• 下拉刷新RefreshIndicator，列表ListView，这里不做过多介绍
• FutureBuilder:Flutter应用中的异步模型，基于与Future交互的最新快照来构建自身的widget 官方文档：docs.flutter.io/flutter/wid…

const FutureBuilder({
Key key,
this.future,//获取数据的方法
this.initialData,
@required this.builder//根据快照的状态，返回不同的widget
}) : assert(builder != null),
super(key: key);

future就是一个定义的异步操作，注意要带上泛型，不然后面拿去snapshot.data的时候结果是dynamic的 snapshot就是future这个异步操作的状态快照，根据它的connectionState去加载不同的widget 有四种快照的状态：

enum ConnectionState {
//future还未执行的快照状态
none,
//连接到一个异步操作，并且等待交互，一般在这种状态的时候，我们可以加载个菊花
waiting,
//连接到一个活跃的操作，比如stream流，会不断地返回值，并还没有结束，一般也是可以加载个菊花
active,
//异步操作执行结束，一般在这里可以去拿取异步操作执行的结果，并显示相应的布局
done,
}

下面的官方的例子。

FutureBuilder(
future: _calculation, // a previously-obtained Future or null
builder: (BuildContext context, AsyncSnapshot snapshot) {
switch (snapshot.connectionState) {
case ConnectionState.none:
return Text(‘Press button to start.’);
case ConnectionState.active:
case ConnectionState.waiting:
return Text(‘Awaiting result…’);
case ConnectionState.done:
if (snapshot.hasError)
return Text(‘Error: ${snapshot.error}’);
return Text(‘Result: ${snapshot.data}’);
}
return null; // unreachable
},
)

3.实现思路，布局方式

• 网络请求：利用Dio库来请求玩Android的知识体系列表，api:www.wanandroid.com/tree/json

• 序列化json：利用json_serializable来解析返回的json数据

• 布局：加载过程显示CircularProgressIndicator，加载完成把数据显示到ListView中， 加载为空或者加载出错的话，显示相应的提示页面，并可以进行重试请求 一般。我们的列表页面都是有下拉刷新的功能，所以这里就用RefreshIndicator来实现。

4.代码实现

import ‘package:flutter/material.dart’;
import ‘package:dio/dio.dart’;
import ‘entity.dart’;

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
// This widget is the root of your application.
@override
Widget build(BuildContext context) {
return MaterialApp(
title: ‘Flutter Demo’,
theme: 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 simply save your changes to “hot reload” in a Flutter IDE).
// Notice that the counter didn’t reset back to zero; the application
// is not restarted.
primarySwatch: Colors.blue,
),
home: FutureBuilderPage(),
);
}
}

class Fu
tureBuilderPage extends StatefulWidget {
@override
_FutureBuilderPageState createState() => _FutureBuilderPageState();
}

class _FutureBuilderPageState extends State {
Future future;

@override
void initState() {
// TODO: implement initState
super.initState();
future = getdata();
}

@override
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(
title: new Text(“知识体系”),
actions: [
new IconButton(
icon: Icon(
Icons.search,
color: Colors.white,
),
onPressed: null)
],
),
body: buildFutureBuilder(),
floatingActionButton: new FloatingActionButton(onPressed: () {
setState(() {
//测试futurebuilder是否进行没必要的重绘操作
});
}),
);
}

FutureBuilder<List> buildFutureBuilder() {
onPressed: () {
setState(() {
//测试futurebuilder是否进行没必要的重绘操作
});
}),
);
}

FutureBuilder<List> buildFutureBuilder() {