Nested Class - Prevent Instantiation of Nested Class

[devonknows]

Hi All,

Just a query really as i havent really written a class from scratch before so i am struggling getting my head round the log of it to be honest.

What: I am trying to extend a class with another class, so once the main class has been instantiated then they can then choose from a series of subclasses that they can they populate properties - the final peice will have approx 150 properties so i need to break up and catagorise some properties.

My issue here is that when i created a nested class, the user can directly instantiate the subclass which i do not want them to do, i want all the subclasses to be part of the main class and prevent direct instantiation of them.

This is what i want them to do:

        Dim IE1 As New IncomeExpenditure
        IE1.CustomerData.FullName = "HELLO"

I do not want them to be able to do this.

Dim IE2 As New IncomeExpenditure.CustomerInfo
        IE2.FullName = "Test"

Here is my class code so far, can someone please help me code out the ability to directly instantiate the sub class becuase there will be subs/functions in the main class that accesses properties through the sub class so i do not want them accessing it as this class will be a widely used class in several applications (once built). I have read items on Inherit, Private Default Constructors etc but when i make the change it gives me errors about accessing private members on the classes etc or the 'CustomerData' becomes unavailable.

Appreciate any help you guys can give.

Public Class IncomeExpenditure
    Public CustomerData As CustomerInfo



    'Private
    Private m_TimeStampID As String
    Private m_ActiveStatus As String
    Private m_SourceId As String
    Private EmployeeId As Integer

    Public Sub New()
        'Private Constructor
        Debug.Print("Constructor")

    End Sub

#Region "Customer Info Class"
    '##############################################################
    'Class: clsHouseHoldInfo
    'Values:    Under 14 Dependent Children
    '           14 - 16 Dependant Children (19 if in further ed)
    '           Non Dependent Household Members (Bill Contributers)
    '##############################################################
    Public Class CustomerInfo
        Private m_AC_ACCOUNT_NUMBER As Long
        Private m_AC_ACCOUNT_NAME As String
        Private m_AC_ACCOUNT_DOB As Date
        Private m_AC_ACCOUNT_EMAIL As Date

        Public Property DebtId() As Long
            Get
                Return m_AC_ACCOUNT_NUMBER
            End Get
            Set(value As Long)
                m_AC_ACCOUNT_NUMBER = value
            End Set
        End Property
        Public Property FullName() As String
            Get
                Return m_AC_ACCOUNT_NAME
            End Get
            Set(value As String)
                m_AC_ACCOUNT_NAME = value
            End Set
        End Property
        Public Property DateOfBirth() As Date
            Get
                Return m_AC_ACCOUNT_DOB
            End Get
            Set(value As Date)
                m_AC_ACCOUNT_DOB = value
            End Set
        End Property
        Public Property EmailAddress() As Date
            Get
                Return m_AC_ACCOUNT_DOB
            End Get
            Set(value As Date)
                m_AC_ACCOUNT_DOB = value
            End Set
        End Property
    End Class
#End Region

#Region "HouseHold Info Class"
    '##############################################################
    'Class: clsHouseHoldInfo
    'Values:    Under 14 Dependent Children
    '           14 - 16 Dependant Children (19 if in further ed)
    '           Non Dependent Household Members (Bill Contributers)
    '##############################################################
    Private Class clsHouseHoldInfo
        Private m_AC_DEPENDENT_CHILDREN_LT14 As Long
        Private m_AC_DEPENDENT_CHILDREN_14PL As Long
        Private m_AC_NO_IN_HOUSEHOLD As Long
        Private m_AC_VEHICLES_IN_HOUSEHOLD As Long

        Public Property Under14_Dependants() As Long
            Get
                Return m_AC_DEPENDENT_CHILDREN_LT14
            End Get
            Set(value As Long)
                m_AC_DEPENDENT_CHILDREN_LT14 = value
            End Set
        End Property
        Public Property Over14_Dependants() As Long
            Get
                Return m_AC_DEPENDENT_CHILDREN_14PL
            End Get
            Set(value As Long)
                m_AC_DEPENDENT_CHILDREN_14PL = value
            End Set
        End Property
        Public Property NonDependants() As Long
            Get
                Return m_AC_NO_IN_HOUSEHOLD
            End Get
            Set(value As Long)
                m_AC_NO_IN_HOUSEHOLD = value
            End Set
        End Property
        Public Property NumberOfVehicles() As Long
            Get
                Return m_AC_VEHICLES_IN_HOUSEHOLD
            End Get
            Set(value As Long)
                m_AC_VEHICLES_IN_HOUSEHOLD = value
            End Set
        End Property
    End Class
#End Region

End Class

[kleinma]

You could make the constructor of the nested class Protected Friend. Your IncomeExpenditure can create an instance of it internally because it is "friend", but code that has a reference to your DLL won't be able to create a direct instance of it.

[Evil_Giraffe]

Enforcing this will be complicated, are you sure it's worth it? What is the issue if an application instantiates an instance of the class?

You'd also want the constructor to be just Friend if you went that route, otherwise another assembly could create a class derived from your nested class. Not only would the application then be able to create instances of a type derived from your nested class (which I'm assuming is just as "bad"), but it would also be able to ask that derived class to create instances of the nested class directly (non-derived) as it has full access to the constructor through the Protected modifier.

[Niya]

You could use interfaces:-

Public Interface IEmploymentInfo
    Property Address As String
    Property EmployerName As String
    Property CompanyName As String
End Interface
 
Public Class Person
 
    Private _employment As EmploymentInfo
 
    Public Property Name As String
    Public Property Age As Integer
 
    Public Property Employment As IEmploymentInfo
        Get
            If _employment Is Nothing Then
                _employment = New EmploymentInfo
            End If
            Return _employment
        End Get
        Set(value As IEmploymentInfo)
 
        End Set
    End Property
 
    Private Class EmploymentInfo
        Implements IEmploymentInfo
 
 
        Public Sub New()
 
        End Sub
 
        Public Property Address As String Implements IEmploymentInfo.Address
        Public Property CompanyName As String Implements IEmploymentInfo.CompanyName
        Public Property EmployerName As String Implements IEmploymentInfo.EmployerName
    End Class
 
End Class

The class itself is private inside its parent class but the interface is public so you can access the members outside the class through the interface but without access to the concrete class, one cannot instantiate it outside of its parent.