List inside List. Is that possible?

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I need that one property of a list will be other list, is posible??

I am trying something like:

VB

Public Class List1
        Private _aaaa As String
        Private _bbbb As String
        Private _dddd As List2
        Public Property aaaa() As String
            Get
                Return _aaaa
            End Get
            Set(ByVal value As String)
                _aaaa = value
            End Set
        End Property
        Public Property bbbb() As String
            Get
                Return _bbbb
            End Get
            Set(ByVal value As String)
                _bbbb = value
            End Set
        End Property
        Public Property dddd As List2
            Get
                Return _dddd
            End Get
            Set(ByVal value As List2)
                _dddd = value
            End Set
        End Property
End Class

Public Class List2
        Private _eeee As Integer
        Private _ffff As String
        Public Property _eeee As Integer
            Get
                Return _eeee
            End Get
            Set(ByVal value As Integer)
                _eeee = value
            End Set
        End Property
        Public Property ffff As String
            Get
                Return _ffff
            End Get
            Set(ByVal value As String)
                _ffff = value
            End Set
        End Property
End Class


Public Class List1
        Inherits List(Of List1)
End Class
Public Class List2
        Inherits List(Of List2)
End Class

But when try to charge the List2 i get one exception "null value" because List2 is not initialitated

VB

For I = 0 To 6

     For X = 0 To 5
          Lista1(I).List2(X).eeee = 1
          Lista1(I).List2(X).ffff = 1
     Next

Next

What am i doing wrong?

Posted 12-Oct-13 5:30am

Aitor ares

Updated 12-Oct-13 7:59am

Mike Meinz

v2

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Mike Meinz · Answer 1 · 2013-10-12T07:58:00

You have to instantiate List2. Declaring it does not instantiate it. See Private _dddd As List2 = New List2 in the Public Class List1 below.

Don't forget that you will have to instantiate List1, also.

In your nested For..Next loops, you are treating your classes as though they are arrays that have been declared with a set number of array cells. Nowhere in your classes do you allocate cells to hold the values that you are assigning in your For..Next loop.

See the Microsoft documentation for List <t> Class[^] for ideas on some of the "features" that your List classes must support.

VB.NET

Public Class List1
        Private _aaaa As String
        Private _bbbb As String
        Private _dddd As List2 = New List2
        Public Property aaaa() As String
            Get
                Return _aaaa
            End Get
            Set(ByVal value As String)
                _aaaa = value
            End Set
        End Property
        Public Property bbbb() As String
            Get
                Return _bbbb
            End Get
            Set(ByVal value As String)
                _bbbb = value
            End Set
        End Property
        Public Property dddd As List2
            Get
                Return _dddd
            End Get
            Set(ByVal value As List2)
                _dddd = value
            End Set
        End Property
End Class

Aitor ares · Answer 2 · 2013-10-12T10:00:00

Solution 2

Thank you very much for your answer Mike Meinz. In the main program I instantiate the list1

VB

Dim Lst As Lista1
For I = 0 To 6
     For X = 0 To 5
          Lista1(I).List2(X).eeee = 1
          Lista1(I).List2(X).ffff = "pP"
     Next
Next

but now the error is ArgumentoutofrangeException. The error is in Lista1(I).List2(X).eeee =1

Do you know why? Thx again!!

Posted 12-Oct-13 10:00am

Aitor ares

Comments

Mike Meinz 12-Oct-13 16:08pm

Please do not post followups as a separate Solution. Use "Have a Question or Comment" link.

Mike Meinz 12-Oct-13 16:15pm

See revised Solution 1.