滚动列表

示例: 无限滚动列表

import 'package:flutter/material.dart';
import 'package:english_words/english_words.dart';
void main() {
  runApp(new MyApp());
}
class MyApp extends StatelessWidget {
  
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Demo',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new RandomWords(),
    );
  }
}
class RandomWords extends StatefulWidget {
  
  createState() => new RandomWordsState();
}
class RandomWordsState extends State<RandomWords> {
  final _suggestions = <WordPair>[];
  final _biggerFont = const TextStyle(fontSize: 20.0);
  
  Widget build(BuildContext context) {
    return new Scaffold (
      appBar: new AppBar(
        title: new Text('无限滚动列表'),
      ),
      body: _buildSuggestions(),
    );
  }
  Widget _buildSuggestions() {
    return new ListView.builder(
      padding: const EdgeInsets.all(16.0),
      // 对于每个建议的单词对都会调用一次itemBuilder,然后将单词对添加到ListTile行中
      // 在偶数行,该函数会为单词对添加一个ListTile row.
      // 在奇数行,该函数会添加一个分割线widget,来分隔相邻的词对。
      itemBuilder: (context, i) {
        // 在每一列之前,添加一个1像素高的分隔线widget
        if (i.isOdd) return new Divider();
        // 语法 "i ~/ 2" 表示i除以2,但返回值是整形(向下取整),比如i为:1, 2, 3, 4, 5 时,结果为0, 1, 1, 2, 2, 这可以计算出ListView中减去分隔线后的实际单词对数量
        final index = i ~/ 2;
        // 如果是建议列表中最后一个单词对
        if (index >= _suggestions.length) {
          // ...接着再生成10个单词对,然后添加到建议列表
          _suggestions.addAll(generateWordPairs().take(10));
        }
        return _buildRow(_suggestions[index]);
      }
    );
  }
  Widget _buildRow(WordPair pair) {
    return new ListTile(
      title: new Text(
        pair.asPascalCase,
        style: _biggerFont,
      ),
    );
  }
}

示例: ListView 的点击事件处理, 并记住选中状态

class RandomWordsState extends State<RandomWords> {
  final _suggestions = <WordPair>[];
  final _saved = new Set<WordPair>();
  final _biggerFont = const TextStyle(fontSize: 20.0);
  
  Widget build(BuildContext context) {
    return new Scaffold (
      appBar: new AppBar(
        title: new Text('无限滚动列表'),
      ),
      body: _buildSuggestions(),
    );
  }
  Widget _buildSuggestions() {
    return new ListView.builder(
      padding: const EdgeInsets.all(16.0),
      itemBuilder: (context, i) {
        if (i.isOdd) return new Divider();
        final index = i ~/ 2;
        if (index >= _suggestions.length) {
          _suggestions.addAll(generateWordPairs().take(10));
        }
        return _buildRow(_suggestions[index]);
      }
    );
  }
  Widget _buildRow(WordPair pair) {
    final alreadySaved = _saved.contains(pair);
    return new ListTile(
      title: new Text(
        pair.asPascalCase,
        style: _biggerFont,
      ),
      trailing: new Icon(
        alreadySaved ? Icons.favorite : Icons.favorite_border,
        color: alreadySaved ? Colors.red : null,
      ),
      // 处理点击事件
      onTap: () {
        setState(() {
          if (alreadySaved) {
            _saved.remove(pair);
          } else {
            _saved.add(pair);
          }
        });
      },
    );
  }
}

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