ArrayList.Sort in Inherited Classes

[samsmithnz]

I have a class (clsItem), that I use to inherit in all my other classes. It looks like this (very straight forward):

Public Class clsItem

   Implements IComparer

   Private intItemKey As Integer
   Private strName As String
   Private lngBuyPrice As Long

   Overridable Function Compare(ByVal x As Object, ByVal y As Object) As Integer Implements IComparer.Compare
       Compare = x.ItemKey < y.ItemKey
   End Function

   Public Property ItemKey() As Integer
       Get
           ItemKey = intItemKey
       End Get
       Set(ByVal Value As Integer)
           intItemKey = Value
       End Set
   End Property

   Public Property Name() As String
       Get
           Name = strName
       End Get
       Set(ByVal Value As String)
           strName = Value
       End Set
   End Property

   Public Property BuyPrice() As Long
       Get
           BuyPrice = lngBuyPrice
       End Get
       Set(ByVal Value As Long)
           lngBuyPrice = Value
       End Set
   End Property

End Class

 

I have about 10 other classes that inherit this clsItem. I then read from a database and load each type of item into the right class, then each object is loaded into an arraylist. I'm now trying to sort the collection on the ItemKey field (inherited from clsItem).

 

Unfortunetly this isn't working out. I get this error:

System.InvalidOperationException: Specified IComparer threw an exception. ---> System.ArgumentException: At least one object must implement IComparable.
  at System.Collections.Comparer.Compare(Object a, Object b)
  at System.SorterObjectArray.QuickSort(Int32 left, Int32 right)
  --- End of inner exception stack trace ---
  at System.SorterObjectArray.QuickSort(Int32 left, Int32 right)
  at System.Array.Sort(Array keys, Array items, Int32 index, Int32 length, IComparer comparer)
  at System.Array.Sort(Array array, Int32 index, Int32 length, IComparer comparer)
  at System.Collections.ArrayList.Sort(Int32 index, Int32 count, IComparer comparer)
  at System.Collections.ArrayList.Sort()
  at XClone.modDataAccess.LoadUFOPedia(XmlDocument objXMLDoc) in C:\Projects\Xclone\modDataAccess.vb:line 121

 

What do I have to do to get this to work? I thought that implementing my overidden compare function in the clsItem would be enough, but this error message seems to be saying otherwise?

 

any ideas brainy-acs???

[samsmithnz]

If this isn't possible, maybe I should write my own sorting algorithm???

[PlausiblyDamp]

insteam of implementing IComparer try using IComparable, delete the implements statement and your Compare function and paste this in it's place and see if it works.

 

Implements IComparable

Public Function CompareTo1(ByVal obj As Object) As Integer Implements System.IComparable.CompareTo
	Dim x As clsItem = DirectCast(obj, clsItem)

	If ItemKey > x.ItemKey Then Return 1
	If ItemKey < x.ItemKey Then Return -1
	Return 0
End Function

[samsmithnz]

Thanks PlausiblyDamp, you're amazing, that works perfectly!