Flutter-刷新和加载更多控件

import 'dart:math';

import 'package:flutter/material.dart';

void main() => runApp(MaterialApp(
      home: HomePage(),
    ));

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

class _HomePageState extends State {
  List list = List();
  ScrollController _scrollController;

  @override
  void initState() {
    super.initState();
    _refresh();
    _scrollController = ScrollController()
      ..addListener(() {
        //判断是否滑到底
        if (_scrollController.position.pixels ==
            _scrollController.position.maxScrollExtent) {
          _loadMore();
        }
      });
  }

  @override
  void dispose() {
    super.dispose();
    _scrollController.dispose();
  }

  Future _loadMore() async {
    await Future.delayed(Duration(seconds: 2), () {
      setState(() {
        list.addAll(
            List.generate(Random().nextInt(5) + 1, (i) => 'more Item $i'));
      });
    });
  }

  Future _refresh() async {
    await Future.delayed(Duration(seconds: 3), () {
      setState(() {
        list = List.generate(Random().nextInt(20) + 15, (i) => 'Item $i');
      });
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('下拉刷新'),
      ),
      body: Center(
        child: RefreshIndicator(
            displacement: 10.0,
            child: list == null || list.isEmpty
                ? Center(
                    child: CircularProgressIndicator(),
                  )
                : ListView.builder(
                    controller: _scrollController,
                    itemCount: list.length + 1,
                    itemBuilder: (context, index) {
                      if(index == list.length){
                        return Padding(
                          padding: const EdgeInsets.all(10.0),
                          child: Center(
                            child: CircularProgressIndicator(),
                          ),
                        );
                      }
                      return ListTile(
                        title: Text(list[index]),
                      );
                    }),
            onRefresh: _refresh),
      ),
    );
  }
}