使用flutter/Dart时，如何在继承的类中使用BuildContext

import 'package:flutter/material.dart';

class MyWidget extends StatelessWidget {
  final BuildContext context;

  MyWidget(this.context);

  // ...
}

class MyWidget extends StatelessWidget {
  final BuildContext context;

  MyWidget(this.context);

  @override
  Widget build(BuildContext context) {
    return Container(
      child: RaisedButton(
        onPressed: () {
          // 使用BuildContext
          showDialog(
            context: context,
            builder: (BuildContext context) {
              return AlertDialog(
                title: Text('Dialog'),
                content: Text('This is a dialog.'),
                actions: [
                  FlatButton(
                    child: Text('Close'),
                    onPressed: () {
                      Navigator.of(context).pop();
                    },
                  ),
                ],
              );
            },
          );
        },
        child: Text('Show Dialog'),
      ),
    );
  }
}