声明“可空<string> []" 或 "string[]?" 对于 class 中可能存在也可能不存在的字符串数组属性？</string>

Question

I have a JSON file like this:

[
  {
    "Id": 1,
    "Size": "big",
    "Order": 6
  },
  {
    "Id": 2,
    "Size": "small",
    "Order": 4
  },
  {
    "Id": 3,
    "Size": "medium",
    "Order": 2,
    "chips": []
  }
]

The chips property is an array that may or may not appear in some object (It is currently null at this point). Should I declare the class for the json file like this:

 public class Settings
    { 
        public int Id { get;}
        public string Size { get;}
        public int Order { get;}
        public string[]? Chips { get;}
    }

with the? or something like Nullable[] for the property instead?

Answer 1

In short: you don't need Nullable<T> or ? in this case at all.

string[] is reference type:

Console.WriteLine(typeof(string[]).IsValueType);

the printed output will be false .

So, it can be null without any decoration.

---

Back to your sample. You need to specify setters as well to be able deserialize the given json fragement:

public class Settings
{
    public int Id { get; set; }
    public string Size { get; set; }
    public int Order { get; set; }
    public string[] Chips { get; set; }
}

Because the top-level entity is not an object that's why you need to use JArray to parse it first and then convert it to Settings via the ToObject ( 1 ):

var json = "[\r\n  {\r\n    \"Id\": 1,\r\n    \"Size\": \"big\",\r\n    \"Order\": 6\r\n  },\r\n  {\r\n    \"Id\": 2,\r\n    \"Size\": \"small\",\r\n    \"Order\": 4\r\n  },\r\n  {\r\n    \"Id\": 3,\r\n    \"Size\": \"medium\",\r\n    \"Order\": 2,\r\n    \"chips\": []\r\n  }\r\n]";
var semiParsedData = JArray.Parse(json);
var settings = semiParsedData.ToObject<Settings[]>();