成员"setState"只能在"package:flutter/src/widgets/framework.dart"子类的实例成员中使用. [英] The member 'setState' can only be used within instance members of subclasses of 'package:flutter/src/widgets/framework.dart'

问题描述

(i18n)我从MyApp类外部使用setState更改语言，收到此警告，但不知道如何解决.

(i18n) I use setState from outside of MyApp class to change language, I got this warning, and don't know how to solve it.

info: The member 'setState' can only be used within instance members of subclasses of 'package:flutter/src/widgets/framework.dart'. (invalid_use_of_protected_member at [flutter_firebase_authen] lib\app.dart:22)

class MyApp extends StatefulWidget {
  final FirebaseAnalyticsObserver observer;

  const MyApp({
    Key key,
    @required this.observer,
  }) : super(key: key);

  @override
  _MyAppState createState() => _MyAppState();

  static void setLocale(BuildContext context, Locale newLocale) {
    final _MyAppState state = context.ancestorStateOfType(const TypeMatcher<_MyAppState>());
    state.setState(() {
      state.locale = newLocale;
    });
  }
}

推荐答案

警告消息非常清楚:函数 setState 只能从该类内部调用，而不能从另一个类调用.

The warning message is quite clear: the function setState should only be called from within the class, not from another class.

解决方法很简单，在 State 类中编写一个帮助程序函数，该函数为您调用 setState .例如:

The workaround is simple, write a helper function inside your State class, that calls setState for you. For example:

refresh() => setState(() {});

现在从此类之外，您可以调用 state.refresh().

Now from outside this class, you can call state.refresh().

(但实际上，如果您要从另一个类调用 setState ，也许您应该研究 ValueNotifier 或 StreamBuilder 等).

(But really, if you are calling setState from another class, maybe you should look into ValueNotifier, or StreamBuilder, etc.)

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