我无法从Firestore Flutter检索和查看数据

Question

#HOME：这是链接到FeatureProducts((的主页

并且我无法检索数据"；产品"；，它总是返回零。

我想将Firebase中的数据检索到Listview中。

这是我的firebase云火库firebase数据库的图像

我用很多方法尝试了很多次，所有的代码都没有给出任何错误，但当我运行应用程序并打开活动时，数据无法显示它们将是空的，

import 'package:farmers_ecommerce/commons/common.dart';
import 'package:farmers_ecommerce/db/product.dart';
import 'package:farmers_ecommerce/pages/product_search.dart';
import 'package:farmers_ecommerce/provider/product.dart';
import 'package:farmers_ecommerce/provider/user_provider.dart';
import 'package:farmers_ecommerce/widget/featured_products.dart';
import 'package:farmers_ecommerce/widget/product_card.dart';
import 'package:farmers_ecommerce/widgets/custom_text.dart';
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'cart.dart';
import 'order.dart';
class HomePage extends StatefulWidget {
@override
_HomePageState createState() => _HomePageState();
}
class _HomePageState extends State<HomePage> {
final _key = GlobalKey<ScaffoldState>();
ProductServices _productServices = ProductServices();

@override
Widget build(BuildContext context) {
final userProvider = Provider.of<UserProvider>(context);
final productProvider = Provider.of<ProductProvider>(context);
return Scaffold(
key: _key,
backgroundColor: Colors.white,
endDrawer: Drawer(
child: ListView(
children: <Widget>[
UserAccountsDrawerHeader(
decoration: BoxDecoration(color: Colors.black),
accountName: CustomText(
text: userProvider.userModel?.name ?? "username lading...",
color: Colors.white,
weight: FontWeight.bold,
size: 18,
),
accountEmail: CustomText(
text: userProvider.userModel?.email ?? "email loading...",
color: Colors.white,
),
),
ListTile(
onTap: () async{
await userProvider.getOrders();
changeScreen(context, OrdersScreen());
},
leading: Icon(Icons.bookmark_border),
title: CustomText(text: "My orders"),
),
ListTile(
onTap: () async{
userProvider.signOut();
},
leading: Icon(Icons.exit_to_app),
title: CustomText(text: "Log out"),
),
],
),
),
body: SafeArea(
child: ListView(
children: <Widget>[
//         Custom App bar
Stack(
children: <Widget>[
Positioned(
top: 10,
right: 20,
child: Align(
alignment: Alignment.topRight,
child: GestureDetector(
onTap: () {
_key.currentState.openEndDrawer();
},
child: Icon(Icons.menu))),
),
Positioned(
top: 10,
right: 60,
child: Align(
alignment: Alignment.topRight,
child: GestureDetector(
onTap: (){
changeScreen(context, CartScreen());
},
child: Icon(Icons.shopping_cart))),
),
Positioned(
top: 10,
right: 100,
child: Align(
alignment: Alignment.topRight, child: GestureDetector(
onTap: (){
_key.currentState.showSnackBar(SnackBar(
content: Text("User profile")));
},
child: Icon(Icons.person))),
),
Padding(
padding: const EdgeInsets.all(8.0),
child: Text(
'What arenyou Shopping for?',
style: TextStyle(
fontSize: 30,
color: Colors.black.withOpacity(0.6),
fontWeight: FontWeight.w400),
),
),
],
),
//          Search Text field
//            Search(),
Container(
decoration: BoxDecoration(
color: Colors.white,
borderRadius: BorderRadius.only(
bottomRight: Radius.circular(20),
bottomLeft: Radius.circular(20))),
child: Padding(
padding: const EdgeInsets.only(
top: 8, left: 8, right: 8, bottom: 10),
child: Container(
decoration: BoxDecoration(
color: Colors.grey.withOpacity(0.2),
borderRadius: BorderRadius.circular(20),
),
child: ListTile(
leading: Icon(
Icons.search,
color: Colors.black,
),
title: TextField(
textInputAction: TextInputAction.search,
onSubmitted: (pattern)async{
await productProvider.search(productName: pattern);
changeScreen(context, ProductSearchScreen());
},
decoration: InputDecoration(
hintText: "fashion....",
border: InputBorder.none,
),
),
),
),
),
),
//            featured products
Row(
children: <Widget>[
Padding(
padding: const EdgeInsets.all(14.0),
child: Container(
alignment: Alignment.centerLeft,
child: new Text('Featured products')),
),
],
),
FeaturedProducts(), 
**this is the feature products. i cannot see any thing on here. 
its blank**
//          recent products
Row(
children: <Widget>[
Padding(
padding: const EdgeInsets.all(14.0),
child: Container(
alignment: Alignment.centerLeft,
child: new Text('Recent products')),
),
],
),
Column(
children: productProvider.products
.map((item) => GestureDetector(
child: ProductCard(
product: item,
),
))
.toList(),
)
],
),
),
);
}
}

#FEATURED PRODUCT：这链接到ProductProvider，它从数据库

import 'package:farmers_ecommerce/provider/product.dart';
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'featured_card.dart';
class FeaturedProducts extends StatefulWidget {
@override
_FeaturedProductsState createState() => _FeaturedProductsState();
}
class _FeaturedProductsState extends State<FeaturedProducts> {
@override
Widget build(BuildContext context) {
final productProvider = Provider.of<ProductProvider>(context);
return Container(
height: 230,
child: ListView.builder(
scrollDirection: Axis.horizontal,
itemCount: productProvider.products.length,
itemBuilder: (_, index) {
return FeaturedCard(
product: productProvider.products[index],
);
}));
}
}

#PRODUCT PROVIDER//我觉得提供商没有加载任何产品

import 'package:farmers_ecommerce/db/product.dart';
import 'package:farmers_ecommerce/models/product.dart';
import 'package:flutter/material.dart';
class ProductProvider with ChangeNotifier{
ProductServices _productServices = ProductServices();
List<ProductModel> products = [];
List<ProductModel> productsSearched = [];

ProductProvider.initialize(){
loadProducts();
}
loadProducts()async{enter code here
products = await _productServices.getProducts();
notifyListeners();
}
Future search({String productName})async{
productsSearched = await _productServices.searchProducts(productName: productName);
notifyListeners();
}
}

//DATABASE TO FIRESTORE//我尝试使用流生成器，但使用Future不起作用。

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:farmers_ecommerce/models/product.dart';

class ProductServices {
String collection = "products";
FirebaseFirestore _firestore = FirebaseFirestore.instance;
Future<List<ProductModel>> getProducts() async =>
_firestore.collection(collection).get().then((result) {
List<ProductModel> products = [];
for (DocumentSnapshot product in result.docs) {
products.add(ProductModel.fromSnapshot(product));
}
return products;
});
Future<List<ProductModel>> searchProducts({String productName}) {
// code to convert the first character to uppercase
String searchKey = productName[0].toUpperCase() + productName.substring(1);
return _firestore
.collection(collection).  //return fire base
.orderBy("name")
.startAt([searchKey])
.endAt([searchKey + 'uf8ff'])
.get()
.then((result) {
List<ProductModel> products = [];
for (DocumentSnapshot product in result.docs) {
products.add(ProductModel.fromSnapshot(product));
}
return products;
});
}
}

Answer 1

在ProductServices中更改此函数：

Future<List<ProductModel>> getProducts() async {
QuerySnapshot result= await _firestore.collection(collection).get();
List<ProductModel> products = [];
for (DocumentSnapshot product in result.docs) {
products.add(ProductModel.fromSnapshot(product));
}
return products;
}

如果使用then，则当代码流已经离开函数时，将调用return。为了避免这种情况，您需要await结果。