VB adding to a list when initializing a constructor

Question

I have been stuck for the past hour trying to initialize "one" card in my deck of cards. Everything works create but as soon as I try to add a Card to my deck I get a "null reference exception" error. I created a card with a value of 1 and 12 (suit, value) and try to add "the card object" to my list of cards. The values show up when I message box the information but my list will not take the card.

      Public Class deck
          'create the fields
          Private newDeck As List(Of Card)

          'create properties
          Property newDeck_Property As List(Of Card)
            Get
                Return newDeck
            End Get
            Set(value As List(Of Card))
                newDeck = value
            End Set
         End Property


      Sub New()
            Dim cardvalueinfo As CardValue
            cardvalueinfo.cSuite = 1
            cardvalueinfo.cValue = 12
            Dim newCardinsert As New Card(cardvalueinfo)
            MessageBox.Show(newCardinsert.oneCard_Prop.cSuite)
            MessageBox.Show(newCardinsert.oneCard_Prop.cValue)
            newDeck_Property.Add(newCardinsert) <--------------- null error here
      End Sub

  End Class

I would really appreciate anyone pointing me in the right direction. I am a noob

Thanks

before you go much further consider initializing the deck List with all the cards and then shuffling them. see this answer and this sample). You'll almost certainly be unhappy with the results of picking a random card from the deck list. — Ňɏssa Pøngjǣrdenlarp
– Ňɏssa Pøngjǣrdenlarp, Commented Mar 3, 2014 at 2:25

har07 · Accepted Answer · 2014-03-03 02:13:35Z

2

You need to initialize newDeck_Property before adding item to it :

newDeck_Property = New List(Of Card)

or put initialization along with declaration of the backing field :

Private newDeck As New List(Of Card)

answered Mar 3, 2014 at 2:13

har07

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2 Comments

user3363744 Over a year ago

Thank you! They both worked. Why wouldnt i need to initialize both of them as new? Why do I only need to do one of them. It seems like to me when you put New you are create a new list, so why would I need to initialize both lists (if that makes sense)

har07 Over a year ago

the 1st snippet above, implicitly assign newly created List(Of Card) to the backing field (newDeck). The 2nd snippet, implicitly pass newly created List(Of Card) to getter of newDeck_Property whenever the property being accessed. Doing both at the same time will also work, but useless. Can't explain better, hope you get the idea :)

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