Question

I’m playing around with an idea(never played with TypeDescriptors before), and managed to get it to work nicely. But I’m concerned about some “best practice” decisions I made during my little experiment.

I use a CustomTypeDescriptor, that receives an event from its PropertyDescriptors indicating that the values are changing or being queried.

The TypeDescriptorProvider generates a completely new instance of CustomTypeDescriptor every time GetTypeDescriptor is called, it then binds the events on the CustomTypeDescriptor to the instance object.

I’m unsure whether or not generating a new CustomTypeDescriptor each time GetTypeDescriptor is called would be a good idea(even though I had to, to get this to work). I’m also unsure if there are any consequences with binding events directly from the CustomTypeDescriptor to the instance object, especially if the CustomTypeDescriptor is dynamic.

What do you guys think? Sample code of my Provider below:

Class EntityTypeDescriptionProvider
    Inherits TypeDescriptionProvider

Public Sub New(ByVal parent As TypeDescriptionProvider)
    MyBase.New(parent)
End Sub
Protected Sub New()

End Sub

Public Overrides Function GetTypeDescriptor(ByVal objectType As Type, ByVal instance As Object) As ICustomTypeDescriptor
    Dim _CustomTypeDescriptor As EntityTypeDescriptor

    'Grabbin the base descriptor.
    Dim Descriptor As ICustomTypeDescriptor = MyBase.GetTypeDescriptor(objectType, Nothing)

    'If for...whatever reason the instance is empty, return the default descriptor for the type.
    If instance Is Nothing Then
        Return Descriptor
    End If

    'If the instance doesnt implement the interface I use for Descriptor customization
    '(which should never happen) return the default descriptor for the type.
    If Not Functions.IsImplemented(instance.GetType, GetType(ICustomTypeDescriptorEntity)) Then
        Return Descriptor
    End If

    '
    '
    'some lengthy "customization" based on the state of the instance.
    '
    '

    AddHandler _CustomTypeDescriptor.GetValue, AddressOf CType(instance, ICustomTypeDescriptorEntity).GetValue
    AddHandler _CustomTypeDescriptor.SetValue, AddressOf CType(instance, ICustomTypeDescriptorEntity).SetValue

    Return _CustomTypeDescriptor
End Function
End Class

Answer 1

I’ve been using this for a while and it hasnt blown up at all.

Feedback still welcome, I’m answering this to lay it to rest.