ensureVisible 演示

ensureVisible.dart

import 'package:flutter/material.dart';

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

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key key}) : super(key: key);

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  ScrollController _scrollController = ScrollController();
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(),
      body: CustomScrollView(
        controller: _scrollController,
        slivers: <Widget>[
          SliverToBoxAdapter(
            child: Container(
              height: 150,
              color: Colors.red,
            ),
          ),
          SliverList(
            delegate: SliverChildBuilderDelegate(
              (BuildContext b, int index) {
                return Container(
                  height: 50,
                  alignment: Alignment.center,
                  child: Text('$index'),
                );
              },
              childCount: 3,
            ),
          ),
          SliverToBoxAdapter(
            child: Builder(
              builder: (BuildContext context) {
                return RaisedButton(
                  onPressed: () {
                    _scrollController.position.ensureVisible(
                      context.findRenderObject(),
                      duration: Duration(
                        seconds: 1,
                      ),
                    );
                  },
                  child: Text('点我跳转顶部'),
                );
              },
            ),
          ),
          SliverPersistentHeader(
            delegate: MySliverPersistentHeaderDelegate(_scrollController),
            pinned: true,
          ),
          SliverList(
            delegate: SliverChildBuilderDelegate(
              (BuildContext b, int index) {
                return Container(
                  height: 100,
                  alignment: Alignment.center,
                  child: Text('$index'),
                );
              },
              childCount: 100,
            ),
          )
        ],
      ),
    );
  }
}

class MySliverPersistentHeaderDelegate extends SliverPersistentHeaderDelegate {
  MySliverPersistentHeaderDelegate(this.scrollController);
  final ScrollController scrollController;

  @override
  Widget build(
      BuildContext context, double shrinkOffset, bool overlapsContent) {
    return Builder(
      builder: (BuildContext context) {
        return RaisedButton(
          onPressed: () {
            scrollController.position.ensureVisible(
              context.findRenderObject(),
              duration: Duration(
                seconds: 1,
              ),
            );
          },
          child: Text('点我跳转顶部,我是固定的'),
        );
      },
    );
  }

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

  @override
  double get maxExtent => 48;

  @override
  double get minExtent => 48;
}