当用户应用程序打开我的应用程序提供 3 个选项餐厅、商店、快递时，我在餐厅部分遇到了这个问题当单击 grcery 时它正常工作，当我单击餐厅按钮时，names.dart 中出现此错误
这里是 names.dart 代码 ```
import 'package:flutter/foundation.dart';
import 'package:http/http.dart' as http;
import 'dart:convert';
import 'dart:math' show cos, sqrt, asin;
class NamesItem {
final String id;
final String name;
final String description;
final List<MenuItem> menu;
final List<DealItem> deal;
final String namesLat;
final String namesLong;
final String address;
final String contact;
final String status;
final List<String> category;
NamesItem({
@required this.id,
@required this.name,
@required this.description,
@required this.menu,
@required this.deal,
this.namesLat,
this.namesLong,
this.address,
this.contact,
this.status,
this.category,
});
}
class MenuItem {
final String id;
final String name;
final double price;
final String description;
final String image;
final String stock;
final String category;
MenuItem({
@required this.id,
@required this.name,
@required this.price,
@required this.description,
this.image,
this.stock,
this.category,
});
}
class DealItem {
final String id;
final String name;
final double price;
final String description;
final String image;
final String stock;
final String category;
DealItem({
@required this.id,
@required this.name,
@required this.price,
@required this.description,
this.image,
this.stock,
this.category,
});
}
class Names with ChangeNotifier {
List<NamesItem> _restaurantNames = [];
List<NamesItem> _shopNames = [];
//Calculates distance in km
double calculateDistance(userLat, userLong, resLat, resLong) {
var p = 0.017453292519943295;
var c = cos;
var a = 0.5 -
c((resLat - userLat) * p) / 2 +
c(userLat * p) * c(resLat * p) * (1 - c((resLong - userLong) * p)) / 2;
return 12742 * asin(sqrt(a));
}
// List<NamesItem> get restaurantNames {
// return [..._restaurantNames];
// }
List<NamesItem> restaurantNames(String userLat, String userLong) {
List<NamesItem> nearestRestaurant = [];
_restaurantNames.forEach((element) {
var distanceBetween = calculateDistance(
double.parse(userLat),
double.parse(userLong),
double.parse(element.namesLat),
double.parse(element.namesLong),
);
//1000 km in distance range will find restaurat
if (distanceBetween < 10) {
nearestRestaurant.add(element);
}
});
return [...nearestRestaurant];
}
List<NamesItem> shopNames(String userLat, String userLong) {
List<NamesItem> nearestShop = [];
_shopNames.forEach((element) {
var distanceBetween = calculateDistance(
double.parse(userLat),
double.parse(userLong),
double.parse(element.namesLat),
**double.parse(element.namesLong)**,
);
//1000 km in distance range will find restaurat
print("$distanceBetween is the distance between 2 places");
if (distanceBetween < 10) {
nearestShop.add(element);
}
});
return [...nearestShop];
}
// List<NamesItem> get shopNames {
// return [..._shopNames];
// }
Map<String, String> getShopInfo(String shopId) {
String name;
String address;
String contact;
_restaurantNames.forEach((element) {
if (element.id == shopId) {
name = element.name;
address = element.address;
contact = element.contact;
}
});
if (name == null) {
_shopNames.forEach((element) {
if (element.id == shopId) {
name = element.name;
address = element.address;
contact = element.contact;
}
});
}
Map<String, String> info = {
"name": name,
"address": address,
"contact": contact
};
return info;
}
List<NamesItem> getRestaurantMenu(String id) {
return _restaurantNames.where((item) => item.id == id).toList();
}
List<NamesItem> getShopMenu(String id) {
return _shopNames.where((item) => item.id == id).toList();
}
List<String> getCategoryOptions(String id) {
List<String> categoryOptions;
_restaurantNames.forEach((rest) {
if (rest.id == id) {
print(rest.category);
categoryOptions = rest.category;
}
});
_shopNames.forEach((shop) {
if (shop.id == id) {
categoryOptions = shop.category;
}
});
return categoryOptions;
}
// List<String> getShopCategoryOptions(String id) {
// _shopNames.forEach((shop) {
// if (shop.id == id) {
// return shop.category;
// }
// });
// return null;
// }
List<String> getLocation(String shopId) {
String lat;
String lng;
_restaurantNames.forEach((item) {
if (item.id == shopId) {
lat = item.namesLat;
lng = item.namesLong;
}
});
_shopNames.forEach((item) {
if (item.id == shopId) {
lat = item.namesLat;
lng = item.namesLong;
}
});
return [lat, lng];
}
Future<void> fetchAndSetNames() async {
final urlRestaurant =
'https://jhola-e90ff.firebaseio.com/registeredShops/restaurants.json';
var responseRestaurant = await http.get(urlRestaurant);
print(responseRestaurant.body);
final List<NamesItem> loadedRestaurant = [];
var extractedRestaurant =
json.decode(responseRestaurant.body) as Map<String, dynamic>;
// print(extractedRestaurant);
if (extractedRestaurant != null) {
extractedRestaurant.forEach((resId, resData) {
// List<DealItem> loadedDeals = [];
loadedRestaurant.add(
NamesItem(
id: resId.toString(),
name: resData['name'].toString(),
description: resData['address'].toString(),
namesLat: resData['lat'].toString(),
namesLong: resData['long'].toString(),
status: resData["loggedIn"].toString(),
address: resData['address'].toString(),
contact: resData['phone'].toString(),
menu: resData["menu"] == null
? []
: (resData["menu"] as Map<String, dynamic>)
.values
.map((e) => MenuItem(
id: e["productId"].toString(),
name: e["productName"].toString(),
price: double.parse(e["productPrice"].toString()),
description: e["productDescription"].toString(),
stock: e["stock"].toString(),
category: e["category_name"].toString(),
image:
"https://firebasestorage.googleapis.com/v0/b/jhola-e90ff.appspot.com/o/images%2F${e['productId'].toString()}?alt=media&token=37e96ab0-172d-4387-88a5-18c508abe70b",
))
.toList(),
deal: resData["deals"] == null
? []
: (resData["deals"] as Map<String, dynamic>)
.values
.map((e) => DealItem(
id: e["productId"].toString(),
name: e["productName"].toString(),
price: double.parse(e["productPrice"].toString()),
description: e["productDescription"].toString(),
stock: e["stock"].toString(),
category: e["category_name"].toString(),
image:
"https://firebasestorage.googleapis.com/v0/b/jhola-e90ff.appspot.com/o/images%2F${e['productId'].toString()}?alt=media&token=37e96ab0-172d-4387-88a5-18c508abe70b",
))
.toList(),
category: resData["categories"] == null
? []
: (resData["categories"] as Map<String, dynamic>)
.values
.map(
(e) => e["category_name"].toString(),
)
.toList(),
),
);
});
}
final urlShops =
'https://jhola-e90ff.firebaseio.com/registeredShops/grocery.json';
var responseShops = await http.get(urlShops);
print(responseShops.body);
final List<NamesItem> loadedShops = [];
var extractedShops =
json.decode(responseShops.body) as Map<String, dynamic>;
// print(extractedShops);
if (extractedShops != null) {
extractedShops.forEach((shopId, shopData) {
// List<DealItem> loadedDeals = [];
loadedShops.add(
NamesItem(
id: shopId.toString(),
name: shopData['name'].toString(),
description: shopData['address'].toString(),
status: shopData["loggedIn"].toString(),
namesLat: shopData['lat'].toString(),
namesLong: shopData['long'].toString(),
address: shopData['address'].toString(),
contact: shopData['phone'].toString(),
menu: shopData["items"] == null
? []
: (shopData["items"] as Map<String, dynamic>)
.values
.map((e) => MenuItem(
id: e["productId"].toString(),
name: e["productName"].toString(),
price: double.parse(e["productPrice"].toString()),
description: e["productDescription"].toString(),
stock: e["stock"].toString(),
image:
"https://firebasestorage.googleapis.com/v0/b/jhola-e90ff.appspot.com/o/images%2F${e['productId'].toString()}?alt=media&token=37e96ab0-172d-4387-88a5-18c508abe70b",
))
.toList(),
deal: shopData["deals"] == null
? []
: (shopData["deals"] as Map<String, dynamic>)
.values
.map((e) => DealItem(
id: e["productId"].toString(),
name: e["productName"].toString(),
price: double.parse(e["productPrice"].toString()),
description: e["productDescription"].toString(),
stock: e['stock'].toString(),
image:
"https://firebasestorage.googleapis.com/v0/b/jhola-e90ff.appspot.com/o/images%2F${e['productId'].toString()}?alt=media&token=37e96ab0-172d-4387-88a5-18c508abe70b"))
.toList(),
),
);
});
}
print("helooooooooo");
_restaurantNames = loadedRestaurant.toList();
_restaurantNames.forEach((element) {
print(element.name);
});
_shopNames = loadedShops.toList();
}
}