如何从flutter中调用需要上下文的函数、从外部调用、从内部调用

void myFunction(BuildContext context) {
  // 使用BuildContext来执行需要上下文的操作
  Scaffold.of(context).showSnackBar(SnackBar(content: Text('Hello World')));
}

class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return RaisedButton(
      onPressed: () {
        // 调用需要上下文的函数
        myFunction(context);
      },
      child: Text('Call Function'),
    );
  }
}

class MyWidget extends StatefulWidget {
  // 创建一个全局的Key
  static final GlobalKey<ScaffoldState> scaffoldKey = GlobalKey<ScaffoldState>();

  @override
  _MyWidgetState createState() => _MyWidgetState();
}

class _MyWidgetState extends State<MyWidget> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      key: MyWidget.scaffoldKey,
      body: RaisedButton(
        onPressed: () {
          // 通过GlobalKey来调用需要上下文的函数
          MyWidget.scaffoldKey.currentState.showSnackBar(SnackBar(content: Text('Hello World')));
        },
        child: Text('Call Function'),
      ),
    );
  }
}

typedef MyFunction = void Function();

class MyWidget extends StatelessWidget {
  final MyFunction onCallFunction;

  MyWidget({this.onCallFunction});

  @override
  Widget build(BuildContext context) {
    return RaisedButton(
      onPressed: () {
        // 调用回调函数
        onCallFunction();
      },
      child: Text('Call Function'),
    );
  }
}

// 外部调用函数的示例
void externalFunction() {
  print('Called from external');
}

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: MyWidget(
          onCallFunction: externalFunction,
        ),
      ),
    );
  }
}

void myFunction() {
  print('Called from external');
}

class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return RaisedButton(
      onPressed: () {
        // 调用全局函数
        myFunction();
      },
      child: Text('Call Function'),
    );
  }
}

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: MyWidget(),
      ),
    );
  }
}

class MyWidget extends StatelessWidget {
  void internalFunction() {
    print('Called from internal');
  }

  @override
  Widget build(BuildContext context) {
    return RaisedButton(
      onPressed: () {
        // 调用内部函数
        internalFunction();
      },
      child: Text('Call Function'),
    );
  }
}

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: MyWidget(),
      ),
    );
  }
}