颤音:使用sliver小部件时，如何隐藏滚动底部的底部

Question

当用户向下滚动列表时，我正在尝试隐藏底部的应用程序栏，就像行为部分中的材料设计文档中所示：

https://material.io/design/components/app-bars-bottom.html#behavior

我正在寻找的效果在这里显示：https://storage.googleapis.com/spec-host-backup/mio-design/assets/1gasrddfoldd8bwoioeyz0odiyehcevtn/behavior-scroll.mp4

到目前为止，我在脚手架上添加了底部应用程序栏，但没有滚动的行为。

在Stackoverflow上回答了一个类似的问题，但它显示了一项工作，并且已经回答了一段时间。

是否有合理的方法可以在扑朔迷离中实现这种效果？

我的代码：

import 'package:fitness_fatality_flutter/data/entities/exercise.dart';
import 'package:fitness_fatality_flutter/data/entities/workout.dart';
import 'package:flutter/material.dart';
class WorkoutDetailsPage extends StatelessWidget {
  Workout _workout = Workout();
  final List<Exercise> exercises = [
    Exercise(name: "Push Ups"),
    Exercise(name: "Bench press"),
    Exercise(name: "Pull ups"),
    Exercise(name: "Press ups"),
    Exercise(name: "Crunches"),
    Exercise(name: "Sit ups"),
    Exercise(name: "BIceps curl"),
    Exercise(name: "Something else"),
    Exercise(name: "Push Ups"),
    Exercise(name: "Bench press"),
    Exercise(name: "Pull ups"),
    Exercise(name: "Press ups"),
    Exercise(name: "Crunches"),
    Exercise(name: "Sit ups"),
    Exercise(name: "BIceps curl"),
    Exercise(name: "Something else"),
    Exercise(name: "Push Ups"),
    Exercise(name: "Bench press"),
    Exercise(name: "Pull ups"),
    Exercise(name: "Press ups"),
    Exercise(name: "Crunches"),
    Exercise(name: "Sit ups"),
    Exercise(name: "BIceps curl"),
    Exercise(name: "Something else"),
    Exercise(name: "Push Ups"),
    Exercise(name: "Bench press"),
    Exercise(name: "Pull ups"),
    Exercise(name: "Press ups"),
    Exercise(name: "Crunches"),
    Exercise(name: "Sit ups"),
    Exercise(name: "BIceps curl"),
    Exercise(name: "Something else"),
    Exercise(name: "Push Ups"),
    Exercise(name: "Bench press"),
    Exercise(name: "Pull ups"),
    Exercise(name: "Press ups"),
    Exercise(name: "Crunches"),
    Exercise(name: "Sit ups"),
    Exercise(name: "BIceps curl"),
    Exercise(name: "Something else"),
  ];
  WorkoutDetailsPage(this._workout);
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      floatingActionButtonAnimator: FloatingActionButtonAnimator.scaling,
      floatingActionButtonLocation: FloatingActionButtonLocation.endDocked,
      floatingActionButton: FloatingActionButton(
        backgroundColor: Colors.blue,
        elevation: 12,
        onPressed: () {},
      ),
      bottomNavigationBar: BottomAppBar(
        elevation: 8,
        shape: CircularNotchedRectangle(),
        color: Colors.blue,
        child: Container(
          height: 50,
          child: Row(
            children: <Widget>[Text("data")],
          ),
        ),
      ),
      body: CustomScrollView(
        slivers: <Widget>[
          SliverAppBar(
            bottom:BottomAppBar(), //<-- This would throw an error
            expandedHeight: 150,
            pinned: true,
            floating: true,
            snap: true,
            flexibleSpace: FlexibleSpaceBar(
              title: Text(_workout.name),
            ),
          ),
          SliverList(
            delegate: SliverChildBuilderDelegate(buildSliverListItem,
                childCount: exercises.length),
          ),
        ],
      ),
    );
  }
  Widget buildSliverListItem(BuildContext context, int index) {
    return Center(
      child: ListTile(
        title: Text(exercises[index].name),
      ),
    );
  }
}

Answer 1

BottomAppBar是Scaffold小部件的一部分，而不是Sliver。有一种方法可以实现您所描述的东西，但是有点复杂，需要StatefulWiget和ScrollController，AnimatedContainer。请参阅下面的完整示例代码：

import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: WorkoutDetailsPage(Workout()),
    );
  }
}
class Exercise {
  String name;
  Exercise({@required name}) {
    this.name = name;
  }
}
class Workout {
  String name = "my name";
}
class WorkoutDetailsPage extends StatefulWidget {
  Workout _workout = Workout();
  WorkoutDetailsPage(this._workout);
  @override
  _WorkoutDetailsPageState createState() => _WorkoutDetailsPageState();
}
class _WorkoutDetailsPageState extends State<WorkoutDetailsPage> {
  final List<Exercise> exercises = [
    Exercise(name: "Push Ups"),
    Exercise(name: "Bench press"),
    Exercise(name: "Pull ups"),
    Exercise(name: "Press ups"),
    Exercise(name: "Crunches"),
    Exercise(name: "Sit ups"),
    Exercise(name: "BIceps curl"),
    Exercise(name: "Something else"),
    Exercise(name: "Push Ups"),
    Exercise(name: "Bench press"),
    Exercise(name: "Pull ups"),
    Exercise(name: "Press ups"),
    Exercise(name: "Crunches"),
    Exercise(name: "Sit ups"),
    Exercise(name: "BIceps curl"),
    Exercise(name: "Something else"),
    Exercise(name: "Push Ups"),
    Exercise(name: "Bench press"),
    Exercise(name: "Pull ups"),
    Exercise(name: "Press ups"),
    Exercise(name: "Crunches"),
    Exercise(name: "Sit ups"),
    Exercise(name: "BIceps curl"),
    Exercise(name: "Something else"),
    Exercise(name: "Push Ups"),
    Exercise(name: "Bench press"),
    Exercise(name: "Pull ups"),
    Exercise(name: "Press ups"),
    Exercise(name: "Crunches"),
    Exercise(name: "Sit ups"),
    Exercise(name: "BIceps curl"),
    Exercise(name: "Something else"),
    Exercise(name: "Push Ups"),
    Exercise(name: "Bench press"),
    Exercise(name: "Pull ups"),
    Exercise(name: "Press ups"),
    Exercise(name: "Crunches"),
    Exercise(name: "Sit ups"),
    Exercise(name: "BIceps curl"),
    Exercise(name: "Something else"),
  ];
  ScrollController _hideButtonController;
  bool _isVisible = true;
  @override
  void initState() {
    super.initState();
    _isVisible = true;
    _hideButtonController = new ScrollController();
    _hideButtonController.addListener(() {
      print("listener");
      if (_hideButtonController.position.userScrollDirection ==
          ScrollDirection.reverse) {
        setState(() {
          _isVisible = false;
          print("**** $_isVisible up");
        });
      }
      if (_hideButtonController.position.userScrollDirection ==
          ScrollDirection.forward) {
        setState(() {
          _isVisible = true;
          print("**** $_isVisible down");
        });
      }
    });
  }
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      floatingActionButtonAnimator: FloatingActionButtonAnimator.scaling,
      floatingActionButtonLocation: FloatingActionButtonLocation.centerDocked,
      floatingActionButton: _isVisible
          ? FloatingActionButton(
              backgroundColor: Colors.blue,
              elevation: 12,
              onPressed: () {},
            )
          : null,
      bottomNavigationBar: AnimatedContainer(
        duration: Duration(milliseconds: 200),
        height: _isVisible ? 60 : 0.0,
        child: BottomAppBar(
          elevation: 8,
          shape: CircularNotchedRectangle(),
          color: Colors.blue,
          child: Container(
            height: 60,
            child: Row(
              children: <Widget>[Text("data")],
            ),
          ),
        ),
      ),
      body: CustomScrollView(
        controller: _hideButtonController,
        slivers: <Widget>[
          SliverAppBar(
            expandedHeight: 150,
            pinned: true,
            floating: true,
            snap: true,
            flexibleSpace: FlexibleSpaceBar(
              title: Text(widget._workout.name),
            ),
          ),
          SliverList(
            delegate: SliverChildBuilderDelegate(buildSliverListItem,
                childCount: exercises.length),
          ),
        ],
      ),
    );
  }
  Widget buildSliverListItem(BuildContext context, int index) {
    return Center(
      child: ListTile(
        title: Text(exercises[index].name),
      ),
    );
  }
}