class - flutter 类不工作

Question

我是 Flutter/Dart 的新手，所以可能没有使用所有正确的关键字，但我遇到了一个问题，我在类 'FirstPageState' extends State 下得到了一条红线.这会阻止我调试应用程序，所以我来到这里希望能得到解决方案!

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“红线”，您会看到一个错误，可能是 State 为 an abstract class期望 one or more methods to be defined :

Instance, getter, and setter methods can be abstract, defining an interface but leaving its implementation up to other classes

在这种情况下，我相信State expects the build method .你可能想看看 documentation behind StatefulWidget ，它描述了什么是必要的:

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));
  }
}