Question

我是Flutter / Dart的新手，所以可能没有使用所有正确的关键词，但我遇到了一个问题，我在课程'FirstPageState'扩展状态下得到一条红线。这使我无法调试应用程序，因此我来到这里希望能够获得解决方案！

这是我的'FirstPage.dart'代码

import 'dart:async';

import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;

String _FirstPageText = 'Exchange Rates';

class First extends StatefulWidget {
  // This widget is the root of your application.
  @override
  FirstPageState createState() => new FirstPageState();
  Widget build(BuildContext context) {
    return new MaterialApp(
      home: new Scaffold(
        appBar: new AppBar(
          title: new Text(_FirstPageText),
          centerTitle: true,
          backgroundColor: Colors.black,
        ),
        body: new FeedWidget(),
        ),
      );
  }
}

class FirstPageState extends State<First> {

Future<String> getData() async {
  var response = await http.get(
    'https://jsonplaceholder.typicode.com/posts'
  );

}

}

谢谢你：）

Answer 1

如果您阅读＆＃34;红线＆＃34;，您会看到错误，可能是State an abstract class期待one or more methods to be defined的错误：

实例，getter和setter方法可以是抽象的，定义一个接口，但将其实现留给其他类

在这种情况下，我相信State expects the build method。您可能需要查看documentation behind StatefulWidget，其中描述了必要的内容：

class YellowBird extends StatefulWidget {
  const YellowBird({ Key key }) : super(key: key);

  @override
  _YellowBirdState createState() => new _YellowBirdState();
}

class _YellowBirdState extends State<YellowBird> {
  @override
  Widget build(BuildContext context) {
    return new Container(color: const Color(0xFFFFE306));
  }
}

Answer 2

您从State＆lt; ...＆gt;延伸的任何课程必须覆盖build（）方法。你已经在错误的地方和错误的方式覆盖了build（）方法。

您只需更新代码，如下所示，您的代码就可以使用。

class First extends StatefulWidget {
  @override
  FirstPageState createState() => new FirstPageState();
}
class FirstPageState extends State<First> {

  Future<String> getData() async {
    var response = await http.get(
        'https://jsonplaceholder.typicode.com/posts'
    );
  }

  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      home: new Scaffold(
        appBar: new AppBar(
          title: new Text(_FirstPageText),
          centerTitle: true,
          backgroundColor: Colors.black,
        ),
        body: new FeedWidget(),
      ),
    );
  }
}

Flutter Class不工作

2 个答案: