Flutter NowPlaying 示例提供程序错误

Question

我正在努力处理一些 flutter 代码，尤其是 streamprovider。

https://pub.dev/packages/nowplaying/example

我在新的 flutter 项目中尝试了这段代码，但它一直在抛出错误。

你能帮我解决这个错误吗？

错误代码如下：

══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════ The following ProviderNotFoundException was thrown building Consumer(dirty): Error: Could not find the correct Provider above this Consumer Widget

This happens because you used a BuildContext that does not include the provider of your choice. There are a few common scenarios:
You added a new provider in your main.dart and performed a hot-reload. To fix, perform a hot-restart.

The provider you are trying to read is in a different route.

Providers are "scoped". So if you insert of provider inside a route, then other routes will not be able to access that provider.
You used a BuildContext that is an ancestor of the provider you are trying to read.

Make sure that Consumer is under your MultiProvider/Provider. This usually happens when you are creating a provider and trying to read it immediately.

For example, instead of:
  return Provider<Example>(
    create: (_) => Example(),
    // Will throw a ProviderNotFoundError, because `context` is associated
    // to the widget that is the parent of `Provider<Example>`
    child: Text(context.watch<Example>()),
  ),   }   ```

consider using `builder` like so:

```   Widget build(BuildContext context) {
  return Provider<Example>(
    create: (_) => Example(),
    // we use `builder` to obtain a new `BuildContext` that has access to the provider
    builder: (context) {
      // No longer throws
      return Text(context.watch<Example>()),
    }
  ),   }   ```

Answer 1

示例中有几件事让我感到惊讶：

示例省略了 create: (_) => Example(), 部分。为此尝试添加：create: (_) => NowPlayingTrack(),
确保将 initialValue: null, 添加为提供程序包，因为版本 5.0.0-nullsafety 需要 initialData for both FutureProvider and StreamProvider.
参考provider docs:

"To expose a newly created object, use the default constructor of a provider. Do not use the .value constructor if you want to create an object, or you may otherwise have undesired side effects"

这也意味着您不应该使用 value: NowPlaying.instance.stream, 来创建您的对象，而是创建 create 中的一个新对象（参见 1.）。

该示例未指定具体的提供程序类型，这可能会导致问题。试试这个：StreamProvider<NowPlayingTrack>(...)

Flutter NowPlaying 示例提供程序错误

Flutter NowPlaying Example Provider Error

provider

flutter