Question

I am trying to retrieve the correct value from an ArrayList of objects (.NET 1.1 Framework):

I have the following defined:

Public AlList As New ArrayList

Public Class ItemInfo
    Public ItemNo As Int16
    Public ItemType As String
    Public Reports As Array
    Public PDFs As Array
End Class

The form_load event code contains:

Dim AnItemObj As New ItemInfo

Then a loop that includes:

AnItemObj.ItemNo = AFile.RecordId
AnItemObj.ItemType = temp
AlList.Add(AnItemObj)

So I should now have an ArrayList of these objects, however if I try to retrieve the data:

MsgBox(AlList(5).ItemNo)

I always get the ItemNo of the last value in the list.

What am I missing?

Answer 1

Put the following code:

Dim AnItemObj As New ItemInfo

inside the loop which adds AnItemObj to the list.

When you add a reference type to a list, you are only adding the reference, not the value.

This means that if you add 10 times the same instance to a list, it will add 10 times the same reference to the list. But if afterward you still have a reference to this instance you can modify its properties and as all 10 entries in the list point to the same reference in memory, all 10 entries will be modified.