英文:
How can I access class methods from a different file in Flutter?
问题
以下是翻译好的内容：
我在一个名为 `main.dart` 的文件中有一个简单的类 `MyApp`，其中包含两个函数（`setLocale`、`setThemeMode`）。
```dart
class MyApp extends StatefulWidget {
const MyApp({super.key});
@override
State<MyApp> createState() => _MyAppState();
static State<MyApp> of(BuildContext context) =>
context.findAncestorStateOfType<_MyAppState>()!;
}
class _MyAppState extends State<MyApp> {
void setLocale(String language) {}
void setThemeMode(ThemeMode mode) {}
}
我想在不同文件 flutter_flow.dart 中的函数中使用它们（没有类，只有这些函数）。
void setAppLanguage(BuildContext context, String language) =>
MyApp.of(context).setLocale(language);
void setDarkModeSetting(BuildContext context, ThemeMode themeMode) =>
MyApp.of(context).setThemeMode(themeMode);
但我遇到了以下错误。
The method 'setLocale' isn't defined for the type 'State'. Try correcting the name to the name of an existing method, or defining a method named 'setLocale'.
据我理解，文件似乎无法识别这些方法，尽管我已导入包含 MyApp 类的文件。我可以请教一下，应该怎么做，从哪里寻找解决方案？
<details>
<summary>英文:</summary>
I've got a simple class `MyApp` in a `main.dart` file, with two functions in it (`setLocale`, `setThemeMode`).
class MyApp extends StatefulWidget {
const MyApp({super.key});
@override
State<MyApp> createState() => _MyAppState();
static State<MyApp> of(BuildContext context) =>
context.findAncestorStateOfType<_MyAppState>()!;
}
class _MyAppState extends State<MyApp> {
void setLocale(String language) {}
void setThemeMode(ThemeMode mode) {}
}
And I would like to use them within functions in different file `flutter_flow.dart` (no class, clean file with these functions).
void setAppLanguage(BuildContext context, String language) =>
MyApp.of(context).setLocale(language);
void setDarkModeSetting(BuildContext context, ThemeMode themeMode) =>
MyApp.of(context).setThemeMode(themeMode);
And I'm stuck with this error.
`The method 'setLocale' isn't defined for the type 'State'. Try correcting the name to the name of an existing method, or defining a method named 'setLocale'.`
As far as I understand, file does not see this methods although I'm importing file with class MyApp. May I ask for help, what to do, where to search for solution?
</details>
# 答案1
**得分**: 0
你需要将以下代码中的返回类型更改为：
```dart
_MyAppState of(BuildContext context)
使用您当前的代码，当您执行以下操作时：
MyApp.of(context)
它返回类型为 State<MyApp>，这是通用的 State 类，来自 Flutter，它不包含任何自定义方法。
当您将 of(BuildContext context) 的返回类型更改为 _MyAppState 时，MyApp.of(context) 将返回 _MyAppState 类型。Dart 分析器知道它具有您的自定义方法 setLocale 和 setThemeMode，不再会抛出错误。
英文:
You need to change the return type of
State<MyApp> of(BuildContext context)
to
_MyAppState of(BuildContext context)
With your current code, when you do
MyApp.of(context)
it returns the type State<MyApp> which is the generic State class from flutter which won't contain any of your custom methods.
When you change the return of of(BuildContext context) to _MyAppState, MyApp.of(context) will return _MyAppState type. The dart analyzer knows that it has your custom methods setLocale and setThemeMode and won't throw an error anymore.
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