Deserialize object does not return full data in Xamarin.Forms

Question

I have a JSON object that is coming back based on the keyword that the user type. It is returning only some of the typed keyword from the user. When I check postman and type the same keyword it returns properly.

The following exception is raised:

Newtonsoft.Json.JsonSerializationException: 
Must specify valid information for parsing in the string

JSON

{
  "valid": true,
  "result": {
    "points": [
      {
        "pointId": "505",
        "name": "Building one",
        "description": "Office of Technology and Data Application Development",
        "latitude": "xxx",
        "longitude": "xxx",
        "floor": "B",
        "aliases": [],
        "comments": [],
        "images": []
      }
    ],
    "categories": []
  },
  "errors": []
}

Model classes

public class SearchPoints
{
    public bool Valid { get; set; }
    public Result Result { get; set; }
    public List<string> Errors { get; set; }
}

public class Result
{
    public List<Point> Points { get; set; }
    public List<Category> Categories { get; set; }
}

public class Category
{
  public long CategoryId { get; set; }
  public string Name { get; set; }
  public long ParentId { get; set; }
  public string Parent { get; set; }
}

public class Point
{
    public long PointId { get; set; }
    public string Name { get; set; }
    public string Description { get; set; }
    public string Latitude { get; set; }
    public string Longitude { get; set; }
    public Floor Floor { get; set; }
    public List<string> Aliases { get; set; }
    public List<string> Comments { get; set; }
    public List<string> Images { get; set; }
}

public enum Floor 
{ 
    A, 
    B 
};

Service method

var apiResponse = await _httpClient.GetAsync(Url + _keyword);
var apiContent = apiResponse.Content.ReadAsStringAsync().Result;
var pointsJsonResponse = JsonConvert.DeserializeObject<SearchPoints>(apiContent);

var potentialPoints = new ObservableCollection<Point>(pointsJsonResponse.Result.Points);

PointsItemSource = potentialPoints;

Answer 1

The JSON shown in your question deserializes successfully into the data model shown in your question, see https://dotnetfiddle.net/nDhNPL.

The exception shown in your question, however, provides some information. The (somewhat opaque) message Must specify valid information for parsing in the string only appears only once in the Json.NET sources, according to a search, specifically in EnumUtils.ParseEnum(Type enumType, NamingStrategy? namingStrategy, string value, bool disallowNumber):

public static object ParseEnum(Type enumType, NamingStrategy? namingStrategy, string value, bool disallowNumber)
{

// SNIP

    if (firstNonWhitespaceIndex == -1)
    {
        throw new ArgumentException("Must specify valid information for parsing in the string.");
    }

The relevant code is throwing an exception if, when parsing an enum string, the incoming value contains only whitespace. So I modified the JSON in your question as follows:

    "floor": " ",

And reproduced the exception as shown here: https://dotnetfiddle.net/6zaG9W.

Thus you must actually be attempting to parse JSON with an empty or whitespace value for Floor and failing because this is not possible. To make this work, you could:

1. Change Point.Floor to be a string:

   public string Floor { get; set; }
   

   The JSON will now parse successfully. Demo fiddle here: https://dotnetfiddle.net/zg5YWr.

2. Use a special subclass of StringEnumConverter that handles empty strings for Floor. One example is shown in the answer to How to handle deserialization of empty string into enum in json.net by Davor Zlotrg, which I generalize here:

   public class EmptyTolerantStringEnumConverter : StringEnumConverter
   {
       public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
       {
           if (reader.TokenType == JsonToken.String && string.IsNullOrWhiteSpace(reader.Value.ToString()))
               // Return a default value.  Note if deserializing a nullable enum the default value is null
               return Activator.CreateInstance(objectType);
   
           return base.ReadJson(reader, objectType, existingValue, serializer);
       }       
   }
   

   And apply it as follows:

   [JsonConverter(typeof(EmptyTolerantStringEnumConverter))]
   public Floor Floor { get; set; }
   

   Or, if you prefer to map "" to a nullable:

   [JsonConverter(typeof(EmptyTolerantStringEnumConverter))]
   public Floor? Floor { get; set; }
   

   Demo fiddle here: https://dotnetfiddle.net/DwGKHU

Related: How to tell Json.Net globally to apply the StringEnumConverter to all enums and parsing an enumeration in JSON.net.

Answer 2

I'm pretty sure Json.Net cannot deserialize an 'object' type. It needs the real type:

So replace all your List<object> with List<TRealType>.

Example:

    public List<string> Aliases { get; set; }
    public List<string> Comments { get; set; }
    public List<string> Images { get; set; }

If you still get the error, then the error is in your apiContent variable which would not be a proper json string.

You also need to put the [JsonConverter(typeof(StringEnumConverter))] attribute on your enum type.