RefreshIndicator

下拉刷新请使用：RefreshIndicator,挺简单，把内容放到child：属性，onRefresh:()async{await}这个无名函数是刷新的具体操作，是一个Future类型的函数。
一个具体的示例：
import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: HomePage(),
    );
  }
}

class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('RefreshIndicator'),),
      body: RefreshIndicator(
        onRefresh: ()async{
          await Future.delayed(Duration(seconds: 5));
        },
        child: ListView(
          children: <Widget>[
            Image.network('http://www.ecobentech.com/images/1.jpg',fit: BoxFit.cover,),
            Image.network('http://www.ecobentech.com/images/2.jpg',fit: BoxFit.cover,),
            Image.network('http://www.ecobentech.com/images/3.jpg',fit: BoxFit.cover,),
            Image.network('http://www.ecobentech.com/images/4.jpg',fit: BoxFit.cover,),
          ],
        ),
      ),
    );
  }
}