The simple example below works find. However if I change the 'Access Level' of the properties in the Box class to 'Protected Friend' which I figured would work as well, it errors with "Public member 'Height' on type 'Box' not found."

If I then change the definition of myBox and myCreate to:

Dim myBox As Box
Dim myCreate As Crate

myBox = new Box
myCreate = new Create

It works.

I cant see why changing the Access Level caused a problem and why I had to change the definition of my instances of the objects? Any comments please?





Module Module1

    Sub Main()
        Dim myBox = New Box
        Dim myCreate = New Crate


        'myBox = New Box
        'myCreate = New Crate

        myBox.Height = 5.0
        myBox.Width = 6.0
        myBox.Depth = 7.0

        myCreate.height = 2.5
        myCreate.width = 3.5
        myCreate.depth = 4.5

        Console.WriteLine(" Volume of myBox: {0}", myBox.volume())
        Console.WriteLine(" Volume of myCreate: {0}", myCreate.Volume())
        Console.ReadLine()


    End Sub

    Public Class Box
        Public Height As Double
        Public Width As Double
        Public Depth As Double

        Public Sub New()

            Height = 0.0
            Width = 0.0
            Depth = 0.0

        End Sub

        Public Function Volume() As Double

            Return Height * Width * Depth

        End Function

    End Class

    Public Class Crate
        Inherits Box

        Public Quantity As Integer

        Public Sub New()

            Height = 0.0
            Width = 0.0
            Depth = 0.0
            Quantity = 0

        End Sub

    End Class
End Module

I would also expect "Protected Friend" to behave the same as "Public" in this case as you are deriving Crate from Box. However, I very seldom use public class fields like this when building classes. I always go with the "private field, public accessor" approach. Perhaps the compiler has an issue with Protected class fields (i.e. a public Integer) vs a public/protected property that exposes a private class field.

-Peter