Problems deserializing JSON data in VB.NET

Question

I am attempting to deserialize a simple JSON array to .NET objects using the JSON.NET library in visual basic.

For the life of me, I cannot figure out what I am doing wrong here. My JSON string deserializes into appropriate objects (9 in total), but none of the properties are populated.

My code:

Public Class result

  Public Property id As Integer

  Public Property vote_percentage As String

  Public Sub New()

  End Sub

  Public Sub New(ByVal id As Integer, ByVal vote_percentage As String)
    Me.id = id
    Me.vote_percentage = vote_percentage
  End Sub

End Class

The JSON data I am trying to deserialize looks like this:

[{"finalist":{"id":12,"vote_percentage":"28"}},{"finalist":{"id":13,"vote_percentage":"6"}},{"finalist":{"id":14,"vote_percentage":"4"}},{"finalist":{"id":15,"vote_percentage":"3"}},{"finalist":{"id":16,"vote_percentage":"7"}},{"finalist":{"id":17,"vote_percentage":"1"}},{"finalist":{"id":18,"vote_percentage":"47"}},{"finalist":{"id":19,"vote_percentage":"2"}},{"finalist":{"id":20,"vote_percentage":"1"}}]

Finally my deserialization:

Dim Results As New List(Of result)

Results = JsonConvert.DeserializeObject(Of List(Of result))(_result)

The result is 9 objects that don't have any property values assigned.

I am racking my brain, so if someone could throw me a bone I would appreciate it.

Thanks.

UPDATE:

So here is the change I made that got this to work:

Modified my result class to contain a property finalist of type finalist

Created a new class finalist with properties id and vote_percentage

Public Class finalist

    Public Property id As Integer

    Public Property vote_percentage As String

    Public Sub New()

    End Sub

    Public Sub New(ByVal id As Integer, ByVal vote_percentage As String)
        Me.id = id
        Me.vote_percentage = vote_percentage
    End Sub
End Class

Public Class result

    Public Property finalist As finalist

    Public Sub New()
        finalist = New finalist
    End Sub

    Public Sub New(ByVal id As Integer, ByVal vote_percentage As String)
        Me.finalist = New finalist(id, vote_percentage)
    End Sub

End Class

Left the deserialization alone:

_result = System.Text.Encoding.ASCII.GetString(data)

Dim Results As New List(Of result)

Results = JsonConvert.DeserializeObject(Of List(Of result))(_result)

RaiseEvent VoteCompleted(loopCounter, _VoteCount, time, _result)

And it works.

A note for new people (like myself). When using JSON.NET you have to have constructor methods (i.e. Sub New) in order for the properties to get set during the Deserialization call.

Could you try parsing the json without the wrapped finalist property? Currently you have an array of objects with only a finalist property, which your class does not have. — pimvdb
– pimvdb, Commented Feb 3, 2012 at 17:56
I don't understand what you mean. Are you suggesting I remove all instances of the finalist from the json string? I was under the impression that the finalist mapped to a single instance of a result class. — jdbenn
– jdbenn, Commented Feb 3, 2012 at 18:11
pimvdb - you got me onto something and it fixed it. I updated my code to show a working solution. — jdbenn
– jdbenn, Commented Feb 3, 2012 at 18:16
this seems relavent: stackoverflow.com/questions/2272111/… — Zach Green
– Zach Green, Commented Feb 3, 2012 at 18:20
@jdbenn: Could you please copy your solution to an answer and mark it accepted (yes, you can answer you own question and accept your own answer)? That way the question will show up as answered. — John M Gant
– John M Gant, Commented Feb 3, 2012 at 20:59

pimvdb · Accepted Answer · 2012-02-03 20:50:10Z

I don't know JSON.NET but I can tell that you have an array of objects which have a different structure than your VB.NET class defines.

You can see this more clearly if you format your JSON:

[
  {
    "finalist": {
      "id": 12,
      "vote_percentage": "28"
    }
  },

  {
    "finalist": {
      "id": 13,
      "vote_percentage": "6"
    }
  },

  ...
]

I guess (as I have very little knowledge of the .NET platform) that JSON.NET requires a list of instances of a class with the same structure - so a class definition like this (pseudocode):

class item
    public property finalist as result

class result
    public property id as Integer
    public property vote_percentage as String

What you might also want to do is simply get rid of the item class and use result objects directly like this in your JSON:

[
  {
    "id": 12,
    "vote_percentage": "28"
  },

  {
    "id": 13,
    "vote_percentage": "6"
  },

  ...
]

That way, you have a simplified array of objects representing result instances, without seemingly useless "wrapper objects" (i.e. those representing item instances).

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