medium_Flutter_Slider.dart

import 'package:flutter/material.dart';

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

class SliderApp extends StatefulWidget {
  @override
  _slider createState() => new _slider();
}

class _slider extends State<SliderApp> {

  double sliderVal = 3;
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: AppBar(
        title: new Text('Slider App'),
      ),
      body: new Center(
        child: new Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            new Slider(value: sliderVal, min: 1.0, max: 10.0, onChanged: (double dbVal){
              sliderMethod(dbVal);
            }),
            new Text('Slider value: $sliderVal')
          ],
        ),
      ),
    );
  }

  void sliderMethod(double dbVal) {
    setState(() {
      sliderVal = dbVal;
      print(dbVal);
    });
  }
}