I was working on a section of this code that is grabbing api data. In it I'm taking the json file and reading to a string into json.net to deserialize and put parts of the data into an object class. The way the json reads is a list of Result objects. I have gotten the count from the root method but I am having problems getting data from the list of Result objects.

Object classes

    public class Result
{
    
    public string id { get; set; }
    
    public string status { get; set; }
}

public class WarehouseInformation
{

    public int count { get; set; }
    public List<Result> result { get; set; }
}

orderData is the string of the json file being read in.

    {
        Console.WriteLine("orderdatatoarray");


        WarehouseInformation warehouseInformation = JsonConvert.DeserializeObject<WarehouseInformation>(orderData);


        if (warehouseInformation != null)
        {
            var test = warehouseInformation.count;
            string[] orderStringArr = new string[0];
            
            Console.WriteLine(test);

            List<Result> idList = new List<Result>();




            return orderStringArr;
        }
        else
        {
            string[] orderStringArr = new string[0];
            return orderStringArr;
        }

        
    }
}

The error is: System.NullReferenceException: 'Object reference not set to an instance of an object.'

last is part of the json file I am trying to read from, I doubt this is the issue at fault but I might have missed a way to setup the classes above. json api structure

CodePudding user response：

In Newtonsoft, model binding will take place under 2 circumstances

1. the member name matches the json key exactly as it is written
2. the member name is different, but is annotated with [JsonProperty("jsonKeyNameHere")] to specify the exact json field it must bind to

As such in the WarehouseInformation class it should be either

1. public List<Result> results { get; set; }
2. [JsonProperty("results")] public List<Result> result { get; set; }

Using either is fine, personally I prefer #2 as it allows you to name your members in line with C# naming practices, and the compiler won't throw you a million warnings because the naming is non-standard. A bit more work, but it makes for clean code. But if that doesn't matter or you prefer you members mimic the json keys 1:1, then route #1 is perfectly fine.

In NewtonSoft, json structure dictates the composition patterns of the classes. So this is what you have right now: if WarehouseInformation is seen as a container for the entire Json response, then you are grabbing the "count" field and the "results" json array (which translates to a List), and for each element of "results", you are taking "id" and "status". This composition pattern is right, its just you need the naming to line up for proper model binding

CodePudding user response：

not sure if this your issue but you named the class to deserialize "result" instead of "results"