Flutter无法识别有效导入

Question

我有一个简单的Flutter应用程序。

import 'package:flutter/material.dart';

void main() => runApp(App());

class App extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Welcome to Flutter',
      home: Scaffold(
        appBar: AppBar(
          title: Text('Sample'),
        ),
        body: Center(
          child: Column (
            children: <Widget>[
              CustomCard(mainTitle: "A simple widget!"),
            ]
          )
        ),
      ),
    );
  }
}

class CustomCard extends StatelessWidget {
  final String mainTitle;

  CustomCard({@required this.mainTitle});

  @override
  Widget build(BuildContext context) {
    return Container(
      height: 48,
      width: 200,
      child: Text('$mainTitle'),
    );
  }
}

如果我将CustomCard类移动到另一个文件中，例如custom_card.dart，然后执行导入'package:myproject/custom_card.dart'，我会得到错误消息:“the parameter mainTitle is not defined”。如果类CustomCard留在main.dart中，那么一切都可以工作。我错过了什么？

Answer 1

包:myproject/custom_card.dart是对包根目录下lib/custom_card.dart的引用。您还需要确保MyProject部分与pubspec.yaml文件中的包名匹配。见https://www.dartlang.org/tools/pub/package-layout#public-libraries