Class to JSON VB.Net - json

Question

So I have a class which I am serializing to Json. All goes well, until this nested class, which gives me an System.NullReferenceException = {"Object reference not set to an instance of an object."}. When writing the code, intelisense recognizes the nested class, but obviously I'm missing a declaration somewhere.
Root class:
Public Class RootObject
Private _metadata As List(Of Metadata)
Public Property metadata() As List(Of Metadata)
Get
Return _metadata
End Get
Set(ByVal value As List(Of Metadata))
_metadata = value
End Set
End Property
Private _test_gl As List(Of TestGl)
Public Property test_gl() As List(Of TestGl)
Get
Return _test_gl
End Get
Set(ByVal value As List(Of TestGl))
_test_gl = value
End Set
End Property
End Class
Here is the TestGl class definition:
Public Class TestGl
Private _ref_key_3 As String
<JsonProperty("ref-key-3")> _
Public Property ref_key_3() As String
Get
Return _ref_key_3
End Get
Set(ByVal value As String)
_ref_key_3 = value
End Set
End Property
Private _currency_amount As CurrencyAmount
<JsonProperty("currency-amount")> _
Public Property currency_amount() As CurrencyAmount
Get
Return _currency_amount
End Get
Set(ByVal value As CurrencyAmount)
_currency_amount = value
End Set
End Property
End Class
And finally the CurrencyAmount class:
Public Class CurrencyAmount
Private _currency As String
<JsonProperty("currency")> _
Public Property currency() As String
Get
Return _currency
End Get
Set(ByVal value As String)
_currency = value
End Set
End Property
Private _amount As String
<JsonProperty("amount")> _
Public Property amount() As String
Get
Return _amount
End Get
Set(ByVal value As String)
_amount = value
End Set
End Property
End Class
Here follow the code of filling up the object with data:
Dim Root As RootObject
Dim Meta_Data As New List(Of Metadata)()
Dim Test_Gl As New List(Of TestGl)()
Root = New RootObject
Root.metadata = New List(Of Metadata)()
Root.test_gl = New List(Of TestGl)
Meta_Data = Root.metadata
Test_Gl = Root.test_gl
And here I assign values to it:
Test_Gl.Add(New AccountGl)
Test_Gl(ItemNo).ref_key_3 = "test"
Test_Gl(ItemNo).currency_amount.currency = "EUR"
Test_Gl(ItemNo).currency_amount.amount = "100"
The line where currency_amount.currency gets assigned, it goes wrong and I'm looking at it for several hours already. I don't see it.
Any input would be highly appreciated.
The properties are written in full as I need to work on this project in VS2008.

Answer 1

I suspect somewhere you need to initialize _currency_amount to a new instance of CurrencyAmount I don't see new CurrencyAmount anywhere.
I suspect that you don't really want to allow the currency_amount property to be set, otherwise you should have set it in your sample assignment code at the bottom. If this is the case, then you probably shouldn't even have a Set member defined for TestGl (it should be ReadOnly, which affects only currency_amount and not _currency_amount.currency). Instead you should create a default instance of CurrencyAmount and assign it to that field during the construction of TestGl. That could be as simple as changing your declaration of _currency_amount to:
Private _currency_amount As New CurrencyAmount
Alternatively, and this may be the solution you need to use with a JSON serializable object, you keep the Set member definition, and just add a line to your test code to initialize currency_amount before using it:
Test_Gl(ItemNo).currency_amount = new CurrencyAmount