【重要】高级功能列表下拉刷新与上拉加载更多功能实现-文档和源码

Question

如何实现列表下拉刷新？

在Flutter中有一个RefreshIndicator，它是一个下拉刷新的widget，通过它我们可以实现列表的下拉刷新。

import 'package:flutter/material.dart';

void main() => runApp(MyApp());
List<String> cityNames = [ '北京', '上海', '广州', '深圳', '杭州', '苏州', '成都', '武汉', '郑州', '洛阳', '厦门', '青岛', '拉萨' ];

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  @override
  Widget build(BuildContext context) {
    final title = '高级功能列表下拉刷新与上拉加载更多功能实现';

    return MaterialApp(
      title: title,
      home: Scaffold(
        appBar: AppBar(
          title: Text(title),
        ),
        body: RefreshIndicator(
          onRefresh: _handleRefresh,
          child: ListView(
            children: _buildList(),
          ),
        ),
      ),
    );
  }

  Future<Null> _handleRefresh() async {
    await Future.delayed(Duration(seconds: 2));
    setState(() {
      cityNames = cityNames.reversed.toList();
    });
    return null;
  }

  List<Widget> _buildList() {
    return cityNames.map((city) => _item(city)).toList();
  }

  Widget _item(String city) {
    return Container(
      height: 80,
      margin: EdgeInsets.only(bottom: 5),
      alignment: Alignment.center,
      decoration: BoxDecoration(color: Colors.teal),
      child: Text(
        city,
        style: TextStyle(color: Colors.white, fontSize: 20),
      ),
    );
  }
}

如何实现上拉加载更多？

为了给列表添加上了加载更多的功能，我们可以借助ScrollController，列表支持设置controller参数，通过ScrollController监听列表滚动的位置，来实现加载更多的功能。

import 'package:flutter/material.dart';

void main() => runApp(MyApp());
List<String> cityNames = [ '北京', '上海', '广州', '深圳', '杭州', '苏州', '成都', '武汉', '郑州', '洛阳', '厦门', '青岛', '拉萨' ];

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  ScrollController _scrollController = ScrollController();

  @override
  void initState() {
    _scrollController.addListener(() {
      if (_scrollController.position.pixels ==
          _scrollController.position.maxScrollExtent) {
        _loadData();
      }
    });

    super.initState();
  }

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

  @override
  Widget build(BuildContext context) {
    final title = '高级功能列表下拉刷新与上拉加载更多功能实现';

    return MaterialApp(
      title: title,
      home: Scaffold(
        appBar: AppBar(
          title: Text(title),
        ),
        body: RefreshIndicator(
          onRefresh: _handleRefresh,
          child: ListView(
            controller: _scrollController,
            children: _buildList(),
          ),
        ),
      ),
    );
  }

  _loadData() async {
    await Future.delayed(Duration(milliseconds: 200));
    setState(() {
      List<String> list = List<String>.from(cityNames);
      list.addAll(cityNames);
      cityNames = list;
    });
  }

  Future<Null> _handleRefresh() async {
    await Future.delayed(Duration(seconds: 2));
    setState(() {
      cityNames = cityNames.reversed.toList();
    });
    return null;
  }

  List<Widget> _buildList() {
    return cityNames.map((city) => _item(city)).toList();
  }

  Widget _item(String city) {
    return Container(
      height: 80,
      margin: EdgeInsets.only(bottom: 5),
      alignment: Alignment.center,
      decoration: BoxDecoration(color: Colors.teal),
      child: Text(
        city,
        style: TextStyle(color: Colors.white, fontSize: 20),
      ),
    );
  }
}

Answer 1

提问者 CrazyCodeBoy 2019-08-01 19:56:13

以上。