If else语句在Flutter中未显示正确的输出。

huangapple
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英文:

If else statement not showing proper output in Flutter

问题

我已经将代码部分翻译好，以下是翻译好的部分：

我正在跟随YouTube上的课程视频设计Flutter中的购物车。但根据课程视频，我应该看到输出显示商品的图片、价格、单位和其他细节[如图1所示]。但在我的输出中，我只看到了AppBar标题[如图2所示]。


`YouTube课程视频中的输出：`

[![示例][1]][1]


`我的输出：`

[![我的输出][2]][2]


我已经附上了整个代码，希望能帮助我找出错误。
英文:

I am following a course video from YouTube to design a shopping cart in Flutter. But according to the course video, I am supposed to see the output showing the pictures of the items, their prices, units, and other details [shown in picture 1]. But in my output I am seeing nothing but only the AppBar title [shown in picture 2].

The output in the YouTube course video:

If else语句在Flutter中未显示正确的输出。

My Output:

If else语句在Flutter中未显示正确的输出。

I have attached the entire code below, please help fix my mistake.

main.dart

import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'package:shopping_cart/cart_provider.dart';
import 'package:shopping_cart/cart_screen.dart';
import 'package:shopping_cart/product_list.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return ChangeNotifierProvider(
      create: (_) => CartProvider(),
      child: Builder(builder: (BuildContext context) {
        return MaterialApp(
          title: 'Flutter Demo',
          theme: ThemeData(),
          debugShowCheckedModeBanner: false,
          home: const CartScreen(),
        );
      }),
    );
  }
}

product_list.dart

import 'package:badges/badges.dart';
import 'package:flutter/material.dart' hide Badge;
import 'package:provider/provider.dart';
import 'package:shopping_cart/cart_model.dart';
import 'package:shopping_cart/db_helper.dart';
import 'cart_provider.dart';
import 'cart_screen.dart';
class ProductListScreen extends StatefulWidget {
const ProductListScreen({super.key});
@override
State<ProductListScreen> createState() => _ProductListScreenState();
}
class _ProductListScreenState extends State<ProductListScreen> {
DBHelper? dbHelper = DBHelper();
List<String> productName = [
'Mango',
'Orange',
'Grapes',
'Banana',
'Chery',
'Peach',
'Mixed Fruit Basket'
];
List<String> productUnit = [
'KG',
'Dozen',
'KG',
'Dozen',
'KG',
'KG',
'KG',
];
List<int> productPrice = [10, 20, 30, 40, 50, 60, 70];
List<String> productImage = [
'https://image.shutterstock.com/image-photo/mango-isolated-on-white-background-600w-610892249.jpg',
'https://image.shutterstock.com/image-photo/orange-fruit-slices-leaves-isolated-600w-1386912362.jpg',
'https://image.shutterstock.com/image-photo/green-grape-leaves-isolated-on-600w-533487490.jpg',
'https://media.istockphoto.com/photos/banana-picture-id1184345169?s=612x612',
'https://media.istockphoto.com/photos/cherry-trio-with-stem-and-leaf-picture-id157428769?s=612x612',
'https://media.istockphoto.com/photos/single-whole-peach-fruit-with-leaf-and-slice-isolated-on-white-picture-id1151868959?s=612x612',
'https://media.istockphoto.com/photos/fruit-background-picture-id529664572?s=612x612',
];
@override
Widget build(BuildContext context) {
final cart = Provider.of<CartProvider>(context); // reference
return Scaffold(
appBar: AppBar(
title: const Text("Product List"),
centerTitle: true,
backgroundColor: Colors.deepPurple,
actions: [
InkWell(
onTap: () {
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => CartScreen(),
),
);
},
child: Center(
child: Badge(
badgeContent: Consumer<CartProvider>(
builder: (context, value, child) {
return Text(
value.getCounter().toString(),
style: const TextStyle(
color: Colors.white,
fontSize: 15,
fontWeight: FontWeight.bold,
),
);
},
),
badgeAnimation: const BadgeAnimation.fade(
animationDuration: Duration(milliseconds: 300),
),
child: const Icon(
Icons.shopping_cart_outlined,
size: 30,
),
),
),
),
const SizedBox(width: 20),
],
),
body: Column(
children: [
Expanded(
child: ListView.builder(
itemCount: productName.length,
itemBuilder: ((context, index) {
return Card(
child: Padding(
padding: const EdgeInsets.all(12.0),
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.start,
children: [
Row(
mainAxisAlignment: MainAxisAlignment.start,
crossAxisAlignment: CrossAxisAlignment.center,
mainAxisSize: MainAxisSize.max,
children: [
Image(
height: 100,
width: 100,
image:
NetworkImage(productImage[index].toString()),
),
const SizedBox(
width: 15,
),
Expanded(
child: Column(
mainAxisAlignment: MainAxisAlignment.start,
crossAxisAlignment: CrossAxisAlignment.start,
children: [
Text(
productName[index],
style: const TextStyle(fontSize: 23),
),
const SizedBox(
height: 5,
),
Text(
productUnit[index] +
" " r"$" +
productPrice[index].toString(),
style: const TextStyle(fontSize: 23),
),
const SizedBox(
height: 10,
),
Align(
alignment: Alignment.centerRight,
child: InkWell(
onTap: () {
dbHelper!
.insert(Cart(
id: index,
productId: index.toString(),
productName: productName[index]
.toString(),
initialPrice:
productPrice[index],
productPrice:
productPrice[index],
quantity: 1,
unitTag: productUnit[index]
.toString(),
image: productImage[index]
.toString()))
.then((value) {
print("Product is Added to Cart");
cart.addTotalPrice(double.parse(
productPrice[index].toString()));
cart.addCounter();
}).onError((error, stackTrace) {
print(error.toString());
});
},
child: Container(
height: 35,
width: 130,
decoration: BoxDecoration(
borderRadius:
BorderRadius.circular(50),
color: Colors.green,
),
child: const Center(
child: Text(
"Add to Cart",
style: TextStyle(
color: Colors.white,
fontSize: 20,
fontWeight: FontWeight.w500),
),
),
),
),
)
],
),
)
],
)
],
),
),
);
}),
),
),
Consumer<CartProvider>(builder: (context, value, child) {
return Column(
children: [
ReusableWidget(
'subtotal',
r'$' + value.getTotalPrice().toStringAsFixed(2),
),
],
);
})
],
),
);
}
}
class ReusableWidget extends StatelessWidget {
final String title, value;
const ReusableWidget(this.title, this.value, {super.key});
@override
Widget build(BuildContext context) {
return Padding(
padding: const EdgeInsets.symmetric(vertical: 4),
child: Row(
children: [
Text(
title,
style: Theme.of(context).textTheme.titleSmall,
),
Text(
value,
style: Theme.of(context).textTheme.titleSmall,
)
],
),
);
}
}

db_helper.dart

import 'package:sqflite/sqflite.dart';
import 'package:path_provider/path_provider.dart';
import 'package:path/path.dart';
import 'dart:io' as io;
import 'cart_model.dart';
class DBHelper {
static Database? _db;
Future<Database?> get db async {
_db = await initDatabase();
if (_db != null) {
return _db!;
}
}
initDatabase() async {
io.Directory documentDirectory = await getApplicationDocumentsDirectory();
String path = join(documentDirectory.path, 'cart.db');
var db = await openDatabase(path, version: 1, onCreate: _onCreate);
return db;
}
// Method
_onCreate(Database db, int version) async {
await db.execute(
'CREATE TABLE cart (id INTEGER PRIMARY KEY, productId VARCHAR UNIQUE, productName TEXT, initialPrice INTEGER, productPrice INTEGER, quantity INTEGER, unitTag TEXT, image TEXT)',
);
}
Future<Cart> insert(Cart cart) async {
print(cart.toMap());
var dbClient = await db;
await dbClient!.insert('cart', cart.toMap());
return cart;
}
Future<List<Cart>> getCartList() async {
var dbClient = await db;
final List<Map<String, Object?>> queryResult =
await dbClient!.query("cart");
return queryResult.map((e) => Cart.fromMap(e)).toList();
}
}

cart_screen.dart

import 'package:badges/badges.dart';
import 'package:flutter/material.dart' hide Badge;
import 'package:provider/provider.dart';
import 'cart_model.dart';
import 'cart_provider.dart';
class CartScreen extends StatefulWidget {
const CartScreen({super.key});
@override
State<CartScreen> createState() => _CartScreenState();
}
class _CartScreenState extends State<CartScreen> {
@override
Widget build(BuildContext context) {
final cart = Provider.of<CartProvider>(context);
return Scaffold(
appBar: AppBar(
title: const Text("My Products"),
centerTitle: true,
backgroundColor: Colors.deepPurple,
actions: [
Center(
child: Badge(
badgeContent: Consumer<CartProvider>(
builder: (context, value, child) {
return Text(
value.getCounter().toString(),
style: const TextStyle(
color: Colors.white,
fontSize: 15,
fontWeight: FontWeight.bold,
),
);
},
),
badgeAnimation: const BadgeAnimation.fade(
animationDuration: Duration(milliseconds: 300),
),
child: const Icon(
Icons.shopping_cart_outlined,
size: 30,
),
),
),
const SizedBox(width: 20),
],
),
body: Column(
children: [
FutureBuilder(
future: cart.getData(),
builder: (context, AsyncSnapshot<List<Cart>> snapshot) {
if (snapshot.hasData) {
return Expanded(
child: ListView.builder(
itemCount: snapshot.data!.length,
itemBuilder: ((context, index) {
return Card(
child: Padding(
padding: const EdgeInsets.all(12.0),
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.start,
children: [
Row(
mainAxisAlignment: MainAxisAlignment.start,
crossAxisAlignment: CrossAxisAlignment.center,
mainAxisSize: MainAxisSize.max,
children: [
Image(
height: 100,
width: 100,
image: NetworkImage(
snapshot.data![index].image.toString(),
),
),
const SizedBox(
width: 15,
),
Expanded(
child: Column(
mainAxisAlignment:
MainAxisAlignment.start,
crossAxisAlignment:
CrossAxisAlignment.start,
children: [
Text(
snapshot.data![index].productName
.toString(),
),
const SizedBox(
height: 5,
),
Text(
snapshot.data![index].unitTag
.toString() +
" " r"$" +
snapshot.data![index].productPrice
.toString(),
style: const TextStyle(fontSize: 23),
),
const SizedBox(
height: 10,
),
Align(
alignment: Alignment.centerRight,
child: InkWell(
onTap: () {},
child: Container(
height: 35,
width: 130,
decoration: BoxDecoration(
borderRadius:
BorderRadius.circular(50),
color: Colors.green,
),
child: const Center(
child: Text(
"Add to Cart",
style: TextStyle(
color: Colors.white,
fontSize: 20,
fontWeight:
FontWeight.w500),
),
),
),
),
)
],
),
)
],
)
],
),
),
);
}),
),
);
} else {
return const Text("Shahzain");
}
},
)
],
),
);
}
}

cart_provider.dart

import 'package:flutter/material.dart';
import 'package:shared_preferences/shared_preferences.dart';
import 'package:shopping_cart/cart_model.dart';
import 'package:shopping_cart/db_helper.dart';
class CartProvider with ChangeNotifier {
DBHelper db = DBHelper(); // DBHelper() is a class
int _counter = 0;
int get counter => _counter;
double _totalPrice = 0.0;
double get totalPrice => _totalPrice;
late Future<List<Cart>> _cart;
Future<List<Cart>> get cart => _cart; // => means to indicate
Future<List<Cart>> getData() async {
_cart = db.getCartList();
return _cart;
}
void _setPrefItems() async {
SharedPreferences prefs = await SharedPreferences.getInstance();
prefs.setInt('cart_item', _counter);
prefs.setDouble('total_price', _totalPrice);
notifyListeners();
}
void _getPrefItems() async {
SharedPreferences prefs = await SharedPreferences.getInstance();
// giving initial value by ?? 0 for null safety
_counter = prefs.getInt('cart_item') ?? 0;
// giving initial value by ?? 0.0 for null safety
_totalPrice = prefs.getDouble('total_price') ?? 0.0;
notifyListeners();
}
void addTotalPrice(double productPrice) {
_totalPrice = _totalPrice + productPrice;
_setPrefItems();
notifyListeners();
}
void removeTotalPrice(double productPrice) {
_totalPrice = _totalPrice - productPrice;
_setPrefItems();
notifyListeners();
}
double getTotalPrice() {
_getPrefItems();
return _totalPrice;
}
void addCounter() {
// initial value of counter was 0, will be incremented to 1, and will be stored to sharedPreferences
_counter++;
_setPrefItems();
notifyListeners();
}
void removeCounter() {
_counter--;
_setPrefItems();
notifyListeners();
}
int getCounter() {
_getPrefItems();
return _counter;
}
}

cart_model.dart

class Cart {
late final int? id;
final String? productId;
final String? productName;
final int? initialPrice;
final int? productPrice;
final int? quantity;
final String? unitTag;
final String? image;
// Creating the constructor
Cart({
required this.id, // primary key
required this.productId,
required this.productName,
required this.initialPrice,
required this.productPrice, 
required this.quantity,
required this.unitTag,
required this.image,
});
Cart.fromMap(Map<dynamic, dynamic> res) // res = resources
: id = res['id'], 
productId = res['productId'],
productName = res['productName'],
initialPrice = res['initialPrice'],
productPrice = res['productPrice'],
quantity = res['quantity'],
unitTag = res['unitTag'],
image = res['image'];
Map<String, Object?> toMap(){
return  {
'id' : id,
'productId' : productId,
'productName' : productName,
'initialPrice' : initialPrice,
'productPrice' : productPrice,
'quantity' : quantity,
'unitTag' : unitTag,
'image' : image
};
}
}

答案1

得分: 2

在你的 main.dart 文件中，你设置了：

home: const CartScreen(),

而在你所跟随的视频教程中，他设置了 home: ProductListsScreen()。

请修正这个问题，希望你的问题会得到解决。

此外，请确保在何处使用 const。

英文:

in your main.dart file

you set,

home: const CartScreen(),

and the video tutorial you have followed, he sets home: ProductListsScreen()

Fix this and I hope your problem will be solved,

also, be sure where to use const

huangapple
  • 本文由 发表于 2023年2月9日 02:04:21
  • 转载请务必保留本文链接：https://go.coder-hub.com/75389961.html
  • android
  • dart
  • database
  • flutter
  • if-statement
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