Nested Classes (after much hair pulling)

[Ray Cassick]

Ok, I want to create an object hierarchy within my application that will take care of holding some common settings as an alternative to using global vars. I also want this to be a holding area for the application level configuration info that will be read in from a few XML configuration files. My intent is to serialize this data to an XML file latter and pass the file onto some external plug in type components so they can parse through it as they need to and grab what ever configuration settings they need. The basic gist of what I am looking for is this.... I want to have a parent class (App) to contain a few nested classes (Paths, Config, etc...), and each of these nested classes to have some properties internal to them. My intent here is to be able to create one instance of the parent class and get access to all the members of the child classes as so:

App.Paths.Path1
...
App.Config.Setting1
...

Now, what I wanted (expected to be able to do) was:

Class App

Public Paths as CPaths
Public Config as CConfig

Public sub New()
    Paths = new CPaths
    Config = new CConfig

End sub

Protected Class CPaths

    Private \_Path1 as string

    Protected sub New()
    ...
    Protected Readonly Property Path1 as String
        Get
            Return \_Path1
        End Get
    End Property

End Class

Protected Class CConfig

    Private \_Setting1 as string

    Protected sub New()
    ...
    Protected Readonly Property Setting1 as String
        Get
            Return \_Setting1
        End Get
    End Property

End Class

End Class

Instead what I HAD to do was make each one of the nested classes public because I could not declare a public instance of a protected nested class in the parent class constructor!!! While this does appear to work, it also seems to allow a developer to bypass my parent class and directly create instances of my nested classes. IE They can instansiate the public members of the class directly like so:

Dim objAppPaths As New App.CPaths

This really seems to be counter productive to building this hierarchy in the first place. Am I missing something here?

[Richard Deeming]

Make the nested classes and their properties Public, but make the constructors as Friend. That way, only code within your assembly can create instances of the internal class. You may be better off using Shared methods instead, which would remove the need to create instances of the class. For example:

Class App
Public Class Paths
Private Shared _Path1 as String
Shared Sub New()
'Initialize your properties here
End Sub
Private Sub New()
'No need to create instances of this class
End Sub

    Public Shared Readonly Property Path1 As String
        Get
            Return \_Path1
        End Get
    End Property
End Class

Public Class Config
    Private Shared \_Setting1 As String
    Shared Sub New()
        'Initialize your properties here
    End Sub
    Private Sub New()
        'No need to create instances of this class
    End Sub

    Public Shared Readonly Property Setting1 As String
        Get
            Return \_Setting1
        End Get
    End Property
End Class

Shared Sub New()
    'Initialize any properties for App here
End Sub
Private Sub New()
    'No need to create instances of this class
End Sub

End Class

Then, you can just use:

Dim Path1 As String = App.Paths.Path1

Updated: the member variables have to be Shared as well! :-O