传递状态的更好方法，而不是在颤振中创建两条相同的行

Question

所以我正在从 flutter 的网站做教程，然后我修改教程的代码以在有状态小部件上添加删除功能。我认为这是多余的事情(评论 1 到 5(：

import 'package:flutter/material.dart';
import 'package:english_words/english_words.dart';
void main() {
runApp(new MyApp());
}
class SavedWords extends StatefulWidget {
final Set<WordPair> _saved; // 1
SavedWords(this._saved); // 2
@override
createState() => SavedWordState(_saved); // 3
}
class SavedWordState extends State<SavedWords> {
Set<WordPair> _saved; // 4
SavedWordState(this._saved); // 5
@override
Widget build(BuildContext context) {
final tiles = _saved.map(
(pair) {
return new ListTile(
title: new Text(
pair.asPascalCase,
),
trailing: new Icon(Icons.delete),
onTap: () {
setState(() {
_saved.remove(pair);
});
},
);
},
);
final divided = ListTile
.divideTiles(
context: context,
tiles: tiles,
)
.toList();
return new Scaffold(
appBar: new AppBar(
title: new Text('Saved Suggestions'),
),
body: new ListView(children: divided),
);
}
}
class RandomWords extends StatefulWidget {
@override
createState() => RandomWordsState();
}
class RandomWordsState extends State<RandomWords> {
final _suggestions = <WordPair>[];
final _saved = new Set<WordPair>();
final _biggerFont = const TextStyle(fontSize: 18.0);
@override
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(
title: new Text('Startup Name Generator'),
actions: <Widget>[
new IconButton(icon: new Icon(Icons.list), onPressed: _pushSaved),
],
),
body: _buildSuggestions(),
);
}
void _pushSaved() {
Navigator.of(context).push(
new MaterialPageRoute(
builder: (context) {
return new SavedWords(_saved);
},
),
);
}
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,
),
onTap: () {
setState(() {
if (alreadySaved) {
_saved.remove(pair);
} else {
_saved.add(pair);
}
});
},
);
}
}
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return new MaterialApp(
title: 'Startup Name Generator',
home: new RandomWords(),
theme: new ThemeData(
primaryColor: Colors.black,
secondaryHeaderColor: Colors.black,
),
);
}
}

这只是 1 个视图，想象一下，如果有很多视图，有没有更好的方法可以做到这一点？

Answer 1

State<T>子类上不应该有自定义构造函数。

所以你不能做

class SavedWordState extends State<SavedWords> {
Set<WordPair> _saved; // 4
SavedWordState(this._saved); // 5

和

@override
createState() => SavedWordState(_saved); // 3

相反，State<T>有一个T widget属性，用于从StatefulWidget子类中获取字段。

因此，在您的State<T>中，您可以执行以下操作：

class SavedWords extends StatefulWidget {
final Set<WordPair> saved;
SavedWords({ this.saved });
@override
createState() => SavedWordState();
}
...
@override
Widget build(BuildContext context) {
final tiles = widget.saved.map(