How to deserialize a List(Of Object) from JSON? - json

Question

I have a List(Of Object) that I am using in a property of type IEnumerable(Of Object). I can serialize it fine but cannot work out then how to deserialize it from JSON back to a List(Of Object). Any help would be really great please.
My ViewModel:
Public Class ViewModel
Inherits ViewModelBase
Public Class MapSettings
<Display(Name:="Map Name", Description:="Enter a optional name for the map.", GroupName:="Map Settings")>
Public Property MapName As String
<Display(Name:="Map Description", Description:="Enter a optional description for the map.", GroupName:="Map Settings")>
Public Property MapDescription As String
<Display(Name:="Map Comments", Description:="Enter optional comments for the map.", GroupName:="Map Settings")>
Public Property MapComments As String
<Display(Name:="Map Version", Description:="Enter a optional version for the map.", GroupName:="Map Settings")>
Public Property MapVersion As String
End Class
Public Class GeneralSettings
<Display(Name:="Route Colour", Description:="Sets the colour of the routes design line on the map.", GroupName:="General Settings")>
Public Property Foreground As Color
End Class
Private _myItems() As IEnumerable(Of Object)
Public Property MyItems() As IEnumerable(Of Object)
Get
If _myItems Is Nothing Then
Return New List(Of Object)() From {
New MapSettings,
New GeneralSettings With {.Foreground = Colors.Blue}
}
Else
Return _myItems
End If
End Get
Set(value As IEnumerable(Of Object))
_myItems = value
OnPropertyChanged()
End Set
End Property
End Class
My serialize code that I cannot complete:
Dim MyItems_New = JsonConvert.DeserializeObject(Of MyItems???)(MyJsonString)
JSON:
{
"MyItems": [
{
"MapName": null,
"MapDescription": null,
"MapComments": null,
"MapVersion": null
},
{
"Foreground": "#FF0000FF"
}
]
}

Answer 1

I just found that Newtonsoft has built-in support for type handling, which can be enabled by setting the JsonSerializerSettings.TypeNameHandling property and passing it to the serialization methods. As long as you control the input, this should let you both serialize and deserialize your list without a problem.
Serialize:
Dim myItems = JsonConvert.SerializeObject(myVM.MyItems, Formatting.None, New JsonSerializerSettings() With { .TypeNameHandling = TypeNameHandling.Auto })
Deserialize:
Dim myItems_New = JsonConvert.DeserializeObject(Of List(Of Object))(MyJsonString, New JsonSerializerSettings() With { .TypeNameHandling = TypeNameHandling.Auto })
In your question, MyJsonString appears to be a serialized version of your ViewModel class rather than just the list itself. If this is the case, change DeserializeObject(Of List(Of Object)) to DeserializeObject(Of ViewModel).
Resulting JSON:
[
{
"$type": "MapSettings, YourProjectNamespace",
"MapName": "New York",
"MapDescription": "Map over New York",
"MapComments": null,
"MapVersion": "v1"
},
{
"$type": "GeneralSettings, YourProjectNamespace",
"Foreground": "#FF0000"
}
]
Try it online (C#):
https://dotnetfiddle.net/0jCIGL
However, if these two classes are all you are planning to use this list for, then you'd be better off using something along the lines of Jimi's proposed solution, as then you're always working with strongly-typed objects.