Debugging Help Please

I've created a doubley linked list via classes. That whole list works fine. I can traverse it no problem. However, values I store in each node aren't saved/carried over. The following lines are where the problem is noticed:

1) list.lastNode = New clsNode(x, y)
2) list.firstNode = list.lastNode

and

1) currentNode = New clsNode(x, y, , list.firstNode)
2) list.firstNode.prevNode = currentNode

lets say y = 100 in line (1), when I execute the line (2), Y is still set to the default 0 for node. Why aren't the values kept? I've verified that the x and y values carry over to the clsNode::New sub. I know its probably something small i'm overlooking. I've tried using structures instead, but same problem occurs. Following is my stripped down code. Thanx.

Code:

---

Public Class clsNode
        Public point As PointF
        Public prevNode As clsNode
        Public nextNode As clsNode

        Public Sub New(ByVal x As Single, ByVal y As Single, Optional ByVal prev As clsNode = Nothing, Optional ByVal nxt As clsNode = Nothing)     
            Dim point As New PointF(x, y)

            Me.prevNode = prev
            Me.nextNode = nxt
        End Sub
End Class

Public Class clsList
        Public firstNode As clsNode = Nothing  '//First node in entire list
        Public lastNode As clsNode = Nothing    '//Last node in entire list
End Class

Public Class frmCG
    Public currentNode As clsNode  '//Used to iterate through the list
    Private testList As New clsList

    Private Sub addValue(ByRef list As clsList, ByVal value As Single)
        Dim x As Single = 0
        Dim y As Single = 150 - value

        If (list.firstNode Is Nothing) Then    '//If list hasn't been started yet
            list.lastNode = New clsNode(x, y)
            list.firstNode = list.lastNode
        Else    '//Else push_front
            currentNode = New clsNode(x, y, , list.firstNode)
            list.firstNode.prevNode = currentNode
            list.firstNode = currentNode
            Do
                currentNode = currentNode.nextNode
                currentNode.point.X += 2
            Loop Until (currentNode.nextNode Is Nothing)
        End If
    End Sub
End Class

---

Note testList is passed to sub AddValue from some other arbitruary sub.

Well I've worked around the problem by assigning the values outside of the new sub. However I'm still curious why those values didn't "Save". Does anyone have any idea why? Thanx.

Quote:

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Originally Posted by SourSW

I've created a doubley linked list via classes. That whole list works fine. I can traverse it no problem. However, values I store in each node aren't saved/carried over. The following lines are where the problem is noticed:

1) list.lastNode = New clsNode(x, y)
2) list.firstNode = list.lastNode

and

1) currentNode = New clsNode(x, y, , list.firstNode)
2) list.firstNode.prevNode = currentNode

lets say y = 100 in line (1), when I execute the line (2), Y is still set to the default 0 for node. Why aren't the values kept? I've verified that the x and y values carry over to the clsNode::New sub. I know its probably something small i'm overlooking. I've tried using structures instead, but same problem occurs. Following is my stripped down code. Thanx.

Code:

---

Public Class clsNode
        Public point As PointF
        Public prevNode As clsNode
        Public nextNode As clsNode

        Public Sub New(ByVal x As Single, ByVal y As Single, Optional ByVal prev As clsNode = Nothing, Optional ByVal nxt As clsNode = Nothing)     
            Dim point As New PointF(x, y)

            Me.prevNode = prev
            Me.nextNode = nxt
        End Sub
End Class

Public Class clsList
        Public firstNode As clsNode = Nothing  '//First node in entire list
        Public lastNode As clsNode = Nothing    '//Last node in entire list
End Class

Public Class frmCG
    Public currentNode As clsNode  '//Used to iterate through the list
    Private testList As New clsList

    Private Sub addValue(ByRef list As clsList, ByVal value As Single)
        Dim x As Single = 0
        Dim y As Single = 150 - value

        If (list.firstNode Is Nothing) Then    '//If list hasn't been started yet
            list.lastNode = New clsNode(x, y)
            list.firstNode = list.lastNode
        Else    '//Else push_front
            currentNode = New clsNode(x, y, , list.firstNode)
            list.firstNode.prevNode = currentNode
            list.firstNode = currentNode
            Do
                currentNode = currentNode.nextNode
                currentNode.point.X += 2
            Loop Until (currentNode.nextNode Is Nothing)
        End If
    End Sub
End Class

---

Note testList is passed to sub AddValue from some other arbitruary sub.

---

if you observe closely, u passing the value of y = 100, in the contructor, but u are not assigning it to any attribute of the class, that's where the problem is.

I'm not sure what you mean. I use it when creating a new point. Shouldn't that be assigning it to the pointF variable?

Your problem is in the constructor

Code:

---

Public Class clsNode
        Public point As PointF
        Public prevNode As clsNode
        Public nextNode As clsNode

        Public Sub New(ByVal x As Single, ByVal y As Single, Optional ByVal prev As clsNode = Nothing, Optional ByVal nxt As clsNode = Nothing)     

----> this is the problem            Dim point As New PointF(x, y)
----> you're instancing a new point and declaring a new POINT variable and
you never assign it to me.point.

----> you can either do this
      me.point = New pointF(x,y)
---->
or
      dim point as new pointF(x,y)
      me.point = point


            Me.prevNode = prev
            Me.nextNode = nxt
        End Sub
End Class

---

Just like Ambreesh pointed out.

Oh. I had always assumed that it automatically assigned it with the new keyword. Thanx.