flutter - LateError (LateInitializationError : Field 'latitude' has not been initialized.)

Question

这是我的代码

import 'package:flutter/material.dart';
import 'package:climate/services/location.dart';
import 'package:http/http.dart' as http;
import 'dart:convert';

const apiKey = '78c0a5319f932d3e171aa34ab51dd7e3';

class LoadingScreen extends StatefulWidget {
  @override
  _LoadingScreenState createState() => _LoadingScreenState();
}

class _LoadingScreenState extends State<LoadingScreen> {
  late double latitude;
  late double longitude;
  @override
  void initState() {
    super.initState();
    getLocation();
  }

  void getLocation() async {
    Location location = Location();
    await location.getCurrentLocation();
    latitude = location.latitude;
    longitude = location.longitude;
  }

  void getData() async {
    http.Response reponse = await http.get(Uri.parse(
        "https://api.openweathermap.org/data/2.5/weather?lat=$latitude&lon=$longitude&appid=$apiKey"));

    if (reponse.statusCode == 200) {
      String data = reponse.body;

      int condition = jsonDecode(data)['weather'][0]['id'];
      print(condition);
      double temp = jsonDecode(data)['main']['temp']; //main.temp
      print(temp);
      String city = jsonDecode(data)['name']; //name
      print(city);
    } else {
      print(reponse.statusCode);
    }
    print(reponse.body);
  }

  @override
  Widget build(BuildContext context) {
    getData();
    return Scaffold();
  }
}

问题是它说经度和纬度需要延迟初始化，当我延迟删除时它会抛出一个错误，说需要初始化。

我正在尝试使用 flutter 构建一个天气应用程序，但它一直抛出此错误，我尝试删除 late 修饰符，但随后它抛出一个错误，指出需要初始化。但如果我保留 late 修饰符，它会显示 LateError:

LateInitializationError: Field 'latitude' has not been initialized

Answer 1

可空变量是您想要的，而不是延迟变量。要检查是否已初始化某些内容，您应该使用可为 null 的变量，并且您的代码已经设置好执行此操作。

改变

late MyData data;

到

MyData? data;