未處理的例外：型別“List<dynamic>”不是“List<imageObject>”型別的子型別？|如何在顫動的模型firebase中輸入物件陣列

我一直在嘗試從firebase實際獲取資料所以實際資料是：

如何獲取 imageUrl ？

我的嘗試是：

class ProductModel {
  String? name;
  String? price;
  String? discountPrice;
  String? discountRate;
  String? category;
  String? description;
  List<imageObject>? image;

  ProductModel(
      {required this.name,
      required this.price,
      this.category,
      this.description,
      this.discountPrice,
      this.discountRate,
      this.image});

  ProductModel.fromMap(Map<String, dynamic> data) {
    
    name = data['name'];
    // image = data['imageUrls'][0]['url']; // To get single image i do this
    image = data['imageUrls']; // but this is not working 
    category = data['category'];
    description = data['Description'];
    price = data['price'];
    discountPrice = data['discountPrice'];
    discountRate = data['discountRate'];
  }
}

class imageObject {
  final String public_id;
  final String url;

  imageObject({
    required this.public_id,
    required this.url,
  });
}

它給出了例外：Unhandled Exception: type 'List<dynamic>' is not a subtype of type 'List<imageObject>?'

并訪問我正在做的第一張圖片，

product.image![0].url,

其中產品的型別是 ProductModel

但這不起作用

uj5u.com熱心網友回復：

您還需要反序列化imageObject json 資料。為此，您需要將工廠 imageObject.fromJson()建構式添加到您的imageObject類，就像您為 ProductModel 類所做的那樣。

這是您需要的代碼：

  class ProductModel {
  String? name;
  String? price;
  String? discountPrice;
  String? discountRate;
  String? category;
  String? description;
  List<imageObject>? image;

  ProductModel({
    required this.name,
    required this.price,
    this.category,
    this.description,
    this.discountPrice,
    this.discountRate,
    this.image,
  });

  factory ProductModel.fromJson(Map<String, dynamic> jsonData) => ProductModel(
        name: jsonData['name'] as String?,
        price: jsonData['price'] as String?,
        category: jsonData['category'] as String?,
        description: jsonData['Description'] as String?,
        discountPrice: jsonData['discountPrice'] as String?,
        discountRate: jsonData['discountRate'] as String?,
        
        //Have a good look here to understand how nested list of maps are deserialized

        image: (jsonData['imageUrls'] as List<dynamic>?)
            ?.map((e) => imageObject.fromJson(e as Map<String, dynamic>))
            .toList(),
      );
}

class imageObject {
  final String public_id;
  final String url;

  imageObject({
    required this.public_id,
    required this.url,
  });

  factory imageObject.fromJson(Map<String, dynamic> jsonData) => imageObject(
        public_id: jsonData['public_id'] as String,
        url: jsonData['url'] as String,
      );
}

我們在這里所做的是，將 imageUrls 鍵中的資料作為 List 并通過 imageObject 方法的 json 建構式映射每個單獨的元素。

uj5u.com熱心網友回復：

您必須將接收串列映射到imageObjects 串列。

1. imageObject為你的類創建一個 fromMap 建構式

class imageObject {
  final String public_id;
  final String url;

  imageObject({
    required this.public_id,
    required this.url,
  });
  imageObject.fromMap(Map<String, dynamic> map) => imageObject(public_id = map['public_id'], url = map['url'] );
}

2. 像下面這樣使用它：

 ProductModel.fromMap(Map<String, dynamic> data) {
    
    name = data['name'];
    image = data['imageUrls'].map((map) => imageObject.fromMap(map) ); 
    category = data['category'];
    description = data['Description'];
    price = data['price'];
    discountPrice = data['discountPrice'];
    discountRate = data['discountRate'];
  }

您可能需要添加一些轉換或對以前的代碼進行一些修改以使其作業，但這是一般的想法。

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