inheritance in VB.net - vb.net

Question

Not real sure how to ask this question... Some of my terms may be incorrect but hopefully I'll be able to get the question across. If I have a class something like this
Public Class Agency
public property ID as integer=0
public property Name as string=string.empty
Public sub new()
end sub
end class
and then a factory class that returns a list
Public Class Agency_Controller
Public Sub New()
end sub
Public function Fetch() as list(of Agency)
pop the list and return it
end function
end class
If I create another class say Agency_Misc and want to inherit the Agency Class I get, how to do that?
Public Class Agency_Misc
inherits Agency
public property Address as string=string.empty
end class
Now if I want to use the Agency_Misc, how do I get the Agency_Controller Fetch function? In the code if I were going after the agency... I do something like
Dim oS as list(of Agency)=nothing
dim oC as new Agency_Controller
os=oc.Fetch()
but if I want my list to have the list(of Agency_Misc) (because I was doing some more stuff)
how do I do that. I can't change list(of Agency) to list(of Agency_Misc) because it will tell me it can't convert it I think it was.
Anyway... I'd like to learn what it is I'm missing or what other approach I need to look into.

Answer 1

If you have defined your classes properly, you can do the following:
Define a BaseClass.
Define a DerivedClass which inherits from BaseClass
Define a List(Of BaseClass) and populate it with objects of DerivedClass (the List will accept objects of Dervived class, because these are, through inheritance, also objects of BaseClass.
Access the items in the list with a variable of Type DerivedClass.
What you CAN'T do is populate the list with objects of type BaseClass, and then attempt to access them using a variable of Type DerivedClass.
Ex. #1 THIS will work:
Public Class Form1
Private MyListOfBaseCLass As List(Of MyBaseClass)
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
MyListOfBaseCLass = New List(Of MyBaseClass)
Dim dc As New MyDerivedCLass("City of Portland", "555 SW 5th Avenue")
MyListOfBaseCLass.Add(dc)
dc = New MyDerivedCLass("City of Salem", "222 E River Road")
MyListOfBaseCLass.Add(dc)
dc = New MyDerivedCLass("City of Denver", "333 SomeStreet")
MyListOfBaseCLass.Add(dc)
End Sub
Private Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
For Each dc As MyDerivedCLass In MyListOfBaseCLass
MsgBox(dc.MyName & ", " & dc.MyAddress)
Next
End Sub
End Class
THIS will FAIL:
Public Class Form1
Private MyListOfBaseCLass As List(Of MyBaseClass)
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
MyListOfBaseCLass = New List(Of MyBaseClass)
Dim dc As New MyBaseClass("City of Portland")
MyListOfBaseCLass.Add(dc)
dc = New MyBaseClass("City of Salem")
MyListOfBaseCLass.Add(dc)
dc = New MyBaseClass("City of Denver")
MyListOfBaseCLass.Add(dc)
End Sub
Private Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
For Each dc As MyDerivedCLass In MyListOfBaseCLass
MsgBox(dc.MyName & ", " & dc.MyAddress)
Next
End Sub
End Class

Answer 2

You best set the properties in the constructor
Public Class Agency
Private m_ID As Integer
Public Property ID() As Integer
Get
Return m_ID
End Get
Set(ByVal value As Integer)
m_ID = value
End Set
End Property
Private m_name As String
Public Property Name() As String
Get
Return m_name
End Get
Set(ByVal value As String)
m_name = value
End Set
End Property
Sub New(ByVal id As Integer, ByVal name As String)
Me.m_ID = id
Me.m_name = name
End Sub
End Class
...
Dim HiDollar as New Agency(100, "High Dollar")