Flutter - MultiProvider 如何与相同类型的提供者一起工作? [英] Flutter - How does MultiProvider work with providers of the same type?

问题描述

例如，我试图一次获取为多个流发出的数据，但是这些流中有 2 个或更多发出相同类型的数据，比如说一个字符串.

For example, I am trying to obtain data emitted for multiple streams at once, but 2 or more of these streams emit data of the same type, lets say a string.

我的问题是，是否可以同时使用相同类型的 MultiProvider 和多个 StreamProvider(或任何提供者，但我对这种情况感兴趣)能够访问每个人发出的数据吗?

My question is, is it possible to use MultiProvider and use multiple StreamProvider (or any provider, but I am interested in this case) of the same type while still being able to access the data emitted by each one of them?

一个解决方案是在使用常见数据类型时使用 StreamBuilder，但我真的很喜欢 MultiProvider 在更简洁的代码方面提供的功能.

A solution for this is using a StreamBuilder when using common data types but I really like what the MultiProvider offers in terms of cleaner code.

示例:

class MyScreen extends StatelessWidget {
  Widget build(BuildContext context) {
    return MultiProvider(
      providers: [
        StreamProvider<String>(stream: Observable.just("stream1")),
        StreamProvider<String>(stream: Observable.just("stream2")),
        StreamProvider<String>(stream: Observable.just("stream3"))
      ],
      child: Builder(
        builder: (BuildContext context) {
          AsyncSnapshot<String> snapshot =
              Provider.of<AsyncSnapshot<String>>(context);
          String data = snapshot.data;
          return Text(data); 
        },
      ),
    );
  }
}

推荐答案

MultiProvider 与否不会改变任何事情.如果两个提供程序共享相同的类型，则最深的一个覆盖该值.

MultiProvider or not doesn't change anything. If two providers share the same type, the deepest one overrides the value.

不可能从不是给定类型最接近祖先的提供者那里获取值.

It's not possible to obtain the value from a provider that is not the closest ancestor for a given type.

如果您需要独立访问所有这些值，每个值都应该有一个唯一的类型.

If you need to access all of these values independently, each should have a unique type.

例如，代替:

Provider<int>(
  value: 42,
  child: Provider<int>(
    value: 84,
    child: <something>
  ),
)

你可以这样做:

class Root {
  Root(this.value);

  final int value;
}

class Leaf {
  Leaf(this.value);

  final int value;
}


Provider<Root>(
  value: Root(42),
  child: Provider<Leaf>(
    value: Leaf(84),
    child: <something>
  ),
)

这允许使用以下方法独立获取每个值:

This allows to obtain each value independently using:

Provider.of<Root>(context)
Provider.of<Leaf>(context);

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