vb.net Serializing Collections unable to add a collection to object? - json

Question

I'm trying to generate some JSON that looks like this:
{
"#type": "MessageCard",
"sections": [
{
"activityTitle": " Request",
"facts": [
{
"name": "name1",
"value": "Value"
},
{
"name": " Date:",
"value": "Value Date"
}
],
"text": "Some Test."
}
],
"potentialAction": [
{
"#type": "ActionCard",
"name": "Add a comment",
"inputs": [
{
"#type": "TextInput",
"id": "comment",
"isMultiline": true
}
]
}
]
}
I performed a paste special into VS and it generated the class structure for me as such:
Public Class MessageCard
Public Property type As String
Public Property context As String
Public Property summary As String
Public Property themeColor As String
Public Property sections() As Section
Public Property potentialAction() As Potentialaction
End Class
I'm trying to add the sections to the object as such:
Dim m as New MessageCard
Dim s As New List(Of Section)
s.Add(s1)
s.Add(s2)
m.sections = s
The compiler complains that it cannot convert a list of Sections into a Section. Did the class get generated incorrectly, or am i constructing it incorrectly?

Answer 1

First, your JSON is not quite complete and the Classes you show wont create that JSON.
As posted, that JSON simply shows a Sections and potentialAction class which are not related in any way. An enclosing [ ... ] is needed to represent the MessageCard class containing the two of them.
[{
"#type": "MessageCard",
...
}]
Next, the class you have shows all sorts of things not present in the JSON: context, summary and themeColor for instance. I assume those might be missing for brevity, but it is confusing. There is also 2 other Types missing which are in the JSON, Fact and Input.
Corrected, the classes should be:
Public Class MsgCard
<JsonProperty("#type")>
Public Property ItemType As String
Public Property sections As List(Of Section)
Public Property potentialAction As List(Of Potentialaction)
Public Sub New()
sections = New List(Of Section)
potentialAction = New List(Of Potentialaction)
End Sub
End Class
Public Class Section
Public Property activityTitle As String
Public Property facts As Fact()
Public Property text As String
End Class
Public Class Fact
Public Property name As String
Public Property value As String
End Class
Public Class Potentialaction
<JsonProperty("#type")>
Public Property ActionType As String
Public Property name As String
Public Property inputs As Input()
End Class
Public Class Input
<JsonProperty("#type")>
Public Property InputType As String
Public Property id As String
Public Property isMultiline As Boolean
End Class
Notes
You did not specify a JSON serializer, so this is prepared to JSON.NET as recommended by Microsoft.
#type is an illegal property name, so the JsonProperty attribute is used to create an alias. I also used less confusingly redundant names.
You may want to change Fact and Input to List(Of T) if you will be creating and pushing them into the class object as well.
Finally, for the actual question you asked, most of the automatic class generators have trouble with arrays (even VS).
Public Property sections() As Section
' should be:
Public Property sections As Section()
That simply declares that sections will be an array, it does not create the array. Normally this is not a problem because the Serializer/Deserializer will create the array. To allow code external to the class to add to them, you probably want to use a List as the classes above do, then create the instance in the constructor:
Public Sub New()
sections = New List(Of Section)
potentialAction = New List(Of Potentialaction)
End Sub