vb.net 2003 Arraylist of structure which have an arraylist - vb.net

Question

I have two structures
Public Structure myResearchData
Public batchName As String
Public arraylistRData As ArrayList
End Structure
Public Structure myResearchSubData
Public researchDescription As String
Public recordingDate As Date
Public book As String
Public page As String
Public year As String
Public fee As String
End Structure
I initialize them in a sub
Dim MyResearchDataAList As New ArrayList
Dim MyResearchData As myResearchData
MyResearchData.arraylistRData = New ArrayList
Dim MyResearchSubData As myResearchSubData
I have an arraylist of myResearchSubData which is MyResearchData.arraylistRData and added it inside MyResearchDataAList. But when I cleared MyResearchData.arraylistRData the arraylist inside MyResearchDataAList is also cleared. I thought that once it is added to MyResearchDataAList it will hold the arraylist but it is also clered. Below is the process that I have done.
MyResearchSubData.recordingDate = Date.Parse(Date)
MyResearchSubData.book = Book
MyResearchSubData.page = Page
MyResearchSubData.year = Year
MyResearchSubData.fee = Fee
Put data in the structure of MyResearchSubData
MyResearchData.arraylistRData.Add(MyResearchSubData)
Added it in MyResearchData.arraylistRData
MyResearchDataAList.Add(MyResearchData)
Added it in MyResearchDataAList
MyResearchData.arraylistRData.Clear()
Cleared MyResearchData.arraylistRData for new data to be put in but it also clears the arraylist inside MyResearchDataAList and didn't old the contents of the arraylist
Thanks in advance for those who can help me with this problem

Answer 1

That is happening because it is actually the same items being added to the array list, as they are added by reference. You want to actually add a COPY of each item to your arrayList.
I generally find the easiest way to do something like that is to add a clone of the object during a loop.
To do that you may need to implement ICloneable to get the proper copy. At the level of the myResearchSubData however, it appears that you can just use the memberwiseClone Method.
If you change the to a class instead of a structure you can use the clone like this:
Public Class myResearchSubData
Implements ICloneable
Public researchDescription As String
Public recordingDate As Date
Public book As String
Public page As String
Public year As String
Public fee As String
Public Function Clone() As Object Implements System.ICloneable.Clone
Return Me.MemberwiseClone
End Function
End Class
Then you would want to loop through your original list of myResearchSubData and add its clone to the second list. Something like:
For Each item as myResearchSubData in MyResearchData.arraylistRData
MyResearchDataAList.Add(CType(item.Clone, myResearchSubData))
Next
If you want to continue to use the structures then I would use the same loop type and make a function that creates a new myResearchSubData and copies the data from the original over to the new one.
For Each item as myResearchSubData in MyResearchData.arraylistRData
MyResearchDataAList.Add(CloneStructure(item))
Next