Make a generic instance giveh the type (not instance)

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I have a generic class used to serialise an event to/from a name-value pairs dictionary. It has the following class signature:-

VB

Public Class EventSerializer(Of TEvent As {New, IEvent})

It has a factory method that can create it from an instance of the class thus:-

VB

    Public Function Create(Of TEvent As {New, IEvent})(ByVal evt As TEvent) As EventSerializer(Of TEvent)
        Return Create(Of TEvent)()
    End Function

    Public Function Create(Of TEvent As {New, IEvent})() As EventSerializer(Of TEvent)
' creation happens here
    End Function

How would I go about making a factory method that could create the serializer if a System.Type parameter is passed in :-

VB

Public Function Create(ByVal evtType As System.Type) As EventSerializer(Of ?)

?

What I have tried:

Instantiating the type by reflection works but is not elegant nor really correct..

Posted 22-Oct-17 6:52am

Duncan Edwards Jones

Updated 24-Oct-17 9:11am

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Richard Deeming · Accepted Answer · 2017-10-24T09:10:00

You'd need a non-generic base class or interface containing the members of your class which don't rely on the generic type parameter.

VB.NET

Public MustInherit Class EventSerializer
    ' Non-generic members here...
    
    Public Shared Function Create(Of TEvent As {New, IEvent})(ByVal evt As TEvent) As EventSerializer(Of TEvent)
        Return Create(Of TEvent)()
    End Function
    
    Public Shared Function Create(Of TEvent As {New, IEvent})() As EventSerializer(Of TEvent)
        ' Magic happens here...
    End Function
    
    Public Shared Function Create(ByVal evtType As Type) As EventSerializer
        Dim method As MethodInfo = GetType(EventSerializer).GetMethod("Create", BindingFlags.Public Or BindingFlags.Static, Nothing, Type.EmptyTypes, Nothing)
        Dim result As Object = method.MakeGenericMethod(evtType).Invoke(Nothing, Nothing)
        Return DirectCast(result, EventSerializer)
    End Function
End Class

Public Class EventSerializer(Of TEvent As {New, IEvent})
    Inherits EventSerializer
    
    ' Generic members here...
End Class

You might want to cache the MethodInfo for the generic method in a shared field, to avoid the overhead of finding it each time you call the non-generic factory method.