flutter下拉刷新上拉加载 简单使用

使用flutter_easyrefresh库
本实例：flutter_easyrefresh版本： ^1.2.7
import ‘dart:async’;

```java
import 'package:flutter/material.dart';
import 'package:flutter_easyrefresh/easy_refresh.dart';
import 'package:flutter_easyrefresh/bezier_circle_header.dart'; //如果要使用炫酷的样式需要引入，不同的样式引入不同的文件，详见官方api
import 'package:flutter_easyrefresh/bezier_bounce_footer.dart'; //如果要使用炫酷的样式需要引入，不同的样式引入不同的文件，详见官方api

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

class MyApp extends StatelessWidget {
     
  @override
  Widget build(BuildContext context) {
     
    return new MaterialApp(
      // App名字
      title: 'EasyRefresh',
      // App主题
      theme: new ThemeData(
        primarySwatch: Colors.orange,
      ),
      // 主页
      home: BasicPage(),
    );
  }
}

class BasicPage extends StatefulWidget {
     
  @override
  _BasicPageState createState() => _BasicPageState();
}

class _BasicPageState extends State<BasicPage> {
     
  List<String> addStr = ["11", "21", "31", "41", "51", "6", "7", "8", "9", "0"];
  List<String> str = ["1", "2", "3", "4", "5", "6", "7", "8", "9", "0"];
  GlobalKey<EasyRefreshState> _easyRefreshKey =
      new GlobalKey<EasyRefreshState>();
  GlobalKey<RefreshHeaderState> _headerKey =
      new GlobalKey<RefreshHeaderState>();
  GlobalKey<RefreshFooterState> _footerKey =
      new GlobalKey<RefreshFooterState>();

  @override
  Widget build(BuildContext context) {
     
    return Scaffold(
      appBar: AppBar(
        title: Text("EasyRefresh"),
      ),
      body: Center(
          child: new EasyRefresh(
        key: _easyRefreshKey,
        refreshHeader: BezierCircleHeader(
          key: _headerKey,
          color: Theme.of(context).scaffoldBackgroundColor,
        ),
        refreshFooter: BezierBounceFooter(
          key: _footerKey,
          color: Theme.of(context).scaffoldBackgroundColor,
        ),
        child: new ListView.builder(
            //ListView的Item
            itemCount: str.length,
            itemBuilder: (BuildContext context, int index) {
     
              return new Container(
                  height: 70.0,
                  child: Card(
                    child: new Center(
                      child: new Text(
                        str[index],
                        style: new TextStyle(fontSize: 18.0),
                      ),
                    ),
                  ));
            }),
        onRefresh: () async {
     
          await new Future.delayed(const Duration(seconds: 1), () {
     
            setState(() {
     
              str.clear();
              str.addAll(addStr);
            });
          });
        },
        loadMore: () async {
     
          await new Future.delayed(const Duration(seconds: 1), () {
     
            if (str.length < 20) {
     
              setState(() {
     
                str.addAll(addStr);
              });
            }
          });
        },
      )),
     // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}