Flutter从自定义TextFormField添加值，并自动在另一个自定义文本表单字段中显示该值

class CustomTextField extends StatefulWidget {
  @override
  _CustomTextFieldState createState() => _CustomTextFieldState();
}

class _CustomTextFieldState extends State<CustomTextField> {
  String _value = '';

  @override
  Widget build(BuildContext context) {
    return TextFormField(
      onChanged: (value) {
        setState(() {
          _value = value;
        });
      },
    );
  }
}

class CustomDisplayField extends StatelessWidget {
  final String value;

  CustomDisplayField(this.value);

  @override
  Widget build(BuildContext context) {
    return Text(value);
  }
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: [
              CustomTextField(),
              CustomDisplayField(_value),
            ],
          ),
        ),
      ),
    );
  }
}