset: Offset(dx!, _ballAnimation.value), child: ball());
        });
  }
}

class GravityCurve extends Curve {
  // 0-1
  @override
  double transformInternal(double t) {
    return math.sin(math.pi * t);
    // return t < 0.5 ? sin(pi * t) : sin(3 * t * pi / 2);
  }
}