如何在整个颤振项目中使用 json 对象之一？

Posted 2023-02-23

【中文标题】如何在整个颤振项目中使用 json 对象之一？

【英文标题】：How can i use one of the json object in the whole of my flutter project?

【发布时间】：2020-11-13 17:08:39

【问题描述】：

我从 JSON 获取一些数据，我想在我的 JSON 数据中搜索它以防止出现任何错误（如果我要查找的项目，我没有使用它，否则我会在我的程序中使用它）。

这是我的代码，但我不知道为什么会出现错误！

还有一个问题： 我如何在整个程序中存储像 ["daily"][0]["name"] 这样的项目，因为我的 JSON 中的（每日）项目是我想要的一种项目，另一种是特殊功能或社区或特色。

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


class ItemShop extends StatefulWidget 
  static final String id = 'itemShop';

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


var item;

class _ItemShopState extends State<ItemShop> 

  var item;

  Future fetchItems () async

    http.Response response = await http.get('https://fortniteapi.io/shop?lang=en' , headers: "Authorization" : "97206de0-b1819688-6af9c8d0-d5ded771");


    if (response.statusCode == 200) 
      Map<String , dynamic> item = jsonDecode(response.body);
      this.setState(() 
        item = item;
      );
    

  

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

    fetchItems();
  

  @override
  Widget build(BuildContext context) 


    return Scaffold(
      appBar: AppBar(
        title: Text('ItemShop'),
      ),
      body: Container(
        color: Colors.blue,
        child: Card(
            child: Text(jsonDecode(item)['daily'][0]['name']),
          )
        ),
    );
  

【问题讨论】：

能否请您在问题中包含错误？

能否请您在问题中包含错误？

如果您想在整个项目中使用该项目，请尝试将其存储在本地数据库中，例如：共享偏好或 SQFLite，或者您可以继续通过所有小部件传递该项目。

当我使用 jsonDecode(item)['daily'][0]['name'] 时出现此错误：

我答错了请看。

【参考方案1】：

这个错误发生在我使用 jsonDecode(item)['daily'][0]['name]

Restarted application in 1,711ms.
I/flutter ( 3468): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter ( 3468): The following NoSuchMethodError was thrown building ItemShop(dirty, state: _ItemShopState#93ef8):
I/flutter ( 3468): The getter 'length' was called on null.
I/flutter ( 3468): Receiver: null
I/flutter ( 3468): Tried calling: length
I/flutter ( 3468): The relevant error-causing widget was:
I/flutter ( 3468):   ItemShop file:///D:/ArenaApplicationFlutter/arena/lib/main.dart:15:36
I/flutter ( 3468): When the exception was thrown, this was the stack:
I/flutter ( 3468): #0      Object.noSuchMethod (dart:core-patch/object_patch.dart:53:5)
I/flutter ( 3468): #1      _parseJson (dart:convert-patch/convert_patch.dart:30:28)
I/flutter ( 3468): #2      JsonDecoder.convert (dart:convert/json.dart:505:36)
I/flutter ( 3468): #3      JsonCodec.decode (dart:convert/json.dart:153:41)
I/flutter ( 3468): #4      jsonDecode (dart:convert/json.dart:96:10)
I/flutter ( 3468): #5      _ItemShopState.build (package:arena/Screens/itemShop.dart:51:25)
I/flutter ( 3468): #6      StatefulElement.build (package:flutter/src/widgets/framework.dart:4619:28)
I/flutter ( 3468): #7      ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4502:15)
I/flutter ( 3468): #8      StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4675:11)
I/flutter ( 3468): #9      Element.rebuild (package:flutter/src/widgets/framework.dart:4218:5)
I/flutter ( 3468): #10     ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:4481:5)
I/flutter ( 3468): #11     StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:4666:11)
I/flutter ( 3468): #12     ComponentElement.mount (package:flutter/src/widgets/framework.dart:4476:5)
I/flutter ( 3468): ...     Normal element mounting (115 frames)
I/flutter ( 3468): #127    Element.inflateWidget (package:flutter/src/widgets/framework.dart:3446:14)
I/flutter ( 3468): #128    MultiChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:5947:32)
I/flutter ( 3468): ...     Normal element mounting (253 frames)
I/flutter ( 3468): #381    Element.inflateWidget (package:flutter/src/widgets/framework.dart:3446:14)
I/flutter ( 3468): #382    Element.updateChild (package:flutter/src/widgets/framework.dart:3214:18)
I/flutter ( 3468): #383    RenderObjectToWidgetElement._rebuild (package:flutter/src/widgets/binding.dart:1148:16)
I/flutter ( 3468): #384    RenderObjectToWidgetElement.mount (package:flutter/src/widgets/binding.dart:1119:5)
I/flutter ( 3468): #385    RenderObjectToWidgetAdapter.attachToRenderTree.<anonymous closure> (package:flutter/src/widgets/binding.dart:1061:17)
I/flutter ( 3468): #386    BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2607:19)
I/flutter ( 3468): #387    RenderObjectToWidgetAdapter.attachToRenderTree (package:flutter/src/widgets/binding.dart:1060:13)
I/flutter ( 3468): #388    WidgetsBinding.attachRootWidget (package:flutter/src/widgets/binding.dart:941:7)
I/flutter ( 3468): #389    WidgetsBinding.scheduleAttachRootWidget.<anonymous closure> (package:flutter/src/widgets/binding.dart:922:7)
I/flutter ( 3468): (elided 11 frames from class _RawReceivePortImpl, class _Timer, dart:async, and dart:async-patch)
I/flutter ( 3468): ════════════════════════════════════════════════════════════════════════════════════════════════════
════════ Exception caught by widgets library ═══════════════════════════════════════════════════════
The following NoSuchMethodError was thrown building ItemShop(dirty, state: _ItemShopState#93ef8):
The getter 'length' was called on null.
Receiver: null
Tried calling: length
The relevant error-causing widget was: 
  ItemShop file:///D:/ArenaApplicationFlutter/arena/lib/main.dart:15:36
When the exception was thrown, this was the stack: 
#0      Object.noSuchMethod (dart:core-patch/object_patch.dart:53:5)
#1      _parseJson (dart:convert-patch/convert_patch.dart:30:28)
#2      JsonDecoder.convert (dart:convert/json.dart:505:36)
#3      JsonCodec.decode (dart:convert/json.dart:153:41)
#4      jsonDecode (dart:convert/json.dart:96:10)
...
════════════════════════════════════════════════════════════════════════════════════════════════════
════════ Exception caught by widgets library ═══════════════════════════════════════════════════════
The following NoSuchMethodError was thrown building ItemShop(dirty, state: _ItemShopState#93ef8):
The getter 'length' was called on null.
Receiver: null
Tried calling: length
The relevant error-causing widget was: 
  ItemShop file:///D:/ArenaApplicationFlutter/arena/lib/main.dart:15:36
When the exception was thrown, this was the stack: 
#0      Object.noSuchMethod (dart:core-patch/object_patch.dart:53:5)
#1      _parseJson (dart:convert-patch/convert_patch.dart:30:28)
#2      JsonDecoder.convert (dart:convert/json.dart:505:36)
#3      JsonCodec.decode (dart:convert/json.dart:153:41)
#4      jsonDecode (dart:convert/json.dart:96:10)
...
════════════════════════════════════════════════════════════════════════════════════════════════════