小编nes*_*scx的帖子

当用户在屏幕上滚动时，我想从SliverAppBar中“淡入”和“淡出”小部件。

这是我想做的一个例子：

这是我的代码，没有“褪色”：

https://gist.github.com/nesscx/721cd823350848e3d594ba95df68a7fa

导入'package：flutter / material.dart';

class App extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Fading out CircleAvatar',
      theme: ThemeData(
        primarySwatch: Colors.purple,
      ),
      home: Scaffold(
        body: DefaultTabController(
          length: 2,
          child: NestedScrollView(
            headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
              return <Widget>[
                SliverOverlapAbsorber(
                  handle: NestedScrollView.sliverOverlapAbsorberHandleFor(context),
                  child: new SliverAppBar(
                    expandedHeight: 254.0,
                    pinned: false,
                    leading: Icon(Icons.arrow_back),
                    title:Text('Fade'),
                    forceElevated: innerBoxIsScrolled, 
                    flexibleSpace: new FlexibleSpaceBar(
                      centerTitle: true,
                      title: Column(
                        mainAxisAlignment: MainAxisAlignment.end,
                        children: <Widget>[
                          CircleAvatar(
                            radius: 36.0,
                            child: Text(
                              'N',
                              style: TextStyle(
                                color: Colors.white, …