计数器应用程序之外的简单Riverpod示例:两个单元格的总和

Question

我正在学习Flutter，我一直在学习状态管理。我看了一眼Riverpod，它看起来很有前景，但我很难超越计数器应用程序，去做更复杂的事情。

例如，我希望有两个收集数字的TextField，以及另一个显示两个TextField值之和的Text小部件。这是我的东西。

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:hooks_riverpod/hooks_riverpod.dart';
import 'package:flutter_hooks/flutter_hooks.dart';
void main() {
runApp(ProviderScope(
child: MyApp(),
));
}
class MyApp extends HookWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
home: MyHomePage(title: 'Adding two cells'),
);
}
}
final cellProvider = StateProvider((_) => <int>[0, 0]);
class MyHomePage extends HookWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(title),
),
body: Consumer(builder: (context, watch, _) {
print(watch(cellProvider).state);
num _sum = watch(cellProvider).state[0] + watch(cellProvider).state[1];
return Center(
child: Column(
children: [
Row(
mainAxisAlignment: MainAxisAlignment.center,
children: [
Cell(0),
Cell(1),
],
),
SizedBox(
height: 100,
),
Row(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text('Sum: ${_sum.toString()}'),
],
),
],
),
);
}),
);
}
}
class Cell extends HookWidget {
Cell(this.index);
final int index;
@override
Widget build(BuildContext context) {
return Container(
width: 150,
padding: EdgeInsets.all(30),
child: TextField(
inputFormatters: [FilteringTextInputFormatter.digitsOnly],
onChanged: (value) {
context.read(cellProvider).state[index] = num.tryParse(value);
},
),
);
}
}

文本小部件不会更新。有什么建议吗？

非常感谢，Tony

Answer 1

提供者只有在它提供的对象发生更改时才会更新，就像Stream返回更新整个对象(List<int>(所需的最终值一样，这样消费者才能正确更新，更改迭代的内部值不会触发更新

onChanged: (value) {
final List<int> myList = context.read(cellProvider).state;
myList[index] = num.tryParse(value); 
context.read(cellProvider).state = myList; //update the state with a new list
},