Sliver : 스크롤 및 리스트 렌더링

Using slivers to achieve fancy scrolling

Where to find information on using slivers to implement fancy scrolling effects, like elastic scrolling, in Flutter.

https://docs.flutter.dev/ui/layout/scrolling/slivers

1. Sliver

• 스크롤 가능한 위젯의 일종

• 효율적인 스크롤 및 리스트 렌더링을 위해 사용되는 독특한 디자인 패턴

• 리스트의 각 아이템을 개별적으로 렌더링하고 스크롤 이벤트를 처리하는 데 최적화

• CustomScrollView 위젯과 함께 사용되는 경우 매우 효율적인 리스트 렌더링 제공

• 내부에도 모두 Sliver 를 사용해야 함

height: MediaQuery.of(context).size.height // 전체 화면 높이
      - MediaQuery.of(context).padding.top // 상태바 높이
      - _appBar.preferredSize.height // 앱바 높이
      - 16 // 텍스트 높이
      - 48 // 버튼 높이

2. SliverList / SliverGrid

• gridDelegate를 이용해서 그리드 레이아웃 정의

• 매 index마다 itemBuilder가 생성된 그리드 반환

  SliverGrid(
    gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
      crossAxisCount: 2,
      childAspectRatio: 1.0,
    ),
    delegate: SliverChildBuilderDelegate(
          (context, index) {
        return Card(
          child: Container(
            color: Colors.blue[index % 9 * 100],
            child: Center(
              child: Text('Grid Item $index'),
            ),
          ),
        );
      },
      childCount: 20,
    ),
  ),

3. SliverChildListDelegate : 일반적인 위젯 리스트→ SliverList

  SliverList(
    delegate: SliverChildListDelegate(
      [
        Container(
          child: Image(image: NetworkImage('https://picsum.photos/id/1/200/300'),fit: BoxFit.cover),
        ),
        SizedBox(height: 10,),
        Container(
          child: Image(image: NetworkImage('https://picsum.photos/id/2/200/300'),fit: BoxFit.cover),
        ),
        SizedBox(height: 10,),
        Container(
          child: Image(image: NetworkImage('https://picsum.photos/id/3/200/300'),fit: BoxFit.cover),
        ),
      ]
    ),
  ),

4. SliverChildBuilderDelegate

• ListView.builder나 GridView.builder와 유사한 방식으로 작동

• 매 index마다 itemBuilder 콜백을 사용하여 슬리버에 대한 자식을 반환

• 동적인 리스트나 그리드를 쉽게 생성

  SliverList(
    delegate: SliverChildBuilderDelegate(
      childCount: 10,
      (context, index) =>
        Padding(
          padding: const EdgeInsets.symmetric(vertical: 5.0),
          child: Image.network("https://picsum.photos/id/${index}/200/300",
          fit: BoxFit.contain,),
        ),
    )
  ),

5. ListView.builder / List.generate

• List.generate : 미리 전체 아이템 리스트를 생성 / 메모리 많이 사용

• ListView.builder : lazy loading기법을 사용하여 리스트 뷰 아이템이 필요할 때만 생성하고 화면에 표시

• itemBuilder : 콜백함수를 이용해서 아이템이 필요할 때만 생성 / 대규모 데이터 처리에 효율적

6. CustomScrollView : 조금 더 세부적인 ScrollView

• snap과 floating옵션 : 위아래로 살짝만 스크롤해도 SliverAppBar가 화면에 나타나고 사라짐

• pinned 옵션 : 스크롤을 올리더라도 앱바가 화면에서 사라지지 않음

• expandedHeight : 앱바의 크기를 지정 / 기본값은 60

• flexibleSpace : 유연한 공간을 제공하여 다양한 콘텐츠를 넣을수 있음

class HomePage extends StatelessWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: CustomScrollView(
        slivers: [
          SliverAppBar(
            snap: true,
            floating: true,
            title: Text("SliverAppBar"),
            pinned: false,

            expandedHeight: 250,
            flexibleSpace: FlexibleSpaceBar(
              title: Text("제목"),
              centerTitle: true,
              background: Image.network(
                'https://picsum.photos/200/300',
                fit: BoxFit.cover,
              ),
            ),

          const SliverAppBar(
            title: Text("pinned"),
            pinned: true,
            centerTitle: true,
          ),

7. SliverToBoxAdapter

     SliverToBoxAdapter(
       child: Container(
       height: 200,
       child: ListView.builder(
         scrollDirection: Axis.horizontal, // 가로 스크롤
         itemCount: 7,
         itemBuilder: (BuildContext context, int index) {
           return Image(
               image: AssetImage("assets/다운로드 (${index + 1}).jpg"));
         },
       ),
     )),

8. SliverFixedExtentList

      SliverFixedExtentList(
          itemExtent: 100, // 내부 요소의 크기 무시
          delegate: SliverChildBuilderDelegate( // 계산이 필요하면 빌더를 사용
            (context, index) {
              if (index % 4 == 0 && index != 0)
                return Ad(((index / 4) - 1).toInt());
              return Diary(index);
            },
          )),
        ],
      ),
    );
  }

9. SliverFillViewport

  SliverFillViewport(
    delegate: SliverChildBuilderDelegate(
      childCount: 10,
      (context, index) {
        return Card(
          child: Container(
            color: Colors.blue[index % 9 * 100],
            child: Center(
              child: Text('Fill Viewport Item $index'),
            ),
          ),
        );
      },
    ),
  ),

10. SliverFillRemaining : 남은 공간을 채우기 위한 View 생성

  // 위에 있는 Sliver,
  SliverFillRemaining(
    child: Center(
      child: Text('This is the remaining content.'),
    ),
  ),

11. SliverPersistentHeader : 앱에서 항상 표시되는 헤더

 SliverPersistentHeader(
   pinned: false,
   floating : false,
   delegate: MySliverPersistentHeaderDelegate(
     minHeight: 50.0,
     maxHeight: 120.0,
     child: Container(
       color: Colors.blue[300],
       child: const Center(
         child: Text(
           'SliverPersistentHeader',
           style: TextStyle(color: Colors.white, fontSize: 20),
         ),
       ),
     ),
   ),
 ),

• minHeight : 작은 값으로 축소된 헤더의 크기를 지정할 때 사용 / pinned: true일때 유효

pinned: true일때

• floating : false : 가장 상단으로 올라가야 내려옴

• floating : true : 스크롤을 하자마자 헤더가 내려옴

• SliverPersistentHeaderDelegate를 상속 -> 필요한 메소드와 속성 사용 헤더의 크기와 위치를 동적 조정 가능

class MySliverPersistentHeaderDelegate extends SliverPersistentHeaderDelegate {
  MySliverPersistentHeaderDelegate({
    required this.minHeight,
    required this.maxHeight,
    required this.child,
  });

  final double minHeight;
  final double maxHeight;
  final Widget child;

  @override
  Widget build(
      BuildContext context, double shrinkOffset, bool overlapsContent) {
    return SizedBox.expand(child: child);
  }

  @override
  double get maxExtent => maxHeight;

  @override
  double get minExtent => minHeight;

  @override
  bool shouldRebuild(covariant MySliverPersistentHeaderDelegate oldDelegate) {
    return maxHeight != oldDelegate.maxHeight ||
        minHeight != oldDelegate.minHeight ||
        child != oldDelegate.child;
  }
}

pinned false일때

## 상단 PersistenceHeader pinned false 적용

![Untitled](https://prod-files-secure.s3.us-west-2.amazonaws.com/a21638a1-cc1f-4c5f-be54-d65c3bb6a357/df6d4704-c9be-4873-be3b-b30f71602a71/Untitled.png)

![Untitled](https://prod-files-secure.s3.us-west-2.amazonaws.com/a21638a1-cc1f-4c5f-be54-d65c3bb6a357/76a418db-1f32-4785-8c99-3332b62d193c/Untitled.png)

```dart
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(useMaterial3: true, colorSchemeSeed: Colors.purple),
      home: HomePage(),
    );
  }
}

class HomePage extends StatelessWidget {
  const HomePage({super.key});

  @override
  Widget build(BuildContext context) {
    return DefaultTabController(
      length: 3,
      child: Scaffold(
        appBar: AppBar(
          title: Text("Kurly"),
        ),
        body: HomeBody(),
      ),
    );
  }
}

class HomeBody extends StatelessWidget {
  const HomeBody({super.key});

  @override
  Widget build(BuildContext context) {
    return NestedScrollView(
      headerSliverBuilder: (context, innerBoxIsScrolled) {
        return [
          SliverPersistentHeader(delegate: TabBarDelegate(), pinned: false)
        ];
      },
      body: TabBarView(
        children: [
          ScreenA(),
          Container(color: Colors.blue),
          Container(color: Colors.yellow),
        ],
      ),
    );
  }
}

class ScreenA extends StatelessWidget {
  const ScreenA({
    super.key,
  });

  @override
  Widget build(BuildContext context) {
    return CustomScrollView(
      slivers: [
        SliverToBoxAdapter(
          child: Container(
            height: 300,
            color: Colors.greenAccent,
          ),
        ),
        SliverPersistentHeader(delegate: CategoryBreadcrumbs(), pinned: true),
        SliverList(
          delegate: SliverChildBuilderDelegate(
            childCount: 40,
            (context, index) {
              return Container(
                height: 40,
                // 보는 재미를 위해 인덱스에 아무 숫자나 곱한 뒤 255로
                // 나눠 다른 색이 보이도록 함.
                color: Color.fromRGBO(
                    (index * 45) % 255, (index * 70) % 255, (index * 25), 1.0),
              );
            },
          ),
        ),
      ],
    );
  }
}

class CategoryBreadcrumbs extends SliverPersistentHeaderDelegate {
  const CategoryBreadcrumbs();

  @override
  Widget build(
      BuildContext context, double shrinkOffset, bool overlapsContent) {
    return Container(
      color: Colors.white,
      height: 48,
      padding: const EdgeInsets.symmetric(horizontal: 16.0),
      child: Row(
        children: [
          const Text("총 239개", style: TextStyle(color: Colors.black)),
          const Spacer(),
          TextButton(
            onPressed: () {},
            child: const Center(child: Text("필터")),
          )
        ],
      ),
    );
  }

  @override
  double get maxExtent => 48;

  @override
  double get minExtent => 48;

  @override
  bool shouldRebuild(covariant SliverPersistentHeaderDelegate oldDelegate) {
    return false;
  }
}

class TabBarDelegate extends SliverPersistentHeaderDelegate {
  const TabBarDelegate();

  @override
  Widget build(
      BuildContext context, double shrinkOffset, bool overlapsContent) {
    return TabBar(
      tabs: [
        Tab(child: Text("컬리추천")),
        Tab(child: const Text("신상품")),
        Tab(child: const Text("베스트")),
      ],
    );
  }

  @override
  double get maxExtent => 48;

  @override
  double get minExtent => 48;

  @override
  bool shouldRebuild(covariant SliverPersistentHeaderDelegate oldDelegate) {
    return false;
  }
}
```

첫번째 방법 Scaffold에 appbar와 tabbar 두기

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

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(useMaterial3: true, colorSchemeSeed: Colors.purple),
      home: HomePage(),
    );
  }
}

class HomePage extends StatelessWidget {
  const HomePage({super.key});

  @override
  Widget build(BuildContext context) {
    return DefaultTabController(
      length: 3,
      child: Scaffold(
        appBar: AppBar(
          title: Text("Kurly"),
          bottom: TabBar(
            tabs: [
              Tab(child: Text("컬리추천")),
              Tab(child: const Text("신상품")),
              Tab(child: const Text("베스트")),
            ],
          ),
        ),
        body: HomeBody(),
      ),
    );
  }
}

class HomeBody extends StatelessWidget {
  const HomeBody({super.key});

  @override
  Widget build(BuildContext context) {
    return CustomScrollView(
      slivers: [
        SliverFillRemaining(
          child: TabBarView(
            children: [
              ScreenA(),
              Container(color: Colors.blue),
              Container(color: Colors.yellow),
            ],
          ),
        ),
      ],
    );
  }
}

class ScreenA extends StatelessWidget {
  const ScreenA({
    super.key,
  });

  @override
  Widget build(BuildContext context) {
    return CustomScrollView(
      slivers: [
        SliverToBoxAdapter(
          child: Container(
            height: 300,
            color: Colors.greenAccent,
          ),
        ),
        SliverPersistentHeader(delegate: CategoryBreadcrumbs(), pinned: true),
        SliverList(
          delegate: SliverChildBuilderDelegate(
            childCount: 40,
            (context, index) {
              return Container(
                height: 40,
                // 보는 재미를 위해 인덱스에 아무 숫자나 곱한 뒤 255로
                // 나눠 다른 색이 보이도록 함.
                color: Color.fromRGBO(
                    (index * 45) % 255, (index * 70) % 255, (index * 25), 1.0),
              );
            },
          ),
        ),
      ],
    );
  }
}

class CategoryBreadcrumbs extends SliverPersistentHeaderDelegate {
  const CategoryBreadcrumbs();

  @override
  Widget build(
      BuildContext context, double shrinkOffset, bool overlapsContent) {
    return Container(
      color: Colors.white,
      height: 48,
      padding: const EdgeInsets.symmetric(horizontal: 16.0),
      child: Row(
        children: [
          const Text("총 239개", style: TextStyle(color: Colors.black)),
          const Spacer(),
          TextButton(
            onPressed: () {},
            child: const Center(child: Text("필터")),
          )
        ],
      ),
    );
  }

  @override
  double get maxExtent => 48;

  @override
  double get minExtent => 48;

  @override
  bool shouldRebuild(covariant SliverPersistentHeaderDelegate oldDelegate) {
    return false;
  }
}

두번째 방법 Column + Expanded

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

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(useMaterial3: true, colorSchemeSeed: Colors.purple),
      home: HomePage(),
    );
  }
}

class HomePage extends StatelessWidget {
  const HomePage({super.key});

  @override
  Widget build(BuildContext context) {
    return DefaultTabController(
      length: 3,
      child: Scaffold(
        appBar: AppBar(
          title: Text("Kurly"),
        ),
        body: HomeBody(),
      ),
    );
  }
}

class HomeBody extends StatelessWidget {
  const HomeBody({super.key});

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        TabBar(
          tabs: [
            Tab(child: Text("컬리추천")),
            Tab(child: const Text("신상품")),
            Tab(child: const Text("베스트")),
          ],
        ),
        Expanded(
          child: TabBarView(
            children: [
              ScreenA(),
              Container(color: Colors.blue),
              Container(color: Colors.yellow),
            ],
          ),
        ),
      ],
    );
  }
}

class ScreenA extends StatelessWidget {
  const ScreenA({
    super.key,
  });

  @override
  Widget build(BuildContext context) {
    return CustomScrollView(
      slivers: [
        SliverToBoxAdapter(
          child: Container(
            height: 300,
            color: Colors.greenAccent,
          ),
        ),
        SliverPersistentHeader(delegate: CategoryBreadcrumbs(), pinned: true),
        SliverList(
          delegate: SliverChildBuilderDelegate(
            childCount: 40,
            (context, index) {
              return Container(
                height: 40,
                // 보는 재미를 위해 인덱스에 아무 숫자나 곱한 뒤 255로
                // 나눠 다른 색이 보이도록 함.
                color: Color.fromRGBO(
                    (index * 45) % 255, (index * 70) % 255, (index * 25), 1.0),
              );
            },
          ),
        ),
      ],
    );
  }
}

class CategoryBreadcrumbs extends SliverPersistentHeaderDelegate {
  const CategoryBreadcrumbs();

  @override
  Widget build(
      BuildContext context, double shrinkOffset, bool overlapsContent) {
    return Container(
      color: Colors.white,
      height: 48,
      padding: const EdgeInsets.symmetric(horizontal: 16.0),
      child: Row(
        children: [
          const Text("총 239개", style: TextStyle(color: Colors.black)),
          const Spacer(),
          TextButton(
            onPressed: () {},
            child: const Center(child: Text("필터")),
          )
        ],
      ),
    );
  }

  @override
  double get maxExtent => 48;

  @override
  double get minExtent => 48;

  @override
  bool shouldRebuild(covariant SliverPersistentHeaderDelegate oldDelegate) {
    return false;
  }
}

class TabBarDelegate extends SliverPersistentHeaderDelegate {
  const TabBarDelegate();

  @override
  Widget build(
      BuildContext context, double shrinkOffset, bool overlapsContent) {
    return TabBar(
      tabs: [
        Tab(child: Text("컬리추천")),
        Tab(child: const Text("신상품")),
        Tab(child: const Text("베스트")),
      ],
    );
  }

  @override
  double get maxExtent => 48;

  @override
  double get minExtent => 48;

  @override
  bool shouldRebuild(covariant SliverPersistentHeaderDelegate oldDelegate) {
    return false;
  }
}

Flutter로 Shopping 앱 만들기 — 3 NestedScrollView

첫 글 보러가기

https://medium.com/@honor-driven/flutter로-shopping-앱-만들기-3-nestedscrollview-cec18854f859

Flutter로 Shopping 앱 만들기 — 3 NestedScrollView

첫 글 보러가기

https://medium.com/@honor-driven/flutter로-shopping-앱-만들기-3-nestedscrollview-cec18854f859

Flutter로 Shopping 앱 만들기 — 3 NestedScrollView

첫 글 보러가기

https://medium.com/@honor-driven/flutter로-shopping-앱-만들기-3-nestedscrollview-cec18854f859

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

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: HomePage(),
    );
  }
}

class HomePage extends StatelessWidget {
  const HomePage({super.key});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: CustomScrollView(
        slivers: [
          SliverAppBar(
            title: Text("앱바"),
            pinned: false,
            //snap: true,
            //floating: true,
            expandedHeight: 250,
            flexibleSpace: Container(
              color: Colors.green,
            ),
          ),
          SliverToBoxAdapter(
            child: Container(
              color: Colors.red,
              height: 300,
            ),
          ),
          SliverToBoxAdapter(
            child: SizedBox(
              height: 100,
              child: ListView.builder(
                scrollDirection: Axis.horizontal,
                itemCount: 30,
                itemBuilder: (context, index) {
                  return Container(
                    width: 50,
                    color: Colors.yellow[((index % 9) + 1) * 100], // 0 ~ 8
                  );
                },
              ),
            ),
          ),
          SliverList(
            delegate: SliverChildBuilderDelegate(
              childCount: 20,
              (context, index) {
                return Container(
                  height: 50,
                  color: Colors.blue[((index % 9) + 1) * 100], // 0 ~ 8
                );
              },
            ),
          ),
        ],
      ),
    );
  }
}

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: HomePage(),
    );
  }
}

class HomePage extends StatelessWidget {
  const HomePage({super.key});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: CustomScrollView(
        slivers: [
          SliverAppBar(
            //반응하는 앱바
            title: Text("앱바"),
            pinned: true, // 앱바 고정
            // pinned: false, // 앱바 사라짐
            // snap: true,
            // //손가락으로 튕구다
            // floating: true,
            expandedHeight: 250,
            flexibleSpace: Container(
              color: Colors.green,
            ),
          ),
          SliverToBoxAdapter(
            child: Container(
              color: Colors.red,
              height: 300,
            ),
          ),
          SliverPersistentHeader(delegate: )
          SliverList(
            // 특정 타이밍에 자식의 스크롤을 무력화 시킨다. 포문 돌리면서 넣는거
            delegate: SliverChildBuilderDelegate(
              childCount: 20,
                  (context, index) {
                return Container(
                  color: Colors.yellow[((index % 9) + 1) * 100], //0~8
                  height: 50,
                );
              },
            ),
          ),
          SliverList(
            // 특정 타이밍에 자식의 스크롤을 무력화 시킨다. 포문 돌리면서 넣는거
            delegate: SliverChildBuilderDelegate(
              childCount: 20,
                  (context, index) {
                return Container(
                  color: Colors.blue[((index % 9) + 1) * 100], //0~8
                  height: 50,
                );
              },
            ),
          )
        ],
      ),
    );
  }
}

class MyPersistentHeaderDelegate extends SliverPersistentHeaderDelegate {
  final double minHeight;
  final double maxHeight;

  MyPersistentHeaderDelegate({
    required this.minHeight,
    required this.maxHeight,
  });

  @override
  Widget build(BuildContext context, double shrinkOffset,
      bool overlapsContent) {
    return Container(
      color: Colors.blueGrey,
      child: Center(
        child: Text(
          'SliverPersistentHeader',
          style: TextStyle(fontSize: 20.0, color: Colors.white),
        ),
      ),
    );
  }

  @override
  double get maxExtent => maxHeight;

  @override
  double get minExtent => minHeight;

  @override
  bool shouldRebuild(covariant SliverPersistentHeaderDelegate oldDelegate) {
    return true;
  }
}

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: HomePage(),
    );
  }
}

class HomePage extends StatelessWidget {
  const HomePage({super.key});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: CustomScrollView(
        slivers: [
          SliverAppBar(
            title: Text("Flutter Shopping App"),
            centerTitle: true,
            pinned: false,
          ),
          SliverAppBar(
            title: Text("앱바"),
            pinned: true,
            //snap: true,
            //floating: true,
            expandedHeight: 250,
            flexibleSpace: Container(
              color: Colors.green,
            ),
          ),
          SliverToBoxAdapter(
            child: Container(
              color: Colors.red,
              height: 300,
            ),
          ),
          SliverPersistentHeader(
            pinned: true,
            delegate: MyPersistentHeaderDelegate(
              child: Container(
                color: Colors.blueGrey,
                child: Center(
                  child: Text(
                    'SliverPersistentHeader',
                    style: TextStyle(fontSize: 20.0, color: Colors.white),
                  ),
                ),
              ),
              minHeight: 50,
              maxHeight: 500,
            ),
          ),
          SliverPersistentHeader(
            pinned: true,
            delegate: MyPersistentHeaderDelegate(
              child: ListView.builder(
                scrollDirection: Axis.horizontal,
                itemCount: 30,
                itemBuilder: (context, index) {
                  return Container(
                    width: 100,
                    color: Colors.yellow[((index % 9) + 1) * 100], // 0 ~ 8
                  );
                },
              ),
              minHeight: 100,
              maxHeight: 100,
            ),
          ),
          SliverList(
            delegate: SliverChildBuilderDelegate(
              childCount: 20,
              (context, index) {
                return Container(
                  height: 50,
                  color: Colors.blue[((index % 9) + 1) * 100], // 0 ~ 8
                );
              },
            ),
          ),
          SliverFillRemaining(
            // 마지막 남은 높이 계산
            child: Center(
              child: Text('This is the remaining content.'),
            ),
          ),
        ],
      ),
    );
  }
}

class MyPersistentHeaderDelegate extends SliverPersistentHeaderDelegate {
  final double minHeight;
  final double maxHeight;
  final Widget child;

  MyPersistentHeaderDelegate({
    required this.child,
    required this.minHeight,
    required this.maxHeight,
  });

  @override
  double get maxExtent => maxHeight;

  @override
  double get minExtent => minHeight;

  @override
  bool shouldRebuild(covariant SliverPersistentHeaderDelegate oldDelegate) {
    return true;
  }

  @override
  Widget build(
      BuildContext context, double shrinkOffset, bool overlapsContent) {
    return child;
  }
}