SliverAppBar Widget in Flutter

This Article is posted by seven.srikanth at 01-11-2018 05:28:37

In this example, we deal below queries.
How to create a SliverAppBar?
How to add a ListView to SliverAppBar?
How to automatically adjust the text color in SliverAppBar when collapsed?
Here is the final output of this program.
Here is the final code from main.dart. All you need to do is, copy paste this code into your newly created flutter project and run.
import 'package:flutter/material.dart';
void main() => runApp(new MyApp());
class MyApp extends StatelessWidget {
// This widget is the root of your application.
@override
Widget build(BuildContext context) {
return new MaterialApp(
title: 'Flutter Demo',
theme: new ThemeData(
// This is the theme of your application.
//
// Try running your application with "flutter run". You'll see the
// application has a blue toolbar. Then, without quitting the app, try
// changing the primarySwatch below to Colors.green and then invoke
// "hot reload" (press "r" in the console where you ran "flutter run",
// or press Run > Flutter Hot Reload in IntelliJ). Notice that the
// counter didn't reset back to zero; the application is not restarted.
primarySwatch: Colors.blue,
),
home: new MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
// This widget is the home page of your application. It is stateful, meaning
// that it has a State object (defined below) that contains fields that affect
// how it looks.
// This class is the configuration for the state. It holds the values (in this
// case the title) provided by the parent (in this case the App widget) and
// used by the build method of the State. Fields in a Widget subclass are
// always marked "final".
final String title;
@override
_MyHomePageState createState() => new _MyHomePageState();
}
ScrollController _controller;
class _MyHomePageState extends State<MyHomePage> {
@override
void initState() {
_controller = ScrollController();
_controller.addListener(_scrollListener);
super.initState();
}
Color clr = Colors.lightGreen;
_scrollListener() {
if (_controller.offset > _controller.position.minScrollExtent &&
!_controller.position.outOfRange) {
setState(() {
clr = Colors.red;
});
}
if (_controller.offset <= _controller.position.minScrollExtent &&
!_controller.position.outOfRange) {
setState(() {
clr = Colors.lightGreen;
});
}
}
@override
Widget build(BuildContext context) {
// This method is rerun every time setState is called, for instance as done
// by the _incrementCounter method above.
//
// The Flutter framework has been optimized to make rerunning build methods
// fast, so that you can just rebuild anything that needs updating rather
// than having to individually change instances of widgets.
return new Scaffold(
appBar: new AppBar(
// Here we take the value from the MyHomePage object that was created by
// the App.build method, and use it to set our appbar title.
title: new Text("Hello"),
),
body: new Center(
// Center is a layout widget. It takes a single child and positions it
// in the middle of the parent.
child:
new Container(
child:
CustomScrollView(
controller: _controller,
slivers: <Widget>[
SliverAppBar(
pinned: true,
expandedHeight: 250.0,
flexibleSpace: FlexibleSpaceBar(
title: Text("Demo",
style: const TextStyle(
fontSize: 10.0,
fontWeight: FontWeight.w900,
color: Colors.green,
)),
background: FlutterLogo(
size: 20.0,
colors: Colors.blue,
),
),
backgroundColor: clr,
),
SliverFixedExtentList(
itemExtent: 50.0,
delegate: SliverChildBuilderDelegate(
(BuildContext context, int index) {
return Container(
alignment: Alignment.center,
color: Colors.lightBlue[100 * (index % 9)],
child: Text('list item $index'),
);
},
childCount: 50,
),
),
],
),
),
),
);
}
}
Hope this is helpful.
Thanks,
Srikanth

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