import 'package:flutter/material.dart';

class TestPage extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      /*
        Using LayoutBuilder to calculate the amount of
        items to print depending on screen height
      */
      home: LayoutBuilder(
        builder: (context, box)=>Scaffold(
          body: NestedScrollView(
            headerSliverBuilder: (context, innerScrolled)=>[
              SliverOverlapAbsorber(
                handle: NestedScrollView.sliverOverlapAbsorberHandleFor(context),
                child: SliverAppBar(
                  forceElevated: innerScrolled,
                  pinned: true,
                  title: Text("Printing ${(box.maxHeight/20).floor()} items"),
                ),
              ),
            ],
            body: Builder(
              builder: (context)=>CustomScrollView(
                slivers: <Widget>[
                  SliverOverlapInjector(
                    handle: NestedScrollView.sliverOverlapAbsorberHandleFor(context),
                  ),
                  SliverList(
                    delegate: SliverChildListDelegate(
                      [
                        for (var i=0; i<box.maxHeight/20; i++)
                          Text("Some text $i", style: TextStyle(fontSize: 20)),
                      ],
                    ),
                  ),
                ],
              ),
            ),
          ),
        ),
      ),
    );
  }

}