How to deserialize json

Here is a Converter Helper class (converted from C#) used in commercial applications. It will convert to/From POCOs <-> JSON.

Imports Newtonsoft.Json

Public Class JsonConverter
    Public Shared Function FromClass(Of T)(data As T, Optional isEmptyToNull As Boolean = False, Optional jsonSettings As JsonSerializerSettings = Nothing) As String
        Dim response As String = String.Empty

        If (data IsNot Nothing) Then
            Try ' try..catch only required during debugging
                response = JsonConvert.SerializeObject(data, jsonSettings)
            Catch ex As Exception
                Debug.WriteLine(ex)
                Throw
            End Try
        End If
        Return If(isEmptyToNull, (If(response = "{}", "null", response)), response)
    End Function

    Public Shared Function ToClass(Of T)(data As String, Optional jsonSettings As JsonSerializerSettings = Nothing) As T
        Dim response As T = Nothing

        If Not String.IsNullOrEmpty(data) Then
            Try ' try..catch only required during debugging
                response = If(jsonSettings Is Nothing, JsonConvert.DeserializeObject(Of T)(data), JsonConvert.DeserializeObject(Of T)(data, jsonSettings))
            Catch ex As Exception
                Debug.WriteLine(ex)
                Throw
            End Try
        End If
        Return response
    End Function
End Class

To Use it:

Dim raw As New Data() With
{
    .Codice = "Field 1",
    .Descrizione = "Field 2",
    .Composizione = "Field 3",
    .CodCategoria = "Field 4"
}

Dim json As String = JsonConverter.FromClass(raw)
Dim raw2 = JsonConverter.ToClass(Of Data)(json)

UPDATE

I must admit, I did not look closely at the JSON data until I looked at Richard's Solution.

So the following update uses the above JsonConverter helper class but also maintains the class structure that you want. The only thing that you need to do is add the custom ResultDataConverter attribute to the Result class.

Imports System.IO
Imports Newtonsoft.Json.Linq
Imports Json = Newtonsoft.Json

Module Module1

    Sub Main()

        Dim filePath As String = Path.Combine("FilePath", "FileName")
        Dim data As String = FileHelper.TextRead(filePath)

        Dim result = JsonConverter.ToClass(Of Result)(data)
        Debugger.Break()

    End Sub

End Module

<Json.JsonConverter(GetType(ResultDataConverter))>
Public Class Result
    Public Property Data() As List(Of Data)
End Class

Public Class Data
    Public Property CODICE() As String
    Public Property DESCRIZIONE() As String
    Public Property COMPOSIZIONE() As String
    Public Property CODCATEGORIA() As String
    Public Property PREZZO() As Single
    Public Property PREZZOPROMO() As Single
    Public Property SCONTOPROMO() As Single
    Public Property PROMODADATA() As Date
    Public Property PROMOADATA() As Date
    Public Property CODMODELLO() As String
    Public Property DESCRIZIONEBREVEWEB() As String
End Class

Public Class ResultDataConverter
    Inherits Json.JsonConverter
    Public Overrides Function CanConvert(objectType As Type) As Boolean
        Return True
    End Function

    Public Overrides Function ReadJson(reader As Json.JsonReader, objectType As Type, existingValue As Object, serializer As Json.JsonSerializer) As Object
        Dim obj As Result = Nothing
        If reader.TokenType = Json.JsonToken.StartObject Then
            Dim jObject As JObject = JObject.Load(reader)
            If jObject IsNot Nothing AndAlso jObject.HasValues Then
                Dim result = jObject("result")
                If result IsNot Nothing Then
                    obj = New Result()
                    Dim root = serializer.Deserialize(Of IList(Of JObject))(result.CreateReader())
                    Dim jMeta = root.First().Children().Where(Function(x) x.Path = "meta")
                    Dim jData = root.First().Children().Where(Function(x) x.Path = "data")
                    Dim lookup = jMeta.Children() _
                                      .Children() _
                                      .Select(Function(x) x.First.ToString()) _
                                      .Select(Function(x, i) New With {.x = x, .i = i}) _
                                      .ToDictionary(Function(x) x.x, Function(x) x.i)
                    Dim dataElements = jData.Children().Children().ToList()
                    obj.Data = New List(Of Data)()
                    For i As Integer = 0 To dataElements.Count - 1
                        Dim element = New Data()
                        If lookup.Keys.Contains("CODICE") Then
                            element.CODICE = dataElements(i)(lookup("CODICE")).ToString()
                        End If
                        If lookup.Keys.Contains("DESCRIZIONE") Then
                            element.DESCRIZIONE = dataElements(i)(lookup("DESCRIZIONE")).ToString()
                        End If
                        ' do the same for all other data properties
                        obj.Data.Add(element)
                    Next
                End If
            End If
        End If
        Return obj
    End Function

    Public Overrides Sub WriteJson(writer As Json.JsonWriter, value As Object, serializer As Json.JsonSerializer)
        Throw New NotImplementedException()
    End Sub
End Class

Public Class FileHelper
    Public Shared Function TextRead(fileName As String) As String
        Return TextRead(Path.GetFileName(fileName), Path.GetDirectoryName(fileName))
    End Function

    Public Shared Function TextRead(fileName As String, filePath As String) As String
        Dim data As String = String.Empty
        Dim myFile As String = Path.Combine(filePath, fileName)

        If Directory.Exists(filePath) AndAlso File.Exists(myFile) Then
            Using reader = New StreamReader(myFile)
                data = reader.ReadToEnd()
            End Using
        End If
        Return data
    End Function
End Class

By encapsulating the property mapping in a custom converter, this will make it easier in future to update if the JSON meta fields change. Simply update the Data class properties, then adjust the mappings in the custom converter.

Note: The custom ResultDataConverter is incomplete. You will need to add the other properties where I left a comment and bullet-proof the conversion if there is incomplete JSON data.