找不到提供者 Flutter

Question

我想在不同的小部件之间共享一些数据，因此我决定使用 ChangeNotifierProvider 及其相对的 Consumer。我之前已经使用过 Provider ，但从未以这种方式使用过（事实上我遇到了一些错误）。

ChangeNotifierProvider 已在 menu 页面中定义，而 Consumer 已在 menu 中定义的其他小部件中定义也。

菜单页面：

class Menu extends StatefulWidget {
//...SOme code
ChangeNotifierProvider<Example>(
              create: (context) => Example(),
              child: ShowMultipleAnswers()
//...some code

现在我想在 ShowMultipleAnswers() 小部件中使用 Consumer 来消耗菜单中创建的数据，例如：

class ShowMultipleAnswers extends StatefulWidget {
//...some code
Widget build(BuildContext context) {
    return Consumer<Example>(builder: (context, handler, child) {
//some code

但我遇到了这些错误：

Error: Could not find the correct Provider<Example> above this Consumer<Example> 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.

consider using `builder` like so:
Make sure that Consumer<Example> is under your MultiProvider/Provider<Example>.
  This usually happens 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>()),
    ),
  }
  ```


  ```
  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>()),
      }
    ),
  }
  ```

我认为最重要的是有效选项是 2 ：

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

但我不知道，因为它们应该在同一个中，我的意思是 ShowMultipleAnswers() 是 Provider 子项。 或者第二种

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

在这种情况下，按照上面的建议，我应该使用 builder:(context){} 而不是直接调用 child : .. 但我在提供者之后读到了5 builder 已被 create 取代，所以我很困惑。

如果我使用了错误的小部件，请告诉我！

Answer 1

错误消息准确指定并描述了

使用没有 Example 提供程序的 Menu 上下文构建的 ShowMultipleAnswers 错误，因此它抛出此错误。

您可以使用 builder 属性而不是 child 或使用提供程序包装您的 MaterialApp

您的代码应如下所示：

class Menu extends StatefulWidget {
//...SOme code
ChangeNotifierProvider<Example>(
              create: (context) => Example(),
              builder: (context) {
                 return ShowMultipleAnswers();
              } 
//...some code

Answer 2

我忘了说 Menu 和 ShowMultipleAnswers 之间还有一个页面，就像它们之间的桥梁一样，所以真正的流程是：

Menu Page - > 桥接页面 -> 显示多个答案页面。

我删除了这个Bridge Page并且它成功了！但我仍然不明白为什么它不起作用，也许是因为 Bridge Page 没有任何其 Provider 的引用？