import 'package:flutter/material.dart';
import 'package:get/get.dart';
import 'package:ftrecruiter/comm/utils/log_utils.dart';
import 'package:ftrecruiter/comm/widget/load_state_layout.dart';
import 'package:ftrecruiter/comm/widget/my_load_image.dart';
import 'package:ftrecruiter/modules/zdemo/page_four.dart';
import 'package:ftrecruiter/modules/zdemo/page_one.dart';
import 'package:ftrecruiter/modules/zdemo/page_three.dart';
import 'package:ftrecruiter/modules/zdemo/page_two.dart';

class DemoScroll1Page extends StatelessWidget {
  const DemoScroll1Page({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    final _tabs = <String>['猜你喜欢', '今日特价', '发现更多'];
    // 构建 tabBar
    return DefaultTabController(
      length: _tabs.length, // This is the number of tabs.
      child: Scaffold(
        body: NestedScrollView(
          headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
            return <Widget>[
              SliverOverlapAbsorber(
                handle: NestedScrollView.sliverOverlapAbsorberHandleFor(context),
                sliver: SliverAppBar(
                  title: const Text('商城'),
                  floating: false,
                  snap: false,
                  elevation: 0.0,
                  forceElevated: innerBoxIsScrolled,
                  pinned: true,
                ),
              ),
               SliverToBoxAdapter(
                child: Container(
                  alignment: Alignment.center,
                  width: double.infinity,
                  height: 191,
                  child: MyLoadImage("https://i04piccdn.sogoucdn.com/a35bde4b5756167a",width: 340, height: 191),
                ),
              ),
              SliverPersistentHeader(
                pinned: true,  // 固定在顶部
                delegate: SliverHeaderDelegate.fixedHeight( //固定高度
                  height: 50,
                  child: Container(
                    color: Colors.pink,
                    child: TabBar(
                      tabs: _tabs.map((String name) => Tab(text: name)).toList(),
                    ),
                  ),
                ),
              ),
            ];
          },
          body: TabBarView(
            children: _tabs.map((String name) {
              return Builder(
                builder: (BuildContext context) {
                  return CustomScrollView(
                    key: PageStorageKey<String>(name),
                    slivers: <Widget>[
                      SliverOverlapInjector(
                        handle: NestedScrollView.sliverOverlapAbsorberHandleFor(context),
                      ),
                      SliverPadding(
                        padding: const EdgeInsets.all(8.0),
                        sliver: buildSliverList(50),
                      ),
                    ],
                  );
                },
              );
            }).toList(),
          ),
        ),
      ),
    );
  }

  // 构建固定高度的SliverList，count为列表项属相
  Widget buildSliverList([int count = 5]) {
    return SliverFixedExtentList(
      itemExtent: 50,
      delegate: SliverChildBuilderDelegate(
        (context, index) {
          return ListTile(title: Text('$index'));
        },
        childCount: count,
      ),
    );
  }
}


typedef SliverHeaderBuilder = Widget Function(
    BuildContext context, double shrinkOffset, bool overlapsContent);
class SliverHeaderDelegate extends SliverPersistentHeaderDelegate {
  // child 为 header
  SliverHeaderDelegate({
    required this.maxHeight,
    this.minHeight = 0,
    required Widget child,
  })  : builder = ((a, b, c) => child),
        assert(minHeight <= maxHeight && minHeight >= 0);

  //最大和最小高度相同
  SliverHeaderDelegate.fixedHeight({
    required double height,
    required Widget child,
  })  : builder = ((a, b, c) => child),
        maxHeight = height,
        minHeight = height;

  //需要自定义builder时使用
  SliverHeaderDelegate.builder({
    required this.maxHeight,
    this.minHeight = 0,
    required this.builder,
  });

  final double maxHeight;
  final double minHeight;
  final SliverHeaderBuilder builder;

  @override
  Widget build(
      BuildContext context,
      double shrinkOffset,
      bool overlapsContent,
      ) {
    Widget child = builder(context, shrinkOffset, overlapsContent);
    //测试代码：如果在调试模式，且子组件设置了key，则打印日志
    assert(() {
      if (child.key != null) {
        print('${child.key}: shrink: $shrinkOffset，overlaps:$overlapsContent');
      }
      return true;
    }());
    // 让 header 尽可能充满限制的空间；宽度为 Viewport 宽度，
    // 高度随着用户滑动在[minHeight,maxHeight]之间变化。
    return SizedBox.expand(child: child);
  }

  @override
  double get maxExtent => maxHeight;

  @override
  double get minExtent => minHeight;

  @override
  bool shouldRebuild(SliverHeaderDelegate old) {
    return old.maxExtent != maxExtent || old.minExtent != minExtent;
  }
}