(커피한잔!) 링크드리스트 베이직 class

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Option Explicit

'
' A simple doublely linked list class
'

Private m_head As clsListItem
Private m_tail As clsListItem
Private m_cur As clsListItem

Private m_count As Long
'
' Adds ItemData to the head of the linked list
'
Public Sub AddFirst(ItemData As Variant)
Dim Item As New clsListItem

If VarType(ItemData) = vbObject Then
Set Item.ItemData = ItemData
Else
Item.ItemData = ItemData
End If

If (m_head Is Nothing) Then
Set m_head = Item
Set m_tail = Item
Set m_cur = Item
Else
Set Item.NextItem = m_head
Set Item.PrevItem = Nothing
Set Item.NextItem.PrevItem = Item
Set m_head = Item
End If

m_count = m_count + 1
End Sub

'
' Adds ItemData to the end of the linked list.
'
Public Sub AddLast(ItemData As Variant)
Dim Item As New clsListItem

If VarType(ItemData) = vbObject Then
Set Item.ItemData = ItemData
Else
Item.ItemData = ItemData
End If

If (m_tail Is Nothing) Then
Set m_head = Item
Set m_tail = Item
Set m_cur = Item
Else
Set Item.PrevItem = m_tail
Set Item.NextItem = Nothing
Set Item.PrevItem.NextItem = Item
Set m_tail = Item
End If

m_count = m_count + 1
End Sub

'
' Returns the number of items in the linked list.
'
Property Get Count() As Long
Count = m_count
End Property

'
' Returns the current item.
'
Property Get CurrentItem() As Variant
If m_cur Is Nothing Then
CurrentItem = Null
Else
If VarType(m_cur.ItemData) = vbObject Then
Set CurrentItem = m_cur.ItemData
Else
CurrentItem = m_cur.ItemData
End If
End If
End Property

'
' Sets the current item.
'
Property Let CurrentItem(ItemData As Variant)
If Not m_cur Is Nothing Then
m_cur.ItemData = ItemData
End If
End Property
Property Set CurrentItem(ItemData As Variant)
If Not m_cur Is Nothing Then
Set m_cur.ItemData = ItemData
End If
End Property
'
' Inserts ItemData after the current item in the list.
'
Public Sub InsertAfter(ItemData As Variant)
Dim Item As New clsListItem

If VarType(ItemData) = vbObject Then
Set Item.ItemData = ItemData
Else
Item.ItemData = ItemData
End If

If (m_cur Is Nothing) Then
Set m_head = Item
Set m_tail = Item
Set m_cur = Item
Else
Set Item.NextItem = m_cur.NextItem
Set Item.PrevItem = m_cur
Set m_cur.NextItem = Item
'Add the following line.
Set m_cur.NextItem.PrevItem = Item

If (m_cur.NextItem Is Nothing) Then
Set m_tail = m_cur
End If
End If

m_count = m_count + 1
End Sub

'
' Delete's the
'
Public Sub DeleteAll()
Dim m As clsListItem
Dim m2 As clsListItem

m = m_head

Do While Not (m Is Nothing)
Set m2 = m.NextItem
Set m.NextItem = Nothing
Set m.PrevItem = Nothing
Set m = m2
Loop

m_head = Nothing
m_tail = Nothing
m_cur = Nothing
m_count = 0
End Sub

Public Sub DeleteCurrent()
Dim tmp As clsListItem

If (m_cur Is Nothing) Then
Exit Sub
End If

If (m_cur.PrevItem Is Nothing) Then
'
' Delete head of list
'
Set m_head = m_cur.NextItem
If (m_head Is Nothing) Then
'
' Also deleting tail, list becomes empty
'
Set m_tail = Nothing
Set m_cur = Nothing
Else
Set m_head.PrevItem = Nothing
Set m_cur = m_head
End If
ElseIf (m_cur.NextItem Is Nothing) Then
'
' Deleting end of list
'
Set m_tail = m_cur.PrevItem
If (m_tail Is Nothing) Then
'
' Also deleting head, list becomes empty
'
Set m_head = Nothing
Set m_cur = Nothing
Else
Set m_cur = m_tail
Set m_cur.NextItem = Nothing
End If
Else
'
' Delete somewhere inside of list
'
Set tmp = m_cur.NextItem
Set m_cur.PrevItem.NextItem = m_cur.NextItem
Set m_cur.NextItem.PrevItem = m_cur.PrevItem
Set m_cur = tmp
End If

m_count = m_count - 1
End Sub
'
' Return's the first item in the list.
'
Public Function FirstItem() As Variant
If (m_head Is Nothing) Then
FirstItem = Null
Else
If (VarType(m_head.ItemData) = vbObject) Then
Set FirstItem = m_head.ItemData
Else
FirstItem = m_head.ItemData
End If
Set m_cur = m_head
End If
End Function

'
' Returns the next item in the list.
'
Public Function NextItem() As Variant
If (m_cur Is Nothing) Then
NextItem = Null
Debug.Print "First Null"
Else
If (m_cur Is Nothing) Then
NextItem = Null
Else
Set m_cur = m_cur.NextItem
If (VarType(m_cur.ItemData) = vbObject) Then
Set NextItem = m_cur.ItemData
Else
NextItem = m_cur.ItemData
End If
End If
End If
End Function

'
' Returns the last item in the list.
'
Public Function LastItem() As Variant
If (m_tail Is Nothing) Then
LastItem = Null
Else
Set m_cur = m_tail
If (VarType(m_cur.ItemData) = vbObject) Then
Set LastItem = m_cur.ItemData
Else
LastItem = m_cur.ItemData
End If
End If
End Function

'
' Returns the previous item in the list.
'
Public Function PrevItem() As Variant
If (m_cur Is Nothing) Then
PrevItem = Null
Else
If (m_cur.PrevItem Is Nothing) Then
PrevItem = Null
Else
Set m_cur = m_cur.PrevItem
If (VarType(m_cur.ItemData) = vbObject) Then
Set PrevItem = m_cur.ItemData
Else
PrevItem = m_cur.ItemData
End If
End If
End If
End Function