更新状态时如何避免重复查找状态？

Question

这里我有颤振提供者的代码

class Page extends StatelessWidget {
  GlobalState? _state;
  GlobalState get state => _state!;
  set state(GlobalState value) => _state ??= value;

  Widget build(BuildContext context) {
      state = context.read<GlobalState>();
      return Selector<GlobalState, int> (
         selector: (_, innerState) => innerState.intValue,
         builder: (_, value, child) => ...
      );
   }
}

我确信状态会在第一次构建时被初始化，下次程序会发现状态不为空并且不会协助

context.read<GlobalState>

， 但是在

Selector

中，每次当状态

notifyListener

时，

Selector

总是会再次寻找相同的

GlobalState

，我该如何改进我的代码？

我想我已经找到了

GlobalState

所在的位置，所以不需要再寻找

GlobalState

，我不知道如何在

Provider

中修复它，或者我应该转向

getx 

？

Answer 1

这是在您的案例中使用

ChangeNotifier

的示例。可以分割小Widget直接返回

Selector

.

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';

void main() {
  runApp(
    MultiProvider(
      providers: [
        ChangeNotifierProvider(create: (_) => Counter()),
      ],
      child: const MyApp(),
    ),
  );
}

class Counter with ChangeNotifier {
  int _count = 0;

  int get count => _count;

  void increment() {
    _count++;
    notifyListeners();
  }
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatelessWidget {
  const MyHomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Example'),
      ),
      body: Center(
        child: Selector<Counter, int>(
          builder: (context, data, child) {
            return Container(
              height: 40,
              color: Colors.red,
              child: Center(child: Text('Consumer1: $data')),
            );
          },
          selector: (buildContext, state) {
            return state.count;
          },
        ),
      ),
      floatingActionButton: FloatingActionButton(
        key: const Key('increment_floatingActionButton'),

        /// Calls `context.read` instead of `context.watch` so that it does not rebuild
        /// when [Counter] changes.
        onPressed: () => context.read<Counter>().increment(),
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ),
    );
  }
}