“null”類型不是“map string dynamic”類型的子類型 flutter

Question

我正在嘗試在我的應用程序中使用 API 它可以正常工作，但是當 JSON 獲取 null 時，該應用程序無法正常工作。

正常工作：

{
   "product":{
      "description_1":"Lorem Ipsum is simply dummy text of the printing and typesetting industry.",
      "description_2":"Contrary to popular belief, Lorem Ipsum is not simply random text. It has roots in a piece of classical Latin literature from 45 BC, making it over 2000 years old.",
      "description_3":"There are many variations of passages of Lorem Ipsum available, but the majority have suffered alteratenter code hereion in some form",
      "description_4":"The standard chunk of Lorem Ipsum used since the 1500s is reproduced below for those interested.",
      "description_5":"Various versions have evolved over the years, sometimes by accident, sometimes on purpose (injected humour and the like"
   }
}

錯誤：“類型‘null’不是‘映射字符串動態’類型的子類型”：

{ “產品”：null }

Class：

class Store {
  Store({
    required this.product,
  });

  Product product;

  factory Store.fromJson(Map<String, dynamic> json) => Store(
        product: Product.fromJson(json["product"]),
      );

  Map<String, dynamic> toJson() => {
        "product": product.toJson(),
      };
}

class Product {
  Product({
    required this.description1,
    required this.description2,
    required this.description3,
  });

  String description1;
  String description2;
  String description3;

  factory Product.fromJson(Map<String, dynamic> json) => Product(
        description1: json["description_1"] ?? "",
        description2: json["description_2"] ?? "",
        description3: json["description_3"] ?? "",
      );

  Map<String, dynamic> toJson() => {
        "description_1": description1,
        "description_2": description2,
        "description_3": description3,
      };
}

Answer 1

如果產品實際上可以是null那么Store需要處理它。 將Store class product屬性更改為可以為空? 像下面這樣的符號：

class Store {
  Store({
    this.product,
  });

  Product? product;

  factory Store.fromJson(Map<String, dynamic> json) => Store(
        product: json["product"] != null 
            ? Product.fromJson(json["product"])
            : null,
      );

  Map<String, dynamic> toJson() => {
        "product": product?.toJson(),
      };
}