多个ChangeNotifierProxyProviders将更新馈送到ChangeNotifier

发布于 2025-02-04 05:58:35 字数 761 浏览 4 评论 0原文

我有三个changeNotifierProvider提供商，让我们称它们为a，b和c。

我需要的是提供商的更改a和b以更新提供商c，但是下面的代码不起作用。

MultiProvider(
  providers: [
    ChangeNotifierProvider(create: (context) => A()),
    ChangeNotifierProvider(create: (context) => B()),
    ChangeNotifierProxyProvider<A, C>(
      create: (context) => C(),
      update: (_, a, c) => c!..updateFromA(a),
    ),
    ChangeNotifierProxyProvider<B, C>(
      create: (context) => C(),
      update: (_, b, c) => c!..updateFromB(b),
    ),
  ]

我认为它不起作用的原因是因为我最终获得了多个提供商c的副本，但是我不确定如何修复它或更好的替代实现是什么样的。

原文

I have three ChangeNotifierProvider providers, let's call them A, B and C.

What I need is for changes in providers A and B to update provider C, but the code below isn't working.

MultiProvider(
  providers: [
    ChangeNotifierProvider(create: (context) => A()),
    ChangeNotifierProvider(create: (context) => B()),
    ChangeNotifierProxyProvider<A, C>(
      create: (context) => C(),
      update: (_, a, c) => c!..updateFromA(a),
    ),
    ChangeNotifierProxyProvider<B, C>(
      create: (context) => C(),
      update: (_, b, c) => c!..updateFromB(b),
    ),
  ]

I think the reason why it doesn't work is because I end up with multiple copies of provider C, but I am not sure how to fix it or what a better alternative implementation would look like.

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倾城花音 2025-02-11 05:58:35

进行了一些搜索之后，我意识到Flutter提供了一种使用changeNotifierProxyProvider2来解决此问题的优雅开箱即用的方式。

MultiProvider(
  providers: [
    ChangeNotifierProvider(create: (context) => A()),
    ChangeNotifierProvider(create: (context) => B()),
    ChangeNotifierProxyProvider2<A, B, C>(
      create: (context) => C(),
      update: (_, a, b, c) => c!..updateFromA(a)..updateFromB(b),
    ),
  ]

Flutter还提供ChangeNotifierProxyProvider3通过changeNotifierProxyProvider6，但这当然会变得非常冗长且令人困惑。

After doing some searching, I realized that Flutter provides an elegant out-of-the-box way of solving this problem using ChangeNotifierProxyProvider2.

MultiProvider(
  providers: [
    ChangeNotifierProvider(create: (context) => A()),
    ChangeNotifierProvider(create: (context) => B()),
    ChangeNotifierProxyProvider2<A, B, C>(
      create: (context) => C(),
      update: (_, a, b, c) => c!..updateFromA(a)..updateFromB(b),
    ),
  ]

Flutter also provides ChangeNotifierProxyProvider3 through ChangeNotifierProxyProvider6, but that would, of course, get very verbose and confusing.

回复收藏 0 原文

注定孤独终老 2025-02-11 05:58:35

如果问题是一个以上的实例，那么我认为您可以使用提供者。

MultiProvider(
  providers: [
    ChangeNotifierProvider(create: (context) => A()),
    ChangeNotifierProvider(create: (context) => B()),
    ChangeNotifierProvider(create: (context) => C()),
    ChangeNotifierProxyProvider<A, C>(
      create: (context) => Provider.of<C>(context),
      update: (_, a, c) => c!..updateFromA(a),
    ),
    ChangeNotifierProxyProvider<B, C>(
      create: (context) => Provider.of<C>(context),
      update: (_, b, c) => c!..updateFromB(b),
    ),
  ]

否则，您可以将Singleton模式应用于C：

class C {
  static final C _instance = C._();

  factory C() {
    return _instance;
  }

  C._();
}

MultiProvider(
  providers: [
    ChangeNotifierProvider(create: (context) => A()),
    ChangeNotifierProvider(create: (context) => B()),
    ChangeNotifierProxyProvider<A, C>(
      create: (context) => C(),
      update: (_, a, c) => c!..updateFromA(a),
    ),
    ChangeNotifierProxyProvider<B, C>(
      create: (context) => C(),
      update: (_, b, c) => c!..updateFromB(b),
    ),
  ]

If having more than one instance of C is the problem, then I think you can just use Provider.of<C>(context) to get a single instance.

MultiProvider(
  providers: [
    ChangeNotifierProvider(create: (context) => A()),
    ChangeNotifierProvider(create: (context) => B()),
    ChangeNotifierProvider(create: (context) => C()),
    ChangeNotifierProxyProvider<A, C>(
      create: (context) => Provider.of<C>(context),
      update: (_, a, c) => c!..updateFromA(a),
    ),
    ChangeNotifierProxyProvider<B, C>(
      create: (context) => Provider.of<C>(context),
      update: (_, b, c) => c!..updateFromB(b),
    ),
  ]

Or else, you could apply the singleton pattern to C:

class C {
  static final C _instance = C._();

  factory C() {
    return _instance;
  }

  C._();
}

MultiProvider(
  providers: [
    ChangeNotifierProvider(create: (context) => A()),
    ChangeNotifierProvider(create: (context) => B()),
    ChangeNotifierProxyProvider<A, C>(
      create: (context) => C(),
      update: (_, a, c) => c!..updateFromA(a),
    ),
    ChangeNotifierProxyProvider<B, C>(
      create: (context) => C(),
      update: (_, b, c) => c!..updateFromB(b),
    ),
  ]

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