Hide Appbar on Scroll Flutter?

问题:

Consider this image. As you can see it has an appbar and the appbar has Tabbed buttons. Am trying to animate the appbar so that it hides on scrollup and leaves only the Tab Buttons showing and on scrollup the appbar apears. Please help me out. Sorry for bad english and not American neither am I English

回答1:

If I understood you correctly, following code should make the app bar hide on scroll while TabBar remains visible:

new Scaffold(
  body: new NestedScrollView(
    controller: _scrollViewController,
    headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
      return <Widget>[
        new SliverAppBar(
          title: new Text(widget.title),
          pinned: true,
          floating: true,
          forceElevated: innerBoxIsScrolled,
          bottom: new TabBar(
            tabs: <Tab>[
              new Tab(text: "STATISTICS"),
              new Tab(text: "HISTORY"),
            ],
            controller: _tabController,
          ),
        ),
      ];
    },
    body: new TabBarView(
      children: <Widget>[
        new StatisticsPage(),
        new HistoryPage(),
      ],
      controller: _tabController,
    ),
  ),
);

Example coming from this post.

回答2:

I suggest that you have to go through SliverAppBar and SliverList To achieve your layout. Following code may help you to understand that.

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Demo',
      home: new MyHomePage(),
      debugShowCheckedModeBanner: false,
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {

    List buildTextViews(int count) {
      List<Widget> strings = List();
      for (int i = 0; i < count; i++) {
        strings.add(new Padding(padding: new EdgeInsets.all(16.0),
            child: new Text("Item number " + i.toString(),
                style: new TextStyle(fontSize: 20.0))));
      }
      return strings;
    }

    return Scaffold(
        body: new CustomScrollView(slivers: <Widget>[
          const SliverAppBar(
            title: const Text('Sliver App Bar'),
          ),
          new SliverList(
              delegate: new SliverChildListDelegate(buildTextViews(50)))
        ])
    );
  }
}

回答3:

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(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage>
    with SingleTickerProviderStateMixin {
  bool _showAppbar = true;
  ScrollController _scrollBottomBarController = new ScrollController();
  bool isScrollingDown = false;
  bool _show = true;
  double bottomBarHeight = 75;
  double _bottomBarOffset = 0;

  @override
  void initState() {
    super.initState();
    myScroll();    
  }

  @override
  void dispose() {
    super.dispose();
    _scrollBottomBarController.removeListener(() {});
    super.dispose();
  }

  void showBottomBar() {
    setState(() {
      _show = true;
    });
  }

  void hideBottomBar() {
    setState(() {
      _show = false;
    });
  }

  void myScroll() async {
    _scrollBottomBarController.addListener(() {
      if (_scrollBottomBarController.position.userScrollDirection ==
          ScrollDirection.reverse) {
        if (!isScrollingDown) {
          isScrollingDown = true;
          _showAppbar = false;
          hideBottomBar();
        }
      }
      if (_scrollBottomBarController.position.userScrollDirection ==
          ScrollDirection.forward) {
        if (isScrollingDown) {
          isScrollingDown = false;
          _showAppbar = true;
          showBottomBar();
        }
      }
    });
  }

  Widget containterContent(){
    return Container(
      height: 50.0,
      color: Colors.cyanAccent,
      margin: EdgeInsets.all(8.0),
      width: MediaQuery.of(context).size.width - 100,
      child: Center(child: Text('Item 1',
        style: TextStyle(
          fontSize: 14.0,
        ),)),
    );
  }

  Widget body() {
    return ListView(
      controller: _scrollBottomBarController,
      children: <Widget>[
        containterContent(),
        containterContent(),
        containterContent(),
        containterContent(),
        containterContent(),
        containterContent(),
        containterContent(),
        containterContent(),
        containterContent(),
        containterContent(),

      ],
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: _showAppbar
          ? AppBar(
        title: Text('My Tasks'),
      )
          : PreferredSize(
        child: Container(),
        preferredSize: Size(0.0, 0.0),
      ),
      bottomNavigationBar: Container(
        height: bottomBarHeight,
        width: MediaQuery.of(context).size.width,
        child: _show
            ?BottomNavigationBar(
          currentIndex: 0, // this will be set when a new tab is tapped
          items: [
            BottomNavigationBarItem(
              icon: new Icon(Icons.home),
              title: new Text('Home'),
            ),
            BottomNavigationBarItem(
              icon: new Icon(Icons.mail),
              title: new Text('Messages'),
            ),
            BottomNavigationBarItem(
                icon: Icon(Icons.person), title: Text('Profile'))
          ],
        )
            : Container(
          color: Colors.white,
          width: MediaQuery.of(context).size.width,
        ),
      ),

      body: body(
      ),

    );
  }
}