GridView and Slider example

import 'package:flutter/material.dart';

void main() => runApp(MaterialApp(
    theme: ThemeData(primaryColor: Colors.tealAccent), home: new MyApp()));

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  double sliderValue = 1.0;
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.teal,
      appBar: AppBar(
        title: Slider(
          activeColor: Colors.red,
          min: 1.0,
          max: 3.0,
          onChanged: (double value) {
            setState(() {
              sliderValue = value;
            });
            print(sliderValue);
          },
          value: sliderValue,
        ),
      ),
      body: GridView.count(
        crossAxisCount: sliderValue.toInt(),
        childAspectRatio: 16.0 / (sliderValue * 10.0),
        children: <Widget>[
          Card(child: Center(child: Text("DATA"))),
          Card(child: Center(child: Text("DATA"))),
          Card(child: Center(child: Text("DATA"))),
          Card(child: Center(child: Text("DATA"))),
          Card(child: Center(child: Text("DATA"))),
          Card(child: Center(child: Text("DATA"))),
          Card(child: Center(child: Text("DATA"))),
          Card(child: Center(child: Text("DATA"))),
          Card(child: Center(child: Text("DATA"))),
        ],
      ),
    );
  }
}