Flutter - 使用 laravel 获取方法 api

Question

我有颤振的应用程序，我正在尝试调用 api，并获取 json，但它不适用于我

它向我显示了这个错误 I/flutter (13300)：在 null 上调用了 getter 'length'。 I/颤振（13300）：接收器：空 I/flutter (13300)：尝试调用：长度

模型 Category_list.dart

class Category {
  List<Data> data;
  String status;
   Category({this.data, this.status});

  factory Category.fromJson(Map<String, dynamic> json) {
    var list1=json['data'] as List;
    List<Data> data= list1.map((i)=> Data.fromJson(i)).toList();
    return Category(
      data: data,
      status: json['status']
    );
  }
}

class Data {
  int id;
  String name;
  String image;
  String items;

  Data({this.id, this.name, this.image, this.items});

  factory Data.fromJson(Map<String, dynamic> json) {
    return Data(
      id: json['id'],
      name: json['name'],
      image: json['image'],
      items: json['items'],
    );
  }
}

服务 Category_list_services.dart

import 'dart:convert';
import 'package:scoped_model/scoped_model.dart';
import 'dart:async' as future;
import 'package:dio/dio.dart';
import 'package:shared_preferences/shared_preferences.dart';
import '../Models/Category_list.dart';

class CategoryListModel extends Model {
  bool _CategoryLoading = false;
  Category _category;

  bool get CategoryLoading => _CategoryLoading;

  Dio dio = Dio();

  Future<Response<dynamic>> getCategory() async {
    _CategoryLoading = true;
    notifyListeners();
    final SharedPreferences prefs = await SharedPreferences.getInstance();
    dio.options.headers = {'lang': 'en', 'Authorization': prefs.get('token')};
    dio.options.baseUrl = "I put here my api url";

    return await dio.get('/category/list');
  }

  Future<Category> loadCategoryResponse() async {
    var jsonString, jsonResponse;
    try {
      jsonString = await getCategory();

      jsonResponse = json.decode(jsonString.toString());
      print(jsonResponse);
      _category = Category.fromJson(jsonResponse);
      if (jsonString.statusCode >= 200 && jsonString.statusCode < 300) {
       _CategoryLoading = true;
        notifyListeners();
        return _category;
      } else {
        throw Exception("atefffffffffffffffff");
//        _CategoryLoading = false;
//        notifyListeners();
//
//        return _category;
      }
    } on DioError catch (e) {
      if (e.response != null) {
        _CategoryLoading = false;
        notifyListeners();
      }
    }

    return _category;
  }
}

屏幕分类页面.dart

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import '../Models/Category_list.dart';
import '../Scoped_model/main_model.dart';

class CategoriesPage extends StatefulWidget {
  @override
  _CategoriesPageState createState() => _CategoriesPageState();
}

class _CategoriesPageState extends State<CategoriesPage> {
  MainModel model = MainModel();
  Category category = Category();
  var dataa;
  @override
  void initState() {
    model.loadCategoryResponse().then((data){
      setState(() {
         this.dataa= data;

      });
    }

    );
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return Scaffold(
        backgroundColor: Theme.of(context).primaryColor,
        appBar: AppBar(
          backgroundColor: Theme.of(context).accentColor,
          elevation: 0.0,
          title: Text(
            " الاقسام",
            style: TextStyle(
              color: Colors.white,
            ),
          ),
          centerTitle: true,
          leading: Icon(
            Icons.search,
            color: Colors.white,
          ),
        ),
        endDrawer: Drawer(
          child: Container(
            color: Theme.of(context).accentColor,
            child: Directionality(
              textDirection: TextDirection.rtl,
              child: Center(
                child: ListView(
                  children: <Widget>[
                    SizedBox(
                      height: 100,
                    ),
                    //------------------home----------
                    ListTile(
                      onTap: () {
                        Navigator.of(context).pushNamed("/homepage");
                      },
                      title: Text(
                        "الصفحة الرئيسية",
                        style: TextStyle(
                          color: Colors.white,
                        ),
                      ),
                      leading: Icon(
                        Icons.home,
                        color: Colors.white,
                      ),
                    ),
                    //------------------latest--------------
                    SizedBox(
                      height: 7,
                    ),
                    ListTile(
                      onTap: () {
                        Navigator.of(context).pushNamed("/latest");
                      },
                      title: Text(
                        "الاخيرة",
                        style: TextStyle(
                          color: Colors.white,
                        ),
                      ),
                      leading: Icon(
                        Icons.view_list,
                        color: Colors.white,
                      ),
                    ),
                    //--------------------Popular---------
                    SizedBox(
                      height: 7,
                    ),
                    ListTile(
                      onTap: () {
                        Navigator.of(context).pushNamed("/popular");
                      },
                      title: Text(
                        "شائع",
                        style: TextStyle(
                          color: Colors.white,
                        ),
                      ),
                      leading: Icon(
                        Icons.local_florist,
                        color: Colors.white,
                      ),
                    ),
                    //--------------rated------------
                    SizedBox(
                      height: 7,
                    ),
                    ListTile(
                      onTap: () {
                        Navigator.of(context).pushNamed("/rated");
                      },
                      title: Text(
                        "تقيم",
                        style: TextStyle(
                          color: Colors.white,
                        ),
                      ),
                      leading: Icon(
                        Icons.group,
                        color: Colors.white,
                      ),
                    ),
                    //-----------------categories--------------
                    SizedBox(
                      height: 7,
                    ),
                    ListTile(
                      onTap: () {
                        Navigator.pop(context);
                      },
                      title: Text(
                        "الاقسام",
                        style: TextStyle(
                          color: Colors.white,
                        ),
                      ),
                      leading: Icon(
                        Icons.folder_open,
                        color: Colors.white,
                      ),
                    ),

//---------------------Gifs-------------
                    SizedBox(
                      height: 7,
                    ),
                    ListTile(
                      onTap: () {
                        Navigator.of(context).pushNamed("/Gif");
                      },
                      title: Text(
                        "شائع",
                        style: TextStyle(
                          color: Colors.white,
                        ),
                      ),
                      leading: Icon(
                        Icons.gif,
                        color: Colors.white,
                      ),
                    ),
                    //----------------favourite-------------------
                    SizedBox(
                      height: 7,
                    ),
                    ListTile(
                      onTap: () {
                        Navigator.of(context).pushNamed('/favourite');
                      },
                      title: Text(
                        "المفضلة",
                        style: TextStyle(
                          color: Colors.white,
                        ),
                      ),
                      leading: Icon(
                        Icons.favorite_border,
                        color: Colors.white,
                      ),
                    ),
                    //--------------profile---------------
                    SizedBox(
                      height: 7,
                    ),
                    ListTile(
                      onTap: () {
                        Navigator.of(context).pushNamed('/profile');
                      },
                      title: Text(
                        "الصفحة الشخصية",
                        style: TextStyle(
                          color: Colors.white,
                        ),
                      ),
                      leading: Icon(
                        Icons.person_pin_circle,
                        color: Colors.white,
                      ),
                    ),
                    //---------------settings-------------
                    SizedBox(
                      height: 7,
                    ),
                    ListTile(
                      onTap: () {},
                      title: Text(
                        "الاعدادات",
                        style: TextStyle(
                          color: Colors.white,
                        ),
                      ),
                      leading: Icon(
                        Icons.settings,
                        color: Colors.white,
                      ),
                    ),
                    //-----------------login--------------
                    SizedBox(
                      height: 7,
                    ),
                    ListTile(
                      onTap: () {
                        Navigator.of(context).pushNamed("/singin");
                      },
                      title: Text(
                        "تسجيل خروج",
                        style: TextStyle(
                          color: Colors.white,
                        ),
                      ),
                      leading: Icon(
                        Icons.settings_backup_restore,
                        color: Colors.white,
                      ),
                    ),
                  ],
                ),
              ),
            ),
          ),
        ),
        body: GridView.builder(
            shrinkWrap: true,
            scrollDirection: Axis.vertical,
            gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
                crossAxisCount: 3, crossAxisSpacing: 3, mainAxisSpacing: 3),
           itemCount: dataa.length,
            itemBuilder: (BuildContext context,int index) {
              return gridItem(dataa[index].name,
                  dataa[index].image,dataa[index].items);
            }));
  }

  Widget gridItem(String text, String photo, String item) {
    return Stack(
      children: <Widget>[
        Container(
          height: 150,
          width: 150,
          decoration: BoxDecoration(
              borderRadius: BorderRadius.circular(60),
              image:
                  DecorationImage(image: AssetImage(photo), fit: BoxFit.cover),
              color: Colors.red),
          child: Align(
            alignment: Alignment.center,
            child: Padding(
              padding: const EdgeInsets.only(top: 25),
              child: Column(
                children: <Widget>[
                  Text(
                    text,
                    style: TextStyle(
                      color: Colors.white,
                    ),
                  ),
                  Text(
                    item,
                    style: TextStyle(
                      color: Colors.white,
                    ),
                  ),
                ],
              ),
            ),
          ),
        )
      ],
    );
  }
}

Answer 1

我不确定，但它看起来像是代码中的错误。

class _CategoriesPageState extends State<CategoriesPage> {
  MainModel model = MainModel(); <--- this one

应该是：

CategoryListModel model = new CategoryListModel();

Answer 2

我认为问题在于您没有在构造 CategoryListModel 时实例化 dataa，这意味着它为空（根据错误猜测，对 Dart 不太熟悉）。所以在请求响应中设置 dataa 之前，这一行：

temCount: dataa.length,

在 null 上调用 .length。

相反，我建议将dataa 实例化为一个空数组，如下所示：

// ...
Category category = Category();
dataa = [];
// ...