Question

I am developing a custom user control. The user control has a property that maps to an enumeration and should not have any default value, i.e. the consumer of the control MUST set it.

The property:

<Description("This is the property description"),
Category("SomeCategory"), Bindable(True)>
Public Property SomeProperty As Enumerations.SomeEnumeration?

The enumeration:

Namespace Enumerations
    Public Enum SomeEnumeration
        Zero = 0
        One
        Two
    End Enum
End Namespace

The check:

If SomeProperty Is Nothing Then
    Throw New ApplicationException("You must set SomeProperty.")
End If

The problem:

All of the logic works. My problem is that none of the enumeration values show up in intellisense when you try to set SomeProperty from markup. A colleague of mine found this related support request, so it appears to be a known issue.

My question is, what is the best way to support all of the behaviors I need on this control, as well as keep intellisense on this property?

Answer 1

I could recreate this issue – making an enumeration nullable makes the intellisense stop working. I guess this is because nullable types are objects.

Suggest keeping the enumeration as NOT nullable. Have a default value of NotSet or None. If the enumeration is not set, you could throw an exception in your getter or initialization code.

Property

<Description("This is the property description"),
Category("SomeCategory"), Bindable(True)>
Public Property SomeProperty As Enumerations.SomeEnumeration

Enumeration

Namespace Enumerations
    Public Enum SomeEnumeration
        NotSet = -1
        Zero = 0
        One
        Two
    End Enum
End Namespace

Check

If SomeProperty Is SomeProperty.NotSet Then
    Throw New ApplicationException("You must set SomeProperty.")
End If