ClaraU ClaraU - 2 months ago 16
C# Question

Newtonsoft JSON - How to use the JsonConverter.ReadJson method to convert types when deserializing JSON

I need help understanding how to use the the JsonConverter.ReadJson method to convert a value of any number of types (string, boolean, Date, int, array, object) to a specific custom type.

For example, I have the following;

public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
//where reader.Value could be a string, boolean, Date, int, array, object
//and in this example the value of reader.Value is a string
return new MyCustomType(reader.Value);
}


But this gives error;

Compilation error (line 115, col 36): Argument 1: cannot convert from 'object' to 'string'


I'm a bit green with C#, just need help making this work.

Answer

Finally worked it out;

public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
    MyCustomType myCustomType = new MyCustomType();//for null values        

    if (reader.TokenType != JsonToken.Null)
    {           
        if (reader.TokenType == JsonToken.StartArray)
        {
            JToken token = JToken.Load(reader); 
            List<string> items = token.ToObject<List<string>>();  
            myCustomType = new MyCustomType(items);
        }
        else
        {
            JValue jValue = new JValue(reader.Value);
            switch (reader.TokenType.ToString())
            {
                case "String":
                    myCustomType = new MyCustomType((string)jValue);
                    break;
                case "Date":
                    myCustomType = new MyCustomType((DateTime)jValue);
                    break;
                case "Boolean":
                    myCustomType = new MyCustomType((bool)jValue);
                    break;
                case "Integer":
                    int i = (int)jValue;
                    myCustomType = new MyCustomType(i);
                    break;
                default:
                    Console.WriteLine("Default case");
                    Console.WriteLine(reader.TokenType.ToString());
                    break;
            }
        }
    }      
    return myCustomType;
}

Not sure if this is the best possible solution, but it does the job.