flutter: You used a `BuildContext` that is an ancestor of the provider you are trying to read

当在StatefulWidget中使用ChangeNotifierProvider绑定ViewModel，就会报如上错误，完整的错误日志如下 

 

Error: Could not find the correct Provider<RecordTopViewModel> above this RecordTop Widget

This likely happens because you used a `BuildContext` that does not include the provider
of your choice. There are a few common scenarios:

- 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 RecordTop is under your MultiProvider/Provider<RecordTopViewModel>.
  This usually happen when you are creating a provider and trying to read it immediately.

  For example, instead of:

  ```
  Widget build(BuildContext context) {
    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>()),
      }
    ),
  }
  ```

If none of these solutions work, consider asking for help on *:
https://*.com/questions/tagged/flutter

解决方案：在布局最外层，用Consumer<ViewModel>(builder:XXX)包裹上：

  child: Consumer<RecordTopViewModel>(builder: (context, value, child) {
          return Scaffold(
)