RainMakerFirstTry.dart

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

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

class TempScreen extends StatefulWidget {
  @override
  _TempScreenState createState() => _TempScreenState();
}

class _TempScreenState extends State<TempScreen> with TickerProviderStateMixin {
  
  AnimationController _controller;
  Animation<Offset> _offsetFloat;
  int counter = 0;
  double dx = 200;
  Random rgn = Random();

  @override
  void initState() {
    super.initState();

    _controller = AnimationController(
      vsync: this,
      duration: const Duration(seconds: 5),
    );

    _offsetFloat = Tween<Offset>(
            begin: Offset(0.0, 0.0),
            end: Offset(0.0, 2.0)) // slide vertical transition
        .animate(CurvedAnimation(
      parent: _controller,
      curve: Curves.easeInOutQuint, // matches to the rain like simulation
    ));
    _controller.forward(); // starts the animation
    
   _controller.repeat(reverse: false);  // will repeat forever
    
    // below code is to stop it from repeating forever 
//     TickerFuture tickerFuture = _controller.repeat(reverse: false);

//     tickerFuture.timeout(
//         Duration(
//             seconds: 5 *
//                 3 // here the 2nd varaible decides for how many times it will repeat
//             ), onTimeout: () {
//       _controller.forward(from: 0); // stops at the starting position
//       _controller.stop(canceled: true);
//     });
  }

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

  @override
  Widget build(BuildContext context) {
    MediaQueryData mediaQuery = MediaQuery.of(context);
    return Scaffold(
      backgroundColor: Colors.grey,
      // appBar: AppBar(
      //   title: Text('Line'),
      // ),
      body: Stack(
        children: [
          SlideTransition(
            position: _offsetFloat,
            child: CustomPaint(
              painter: RainPainter(
                counter: counter,
                dx: dx,
              ),
              child: Container(),
            ),
          ),
          Align(
            child: Text(' the counter is: $counter'),
          ),
          Align(
            alignment: Alignment.bottomCenter,
            child: RaisedButton(
                child: Text('Add counter'),
                onPressed: () {
                  paintMoreLines(mediaQuery.size.width);
                  // });
                }),
          ),
        ],
      ),
    );
  }

  void paintMoreLines(double width) {
    setState(() {
      counter++;
      print('counter fnc: $counter');
      for (int i = 0; i < counter; i++) {
        // if (dx < 0 || dx > width) {
          dx = rgn.nextDouble() * width;
          print('value of dx : $dx');
        // }
      }
    });
  }
}

class RainPainter extends CustomPainter {
  final int counter;
  final double dx;

  RainPainter({@required this.dx, @required this.counter});
  @override
  void paint(Canvas canvas, Size size) {
    Paint _paint = Paint()
      ..color = Colors.blue
      ..strokeWidth = 8.0;

    for (int i = 0; i < counter; i++) {
      canvas.drawLine(Offset(dx, -45), Offset(dx, 25), _paint);
      // print('i - $i');
    }

    // the 'dy' element of offset, remains the same
    // the 'dx' is element, which will be changed randomly
  }

  @override
  bool shouldRepaint(covariant CustomPainter oldDelegate) {
    return true;
  }
}