I'm developing an app that manages glossary food items. I can't figure out what is the mistake I've done. Here's my code...

First, I've created a class called 'Product' that contains all the required fields like Product name, Product Image, item Type and quantity etc

The model :

class Product {
  String id;
  final String productName;
  final String itemType;
  final String productImage;
  final String purchasedDate;
  final String expiryDate;
  final String quantity;

  Product({
    this.id = '',
    required this.productName,
    required this.productImage,
    required this.itemType,
    required this.purchasedDate,
    required this.expiryDate,
    required this.quantity,
  });

  Map<String, dynamic> toJson() => {
        'id': id,
        'ProductImage': productImage,
        'ProductName': productName,
        'PurchasedDate': purchasedDate,
        'ExpiryDate': expiryDate,
        'ItemType': itemType,
        'Quantity': quantity,
      };

  static Product fromJson(Map<String, dynamic> json) => Product(
      productName: json['ProductName'],
      productImage: json['productImage'],
      itemType: json['ItemType'],
      purchasedDate: json['purchasedDate'],
      expiryDate: json['ExpiryDate'],
      quantity: json['Quantity']);
}

The code for implementation :

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:expire_x/utils/product.dart';
import 'package:flutter/material.dart';

class HomePageTwo extends StatefulWidget {
  const HomePageTwo({Key? key}) : super(key: key);

  @override
  State<HomePageTwo> createState() => _HomePageTwoState();
}

class _HomePageTwoState extends State<HomePageTwo> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("home page"),
      ),
      body: StreamBuilder<List<Product>>(
        stream: readProduct(),
        builder: (context, snapshot) {
          if (snapshot.hasError) {
            return Text("Something went wrong> ${snapshot.error}");
          } else if (snapshot.hasData) {
            final product = snapshot.data!;
            return ListView(
              children: product.map(buildProduct).toList(),
            );
          } else {
            return Center(
              child: CircularProgressIndicator(),
            );
          }
        },
      ),
    );
  }

  Widget buildProduct(Product product) => ListTile(
        title: Text(product.productName),
      );

  Stream<List<Product>> readProduct() => FirebaseFirestore.instance
      .collection('Products')
      .snapshots()
      .map((snapshot) =>
          snapshot.docs.map((doc) => Product.fromJson(doc.data())).toList());

  Future CreateProduct() async {
    final docProduct = FirebaseFirestore.instance.collection('Products').doc();

    final product = Product(
      id: docProduct.id,
      productImage: 'ddd',
      productName: "productName",
      purchasedDate: "purchasedDate",
      expiryDate: "expiryDate",
      itemType: "itemType",
      quantity: "quantity",
    );
    final json = product.toJson();
    await docProduct.set(json);
  }
}

The json response from firebase that I wanted : json response

And the error :

type 'Null' is not a subtype of type 'String'

In the emulator

I'm new to flutter. Can anyone please help me?

CodePudding user response：

This error occurs when you add required keyword in the constructor. And one of the value appears to be null.

To overcome this

• Make sure that all the fields in all the documents is filled.

OR

• Avoid using required use null operator instead ? if you are not sure the documents to be filled everytime.

Like:

class Product {
  String? id;
  String? productName;
  String? itemType;
  String? productImage;
  String? purchasedDate;
  String? expiryDate;
  String? quantity;

  Product({
    this.id = '',
    this.productName,
    this.productImage,
    this.itemType,
    this.purchasedDate,
    this.expiryDate,
    this.quantity,
  });

CodePudding user response：

Typo mistake in your model class

static Product fromJson(Map<String, dynamic> json) => Product(
  productName: json['ProductName'],
  productImage: json['ProductImage'],       // It should be 'ProductImage'
  itemType: json['ItemType'],
  purchasedDate: json['PurchasedDate'],    // and this should be 'PurchasedDate'
  expiryDate: json['ExpiryDate'],
  quantity: json['Quantity']);