Flutter ListView 下拉刷新上拉加载更多

在Flutter中系统已经为我们提供了google material design的刷新功能 , 样式与原生Android一样.
我们可以使用RefreshIndicator组件来实现Flutter中的下拉刷新
使用方法：

import 'package:flutter/material.dart';

class PullToRefreshListViewPage extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return PullToRefreshListViewPageState();
  }
}

class PullToRefreshListViewPageState extends State<PullToRefreshListViewPage> {
  List<String> _dataSoure = new List();
  ScrollController _scrollController;
  int pageNum = 1;
  bool isLoading = false; // 是否正在加载更多
  @override
  void initState() {
    // TODO: implement onCreate
    super.initState();
    _dataSoure = List.generate(8, (i) => '初始数据${i + 1}');
    _scrollController = ScrollController();
    // 监听是否滚动到底部
    _scrollController.addListener(() {
      if (_scrollController.position.pixels >=
              _scrollController.position.maxScrollExtent &&
          pageNum < 5) {
        // 滑动到了底部 执行上拉加载逻辑
        _loadMore();
      }
    });
  }

  @override
  void dispose() {
    // TODO: implement dispose
    super.dispose();
    _scrollController.dispose();
  }

  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return Container(
      color: Color(0xfff5f5f5),
      child: Column(
        children: <Widget>[
          Container(
            margin: EdgeInsets.only(top: 35, bottom: 10),
            child: Text(
              '下拉刷新上拉更多',
              style: TextStyle(
                  fontSize: 17,
                  color: Color(0xff3c3c3c),
                  decoration: TextDecoration.none),
            ),
          ),
          Expanded(
            child: RefreshIndicator(
              child: MediaQuery.removePadding(
                  removeTop: true,
                  context: context,
                  child: ListView.builder(
                      itemCount: _dataSoure.length + 1,
                      controller: _scrollController,
                      itemBuilder: (context, index) {
                        if (index < _dataSoure.length) {
                          return _itemWidget(index);
                        } else {
                          // 最后一项，显示加载更多布局
                          return _loadMoreItem(pageNum < 5 ? '加载中...' : '到底啦');
                        }
                      })),
              onRefresh: _refresh,
            ),
          )
        ],
      ),
    );
  }

  Widget _itemWidget(int index) {
    return Container(
      margin: EdgeInsets.only(bottom: 6),
      padding: EdgeInsets.only(top: 8, left: 16, right: 16, bottom: 8),
      color: Color(0xffffffff),
      child: Row(
        children: <Widget>[
          Container(
            alignment: Alignment.center,
            width: 64,
            height: 64,
            child: ClipRRect(
              borderRadius: BorderRadius.circular(4.0),
              child: new FadeInImage.assetNetwork(
                placeholder: 'assets/defaultImage.png',
                image:
                    'https://wx1.sinaimg.cn/mw690/005uGqDJgy1gfc41hvjxlj323p23pkjl.jpg',
                width: 64,
                height: 64,
                fit: BoxFit.cover,
              ),
            ),
          ),
          Expanded(
              child: Container(
            margin: EdgeInsets.all(10),
            child: Text(
              _dataSoure[index],
              style: TextStyle(
                  fontWeight: FontWeight.normal,
                  fontSize: 16,
                  color: Color(0xff808080),
                  decoration: TextDecoration.none),
            ),
          ))
        ],
      ),
    );
  }

  /// 加载更多Item
  Widget _loadMoreItem(String fontContent) {
    return Center(
      child: Padding(
        padding: EdgeInsets.all(15.0),
        child: Text(fontContent,
            style: TextStyle(
                fontSize: 16,
                fontWeight: FontWeight.normal,
                color: Color(0xff808080),
                decoration: TextDecoration.none)),
      ),
    );
  }

  /// 下拉刷新
  Future<Null> _refresh() async {
    // 延迟加载
    await Future.delayed(Duration(seconds: 2), () {
      setState(() {
        List<String> _refreshData = List.generate(8, (i) => '下拉添加数据${i + 1}');
        pageNum = 1;
        _dataSoure.clear();
        _dataSoure.addAll(_refreshData);
      });
    });
  }

  /// 上拉加载
  Future<Null> _loadMore() async {
    if (!isLoading) {
      setState(() {
        isLoading = true;
      });
      await Future.delayed(Duration(seconds: 2), () {
        setState(() {
          isLoading = false;
          pageNum++;
          List<String> _loadMoreData =
              List.generate(5, (i) => '上拉添加数据${i + 1}');
          _dataSoure.addAll(_loadMoreData);
        });
      });
    }
  }
}