Sliver App Bar In Flutter

UserInterface:

Code:

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


void main() => runApp(
      MaterialApp(
        title: "Sliver App bar",
        debugShowCheckedModeBanner: false,
        home: sliver_appbar(),
      ),
    );

class sliver_appbar extends StatelessWidget {
  //const sl({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: CustomScrollView(
        slivers: [
          SliverAppBar(
            backgroundColor: Colors.greenAccent,
            expandedHeight: 200,
            title: Text('Flexible App Bar'),
            centerTitle: true,
            floating: true,
            pinned: true,
            leading: Icon(Icons.arrow_back),
            actions: [
              Icon(Icons.settings),
              SizedBox(width: 12),
            ],
            flexibleSpace: FlexibleSpaceBar(
              background: Image.network(
                  'https://images.unsplash.com/photo-1629732676198-fe5cd0933cfd?ixid=MnwxMjA3fDB8MHxwaG90by1wYWdlfHx8fGVufDB8fHx8&ixlib=rb-1.2.1&auto=format&fit=crop&w=346&q=80',
                  fit: BoxFit.cover),
            ),
          ),
          SliverToBoxAdapter(
            child: GridView.builder(
              gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
                crossAxisCount: 2,
              ),
              primary: false,
              shrinkWrap: true,
              itemCount: 20,
              itemBuilder: (Context, index) => Container(
                child: Image.network(
                    'https://images.unsplash.com/photo-1494145904049-0dca59b4bbad?ixid=MnwxMjA3fDB8MHxzZWFyY2h8OHx8YnVpbGRpbmdzfGVufDB8fDB8fA%3D%3D&ixlib=rb-1.2.1&auto=format&fit=crop&w=500&q=60',
                    fit: BoxFit.cover),
              ),
            ),
          ),
        ],
      ),
    );
  }
}