[VB6] Implementing LinkedList structure

[DOOM]

Hi.  I started work on implementing a LinkedList structure in VB6, but it's giving me crap...  I'm more used to doing this sort of thing in Java, so I'm hoping maybe some of you know more about dealing with this sort of thing in Visual Basic.

This is from the LinkedList.cls

Code Select Expand


Option Explicit

Private varHead As New LinkedListElement
Private lngSize As Long
Private bIsEmpty As Boolean

Public Sub Init()
   Set varHead = Nothing
   lngSize = 0
   bIsEmpty = True
End Sub

Public Sub add(ByVal value As Variant)
   If (varHead Is Nothing) Then
       If IsObject(value) Then
           Set varHead.setValue = value
       Else
           varHead.setValue = value
       End If
       Set varHead.setNextElement = Nothing
   Else
       Dim insert As LinkedListElement
       Set insert = New LinkedListElement
       If IsObject(value) Then
           Set insert.setValue = value
       Else
           insert.setValue = value
       End If
       Set insert.setNextElement = Nothing
       Dim temp As New LinkedListElement
       Dim bFound As Boolean
       bFound = False
       Set temp = varHead
       Dim newElement As LinkedListElement
       Do While (bFound <> True)
           Set newElement = temp.getNextElement
           If (newElement Is Nothing) Then
               Set temp.setNextElement = insert
               bFound = True
           Else
               Set temp = newElement
           End If
       Loop
   End If
   lngSize = lngSize + 1
   bIsEmpty = False
End Sub

Public Sub remove(ByVal value As Variant)
   If (varHead <> Nothing) Then
       Dim tempElement As LinkedListElement
       Dim tempVal As Variant
       Set tempElement = varHead
       If (IsObject(tempElement.getValue)) Then
           Set tempVal = tempElement.getValue
       Else
           tempVal = tempElement.getValue
       End If
       If (value = tempVal) Then
           Set tempElement = tempElement.getNextElement
           If (tempElement <> Nothing) Then
               Set varHead = tempElement
           Else
               Set varHead = Nothing
               bIsEmpty = True
           End If
           lngSize = lngSize - 1
       Else
           Dim previous As New LinkedListElement
           Set previous = tempElement
           Set tempElement = tempElement.getNextElement
           While (tempElement <> Nothing)
               If (IsObject(tempElement.getValue)) Then
                   Set tempVal = tempElement.getValue
               Else
                   tempVal = tempElement.getValue
               End If
               If (value = tempvalue) Then
                   Dim tempNext As New LinkedListElement
                   Set tempNext = tempElement.getNextElement
                   previous.setNextElement = tempNext
                   lngSize = lngSize - 1
               Else
                   Set previous = tempElement
                   Set tempElement = tempElement.getNextElement
               End If
           Loop
       End If
   End If
End Sub

Public Function isEmpty() As Boolean
   isEmpty = bIsEmpty
End Function

Public Function getSize() As Long
   getSize = lngSize
End Function

Public Property Get getHead() As LinkedListElement
   Set getHead = varHead
End Property


And this is from the LinkedListElement.cls:

Code Select Expand


Option Explicit

Private value As Variant 'value to be stored in this element
Private varNextElement As LinkedListElement 'next element in the list

'change the next element in the list to a new element
Public Property Set setNextElement(ByVal newNext As LinkedListElement)
   Set varNextElement = newNext
End Property

'return the next element in the list
Public Property Get getNextElement() As LinkedListElement
   Set getNextElement = varNextElement
End Property

'change the value stored in this element (if it is a primitive type)
Public Property Let setValue(ByVal newValue As Variant)
   value = newValue
End Property

'change the value stored in this element (if it is an object type)
Public Property Set setValue(ByVal newValue As Variant)
   Set value = newValue
End Property

'return the value stored in this element
Public Property Get getValue()
   If (IsObject(value)) Then
       Set getValue = value
   Else
       getValue = value
   End If
End Property


I was testing it like this:

Code Select Expand


   Dim ll As New LinkedList
   ll.Init
   
   Dim l1 As New LinkedListElement
   l1.setValue = "test1"
   
   ll.add l1

   Dim l2 As New LinkedListElement
   l2.setValue = "test2"
   
   ll.add l2
   
   Dim iterate As LinkedListElement
   Set iterate = ll.getHead
   
   lbl.Caption = iterate.getValue


No matter what I've done, iterate.getValue doesn't seem to return anything.  The isEmpty and getSize functions both return results correctly (ie: telling me that I have added two items to the LinkedList).

Sorry about the long post, but I thought I'd try and give you as much information to work with as I could as opposed to giving too little.  I'd really appreciate any help any of you could give.  Thanks.

[Grok]

Public Property Get getValue()

Try returning a Variant type?  "As Variant"
Did you step through Property Get getValue?  While in that property, is the value of Value correct?

[DOOM]

Hey I think I found the problem.  VB wants you to do stuff like this:

dim var as linkedlistelement
set var = new linkedlistelement

It hates me if I try to combine those.
Ie: dim var as new linkedlistelement

So I went through and changed my code in the declarations and add methods and so far it seems to be working.  I still need to go through and test the remove method.  But so far, so good.

Thanks for the help Grok, it really helped just having someone else looking at it too.  I really appeciate the assist.