运行天气应用程序时出现此错误我正在使用 json 和 http 库来获取数据但我不知道为啥会出现此错误

Posted 2023-02-23

【中文标题】运行天气应用程序时出现此错误我正在使用 json 和 http 库来获取数据但我不知道为啥会出现此错误

【英文标题】：This error appears when running the weather app I am using json and http library to fetch data but I don't know why this error appears运行天气应用程序时出现此错误我正在使用 json 和 http 库来获取数据但我不知道为什么会出现此错误

【发布时间】：2021-01-15 16:15:36

【问题描述】：

错误代码

E/flutter (25456): [错误:flutter/lib/ui/ui_dart_state.cc(157)] 未处理的异常：NoSuchMethodError：调用了方法“[]” 空值。 E/flutter (25456): 接收器: null E/flutter (25456): 试过 调用：E/flutter（25456）：#0 Object.noSuchMethod (dart:core-patch/object_patch.dart:53:5) E/flutter (25456): #1 _WeatherState.fetchLocationUpDate。 （包：tast_project/screenes/screenweather.dart:31:27）E/flutter (25456): #2 状态.setState (包:flutter/src/widgets/framework.dart:1148:30) E/flutter (25456): #3 _WeatherState.fetchLocationUpDate （包：tast_project/screenes/screenweather.dart:30:5）E/flutter (25456): E/颤振 (25456): #4 _WeatherState.initState (package:tast_project/screenes/screenweather.dart:42:5) E/flutter (25456)：#5 StatefulElement._firstBuild (包:flutter/src/widgets/framework.dart:4355:58) E/flutter (25456)：#6 ComponentElement.mount (包:flutter/src/widgets/framework.dart:4201:5) E/flutter (25456): #7 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3194:14) E/flutter (25456): #8 元素.updateChild (包:flutter/src/widgets/framework.dart:2988:12) E/flutter (25456)：#9 SingleChildRenderObjectElement.mount (包:flutter/src/widgets/framework.dart:5445:14) E/flutter (25456): #10 元素.inflateWidget (包:flutter/src/widgets/framework.dart:3194:14) E/flutter (25456): #11 元素.updateChild (包:flutter/src/widgets/framework.dart:2988:12) E/flutter （25456）：#12 ComponentElement.performRebuild (包:flutter/src/widgets/framework.dart:4243:16) E/flutter (25456)：#13 元素重建 (包:flutter/src/widgets/framework.dart:3947:5) E/flutter (25456): #14 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:4206:5) E/flutter (25456): #15 ComponentElement.mount (package:flutter/src/widgets/framework.dart:4201:5) E/flutter (25456): #16 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3194:14) E/flutter (25456)：#17 元素.updateChild (包:flutter/src/widgets/framework.dart:2988:12) E/flutter (25456)：#18 SingleChildRenderObjectElement.mount (包:flutter/src/widgets/framework.dart:5445:14) E/flutter （25456）：#19 元素.inflateWidget (包:flutter/src/widgets/framework.dart:3194:14) E/flutter (25456): #20 元素.updateChild (包:flutter/src/widgets/framework.dart:2988:12) E/flutter (25456): #21 SingleChildRenderObjectElement.mount (包:flutter/src/widgets/framework.dart:5445:14) E/flutter （25456）：#22 元素.inflateWidget (包:flutter/src/widgets/framework.dart:3194:14) E/flutter (25456): #23 元素.updateChild (包:flutter/src/widgets/framework.dart:2988:12) E/flutter （25456）：#24 ComponentElement.performRebuild (包:flutter/src/widgets/framework.dart:4243:16) E/flutter （25456）：#25 元素重建 (包:flutter/src/widgets/framework.dart:3947:5) E/flutter (25456): #26 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:4206:5) E/flutter (25456): #27 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:4381:11) E/flutter （25456）：#28 ComponentElement.mount (包:flutter/src/widgets/framework.dart:4201:5) E/flutter (25456): #29 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3194:14) E/flutter (25456): #30 元素.updateChild (包:flutter/src/widgets/framework.dart:2988:12) E/flutter (25456)：#31 SingleChildRenderObjectElement.mount (包:flutter/src/widgets/framework.dart:5445:14) E/flutter （25456）：#32 元素.inflateWidget (包:flutter/src/widgets/framework.dart:3194:14) E/flutter （25456）：#33 元素.updateChild (包:flutter/src/widgets/framework.dart:2988:12) E/flutter (25456)：#34 SingleChildRenderObjectElement.mount (包:flutter/src/widgets/framework.dart:5445:14) E/flutter （25456）：#35 元素.inflateWidget (包:flutter/src/widgets/framework.dart:3194:14) E/flutter （25456）：#36 元素.updateChild (包:flutter/src/widgets/framework.dart:2988:12) E/flutter （25456）：#37 ComponentElement.performRebuild (包:flutter/src/widgets/framework.dart:4243:16) E/flutter （25456）：#38 元素重建 (包:flutter/src/widgets/framework.dart:3947:5) E/flutter (25456): #39 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:4206:5) E/flutter (25456): #40 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:4381:11) E/flutter （25456）：#41 组件元素.mount (包:flutter/src/widgets/framework.dart:4201:5) E/flutter (25456): #42 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3194:14) E/flutter （25456）：#43 元素.updateChild (包:flutter/src/widgets/framework.dart:2988:12) E/flutter （25456）：#44 ComponentElement.performRebuild （包：flutter/src/widgets/framework.da

   Flutter code weather

  

    import 'package:flutter/cupertino.dart';
    import 'package:flutter/material.dart';
    import 'dart:async';
    import 'package:http/http.dart' as http;
    import 'dart:convert';
    
    class Weather extends StatefulWidget 
      @override
      _WeatherState createState() => _WeatherState();
    
    const ipkay = '14f4090b86e2548527113ccac56a5ae4';
    class _WeatherState extends State<Weather> 
      var temp = 0;
      String city='';
      //var id = 4099194;
      String location ;
      var textEditingController = TextEditingController();
      fetchSearch(String input) async 
          http.Response response = await http.get(
             "http://api.openweathermap.org/data/2.5/weather?units=metric&appid=14f4090b86e2548527113ccac56a5ae4&q=" + input);
          var result = json.decode(response.body);
           setState(() 
             location =result['name'];
           );
    
      fetchLocationUpDate()async
        http.Response response = await http.get(
         'http://api.openweathermap.org/data/2.5/weather?units=metric&appid=14f4090b86e2548527113ccac56a5ae4&q=$location');
        var result = json.decode(response.body);
        setState(() 
          temp =result['main']['temp'];
           city =result['name'];
        );
    
      glo(String city)
        fetchSearch(city);
        fetchLocationUpDate();
    
      @override
      void initState() 
        super.initState();
        fetchLocationUpDate();
    
      @override
      Widget build(BuildContext context) 
        Size size = MediaQuery.of(context).size;
        return Scaffold(
          backgroundColor: Colors.transparent,
          body: SafeArea(
            child: Container(
              width: size.width,
              height: size.height,
              decoration: BoxDecoration(
                  image: DecorationImage(
                      image: AssetImage(
                        'assetes/img/night.jpg',
                      ),
                      fit: BoxFit.fill)),
              child: Column(
                mainAxisAlignment: MainAxisAlignment.center,
                children: <Widget>[
                  Text(
                    '$temp.toString() C°',
                    style: TextStyle(color: Colors.white, fontSize: 30),
                  ),
                  Text(
                    '$city',
                    style: TextStyle(color: Colors.white, fontSize: 30),
                  ),
                  Card(
                    child: TextField(
                      onSubmitted: (String city) 
                        glo(city);
                      ,
                      controller: textEditingController,
                      decoration: InputDecoration(
                        hintText: 'please entre city',
                        prefixIcon: Icon(Icons.search),
                      ),
                    ),
                  ),
                )
                ],
              ),
            ),
          ),
        );
      

  

【参考方案1】：

您可以在下面复制粘贴运行完整代码 第 1 步：double temp = 0; 第 2 步：glo 需要 async 和 await

glo(String city) async 
    await fetchSearch(city);
    await fetchLocationUpDate();
  

第 3 步：检查城市是否存在

if (result["cod"] == 200) 
      setState(() 
        location = result['name'];
        print("locaton $location");
      );
    

工作演示

完整代码

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

class Weather extends StatefulWidget 
  @override
  _WeatherState createState() => _WeatherState();


const ipkay = '14f4090b86e2548527113ccac56a5ae4';

class _WeatherState extends State<Weather> 
  double temp = 0;
  //var id = 4099194;
  String location;
  var textEditingController = TextEditingController();
  fetchSearch(String input) async 
    http.Response response = await http.get(
        "http://api.openweathermap.org/data/2.5/weather?units=metric&appid=14f4090b86e2548527113ccac56a5ae4&q=" +
            input);
    var result = json.decode(response.body);
    print("fetchSearch $response.body");
    if (result["cod"] == 200) 
      setState(() 
        location = result['name'];
        print("locaton $location");
      );
    
  

  fetchLocationUpDate() async 
    print("location to string $location.toString()");
    http.Response response = await http.get(
        'http://api.openweathermap.org/data/2.5/weather?units=metric&appid=14f4090b86e2548527113ccac56a5ae4&q=' +
            location.toString());
    print("LocationUpdate $response.body");
    var result = json.decode(response.body);
    if (result["cod"] == 200) 
      setState(() 
        temp = result['main']['temp'];
      );
    
  

  glo(String city) async 
    await fetchSearch(city);
    await fetchLocationUpDate();
  

  @override
  void initState() 
    super.initState();
    //fetchLocationUpDate();
  

  @override
  Widget build(BuildContext context) 
    Size size = MediaQuery.of(context).size;
    return Scaffold(
      backgroundColor: Colors.transparent,
      body: SafeArea(
        child: Container(
          width: size.width,
          height: size.height,
          decoration: BoxDecoration(
              image: DecorationImage(
                  image: NetworkImage(
                    'https://picsum.photos/250?image=9',
                  ),
                  fit: BoxFit.fill)),
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Text(
                '$temp.toDouble() C°',
                style: TextStyle(color: Colors.white, fontSize: 30),
              ),
              Card(
                child: TextField(
                  onSubmitted: (String city) 
                    glo(city);
                  ,
                  controller: textEditingController,
                  decoration: InputDecoration(
                    hintText: 'please entre city',
                    prefixIcon: Icon(Icons.search),
                  ),
                ),
              ),
              //              RaisedButton(
              //                onPressed: () 
              //                  glo();
              //                ,
              //              )
            ],
          ),
        ),
      ),
    );
  


void main() 
  runApp(MyApp());


class MyApp extends StatelessWidget 
  @override
  Widget build(BuildContext context) 
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: Weather(),
    );
  


class MyHomePage extends StatefulWidget 
  MyHomePage(Key key, this.title) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();


class _MyHomePageState extends State<MyHomePage> 
  int _counter = 0;

  void _incrementCounter() 
    setState(() 
      _counter++;
    );
  

  @override
  Widget build(BuildContext context) 
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.headline4,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );