在vb.net中转换自定义类以接受变量类型

Question

I am fairly new to custom classes in VB.Net and am having a bit of an issue with assigning a value from my class to the class object. See code below:

Public Class NType
    Public Const Small As Double = 1
    Public Const Medium As Double = 2
    Public Const Large As Double = 3

'Another thing I tried...
    Public Shared ReadOnly Property _Small As Double
        Get
            Return Small
        End Get
    End Property
End Class

However as soon as I do:

Dim NType1 as NType = NType.Small

I get an error to say Value of type 'Double' cannot be converted to 'Harris.NType'

I assume there will be some sort of way to allow this (in a similar vein to how, say Color works)

Answer 1

I think that, from the looks of it, what you actually want is an enumeration rather than a class.

Public Enum NType

    Small
    Medium
    Large

End Enum

Dim nType1 As NType = NType.Small

You can specify the actual values but, generally, those values should be irrelevant and all that matters is that they're unique and don't change. By default, an enumeration is stored as an Integer but you can specify any integral type. By default, the first value is equal to zero and each subsequent value is equal to 1 more than the previous one. You can specify one or more values if you need to though.

Public Enum NType As Short

    Small = 1
    Medium
    Large

End Enum

The values still increment by 1 but will now start at 1 instead of zero. You should only do that if you will be using the same numeric values to represent the same data elsewhere and the two must match. Don't do it just because you can.