应为“String”类型的值，但得到“Null”类型之一

Question

import 'package:flutter/material.dart';
import 'widgets/main_widget.dart';

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

import 'dart:async';

import 'dart:convert';


Future<WeatherInfo> fetchWeather() async {

  final zipCode = "180007";

  final apiKey = "d415dc7d3cae2e2b8a722dca06eb9e88";

  final requestUrl =
      "http://api.openweathermap.org/data/2.5/weather?zip={zipCode},IN&units=imperial&appid={apiKey}";


  final response = await http.get(Uri.parse(requestUrl));

  return WeatherInfo.fromJson(jsonDecode(response.body));
}


class WeatherInfo {

  final String location;

  final double temp;

  final double tempMin;

  final double tempMax;

  final String weather;

  final int Humidity;

  final double windspeed;

  WeatherInfo(

      {required this.location,

      required this.temp,

      required this.tempMin,

      required this.tempMax,

      required this.weather,

      required this.Humidity,

      required this.windspeed});

  factory WeatherInfo.fromJson(Map<String, dynamic> json) {

    return WeatherInfo(

        location: json['name'],

        temp: json['main']['temp'],

        tempMin: json['main']['temp_min'],

        tempMax: json['main']['temp_max'],

        weather: json['weather']['description'],

        Humidity: json['main']['humidity'],

        windspeed: json['wind']['speed']);

  }
}

void main() => runApp(MaterialApp(title: "Weather App", home: MyApp()));


class MyApp extends StatefulWidget {

  @override

  State<StatefulWidget> createState() {

    return _MyApp();

  }
}

class _MyApp extends State<MyApp> {

  late Future<WeatherInfo> futureWeather;

  @override

  void initState() {

    super.initState();

    futureWeather = fetchWeather();
  }

  @override

  Widget build(BuildContext context) {

    return Scaffold(

        body: FutureBuilder<WeatherInfo>(

            future: futureWeather,

            builder: (context, Snapshot) {

              if (Snapshot.hasData) {

                return MainWidget(

                    location: Snapshot.data!.location,

                    temp: Snapshot.data!.temp,

                    tempMin: Snapshot.data!.tempMin,

                    tempMax: Snapshot.data!.tempMax,

                    weather: Snapshot.data!.weather,

                    Humidity: Snapshot.data!.Humidity,

                    windspeed: Snapshot.data!.windspeed);

              } else if (Snapshot.hasError) {

                return Center(

                  child: Text("${Snapshot.error}"),

                );
              }

              return CircularProgressIndicator();
            }));
  }
}

Answer 1

你应该在调用 fetchweather() 时等待

void initState() {

    super.initState();
    fun();
}

void fun() async {
futureWeather = await fetchWeather();
setState(() {});
  }
}

Answer 2

我在您的代码中发现了两个问题：

1. 如果您打算将 apiKey 和 zipCode 嵌入到 requestUrl 中，则必须在 {apiKey} 和 {zipCode} 之前使用 $。
2. 如果我没记错的话，您会因为 null 安全而收到此错误，您可以通过在类型规范（例如 String？或 double？ )。

但我想如果你解决了第一个问题，那么第二个解决方案就没有必要了，因为我猜你从 API 得到错误响应，导致变量为空，所以打印你得到检查的响应并不要'不要忘记处理错误响应。