VB.NET problem has me baffled

sunama

sunama

sunama

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Right gents I've been feverishly developing my natural language processing program and today, for the first time I encountered something that completely baffled me. I solved, but I had to use a very dirty solution, which is not ideal.

Perhaps some VB.NET expert can tell me what the hell is going on.

Below is my main subroutine, which calls the function (IsSimilarUserRecord) below it.

I haven't pasted all the code for IsSimilarUserRecord, as it is not important.


The parts I want you to take a look at are in bold (purple and pink)

main sub:

Public Sub CompileShortListOfSimilarUserRecordsMain(ByVal mainUserRecordID As String, ByVal clientID As Integer, ByRef shortListOfSimilarUserRecordIDs As ArrayList) 'Optional ByVal userRecordLineContents As String = "")
If String.IsNullOrEmpty(mainUserRecordID) Then
errorLog.Add("ERROR179: record id input is empty (" & mainUserRecordID & "). Unable to compile short lilst of similar user records.")
Exit Sub
End If


'we can't start a new short list until the previous short list has been completely emptied of user records
shortListOfSimilarUserRecordIDs.Clear()
shortListOfSimilarUserRecordIDs.Add("")

'now load up the fields of the main user record into an array list
Dim mainUserRecordFieldsArrayList As New ArrayList
mainUserRecordFieldsArrayList = userRecordArrayHandler.ReturnGenericFieldsInArrayList(mainUserRecordID)
mainUserRecordFieldsArrayList.Sort()

'now go through all the user records which apply to the current user
'load all the user record fields into arraylists, one by one.

Dim arrayProcessor As New ArrayProcessingClass
Dim localUserRecordIDAL As New ArrayList
localUserRecordIDAL = clientInfoHolder(clientID).GetUserRecordIDArrayList

Dim URIDIndexMax As Integer = localUserRecordIDAL.Count - 1
For URIDIndex = 1 To URIDIndexMax 'do for each user record loaded in memory
Dim tempURID As String = localUserRecordIDAL(URIDIndex).ToString
Dim tempURGenericFieldArrayList As New ArrayList
tempURGenericFieldArrayList = userRecordArrayHandler.ReturnGenericFieldsInArrayList(tempURID)
tempURGenericFieldArrayList.Sort()

Dim textProcessing As New TextProcessingClass
If arrayProcessor.ArrayListStringEquals(mainUserRecordFieldsArrayList, tempURGenericFieldArrayList) Then
'do nothing 'ignore the identical user record
ElseIf (IsSimilarUserRecord(mainUserRecordFieldsArrayList, tempURGenericFieldArrayList)) Then 'check if user record array is similar to new user record
'if it is we add the user record id to the short list
shortListOfSimilarUserRecordIDs.Add(tempURID)
End If
Next URIDIndex

'if none found
If shortListOfSimilarUserRecordIDs.Count < 2 Then 'count = 0 or 1
shortListOfSimilarUserRecordIDs.Clear()
End If
End Sub



Public Function IsSimilarUserRecord(ByVal arraylist1 As ArrayList, ByVal arraylist2 As ArrayList, Optional ByVal allowableNumberOfElementsToBeNonIdentical As Integer = 1) As Boolean
'stuff
End Function





Now what is happening is that in the purple line I am calling IsSimilarUserRecord. All arguments are passed, Byval (not Byref). When I call IsSimilarUserRecord for the first time, mainUserRecordFieldsArrayList and tempURGenericFieldArrayList are passed into IsSimilarUserRecord without a problem. However, when IsSimilarUserRecord returns its boolean value, the 2 array lists: mainUserRecordFieldsArrayList and tempURGenericFieldArrayList are both emptied of their contents. This should not be happening, as their contents were passed ByVal, so should be unaltered after the boolean value is returned.

In itself this wouldn't be a problem but because the contents of mainUserRecordFieldsArrayList have to be repeatedly used (as it is contained in a For loop), after the 1st loop, that array list is useless.

Can somebody explain to me why the array lists are getting emptied, whenever I call IsSimilarUserRecord and pass the 2 array to it?

Thanks
 
Thanks for your reply.

Haircut said:
If you really want a copy of the object you'll need to clone the contents.
Click to expand...

This is what I was forced to do in the main sub. It is a dirty solution and not as elegant as the previous (simple) if statement I previously had in place. I then send this copied version into IsSimilarUserRecord, where the array lists are being cleared (for some reason).

Haircut said:
I should ask why you're clearing the contents of the ArrayLists in the subroutine though?
Click to expand...

Are you referring to: shortListOfSimilarUserRecordIDs array list?

Haircut said:
I would expect that a method named IsSimilarUserRecord does not make any modifications to its inputs.
Click to expand...

There are some modifications made by IsSimilarUserRecord, however, this is just to ensure the format of the array lists is correct. In general, after the "modifications", the contents and order of the array list, remains the same. With the input which I am seeing this "error" occur, IsSimilarUserRecord makes no changes to the contents/order of the array lists

Now, I still do not understand why the array lists (in IsSimilarUserRecord), are being emptied?

I can understand that if I clear the 2 array lists (in IsSimilarUserRecord), the array lists in the main sub, will also be cleared (due to the reference type, as you corrected me on, earlier). However, at no stage am I clearing the array lists, with code.

When we reach the end of IsSimilarUserRecord, both array lists are in tact. Yet, the moment we get back to the main sub, those 2 same array lists are empty. Is this due to garbage collection, perhaps?

I'm still baffled.
 
I'm having a play around with this code right now.

I've just passed the arraylists byref and all works as it should I'm suspecting that when I pass the arraylists byval, at the end of IsSimilarUserRecord, garbage collection is involved.

In the final line of IsSimilarUserRecord, BOTH arraylists are fully in tact. Something is happening between the point that IsSimilarUserRecord returns the boolean value and the point that the main sub receives this boolean value. During this time, those 2 arraylists are getting wiped out. This is not happening when the arraylists are passed ByRef.
 
Code: 
    'true if 1 word away. False otherwise
    Private Function IsSimilarUserRecord(ByVal arraylist1 As ArrayList, ByVal arraylist2 As ArrayList, Optional ByVal allowableNumberOfElementsToBeNonIdentical As Integer = 1) As Boolean
        'make sure that the only emptry string in both arrays is in element 0
        Try 'prepare array1
            While arraylist1.Contains("")
                arraylist1.Remove("")
            End While

            While IsNothing(arraylist1(0))
                arraylist1.RemoveAt(0)
            End While

            arraylist1.Insert(0, "")  'now insert a space in position 0
        Catch ex As Exception

        End Try


        Try 'prepare array2
            While arraylist2.Contains("")
                arraylist2.Remove("")
            End While

            While IsNothing(arraylist2(0))
                arraylist2.RemoveAt(0)
            End While

            arraylist2.Insert(0, "")  'now insert a space in position 0
        Catch ex As Exception

        End Try
        ' ------------------------------------------------------------------

        Dim arraylist1Count As Integer = arraylist1.Count
        Dim arraylist2Count As Integer = arraylist2.Count

        If arraylist1Count <> arraylist2Count Then Return False 'if the 2 arrays are of different size, then return false
        If arraylist1Count < 2 Then Return False 'if array list has no elements or only 1 element in it, then return false

        Dim ap As New ArrayProcessingClass
        ap.RemoveDuplicateEntriesInArrayList(arraylist1)
        ap.RemoveDuplicateEntriesInArrayList(arraylist2)

        arraylist1.Sort()
        arraylist2.Sort()

        Dim identicalElementCount As Integer = 0
        Dim maxIndex As Integer = arraylist1Count - 1
        Dim minimumIdenticalElementRequired As Integer = arraylist2Count - allowableNumberOfElementsToBeNonIdentical - 1
        For index = 1 To maxIndex
            Dim tempStringFromArrayList1 As String = arraylist1(index).ToString
            If arraylist2.Contains(tempStringFromArrayList1) Then
                identicalElementCount += 1
            End If
        Next

        Dim isSimilar As Boolean = False
        If identicalElementCount >= minimumIdenticalElementRequired Then
            isSimilar = True
        End If
        Return isSimilar[COLOR="Magenta"] 'at this point, both array lists are fully in tact[/COLOR]
    End Function
 
MrRoper said:
...have you tried commenting the code out of this method and just returning true to see if the same behaviour exists?
Click to expand...

I've just done this.
I set the IsSimilarUserRecord, to accept the arraylists ByVal.

I commented everything out, except for the return value.

It behaves as it should, ie. the array lists are not emptied.

So, for some reason, when I leave the other code in place (inside IsSimilarUserRecord), the array lists are being emptied at the point when the boolean value is returned. However, when that code is commented out, even when the boolean value is returned, the array lists are not being cleared.
 
Haircut said:
Incidentally, which version of .NET are you using?
Click to expand...

3.5.

Haircut said:
you should be using a generic List.
Click to expand...

Thanks for the suggestion...much appreciated.

I was previously used to using (normal) arrays and arraylists, which is why I've kept on using them. I've just checked out Lists and there are definitely some advantages to be had. If we use 'List', I can't see there being any reason to use ArrayList or arrays.

If I were using an earlier version of .NET though, is List, recognised? I don't wish to have issues with earlier versions of .NET, as that would involve a MAJOR code re-write (to accommodate earlier .NET versions).
 
Hi Haircut,

Thats a very nice function you've written then. Makes everything nice and concise.

I may use this, though would this work with older version of .NET?

I've nailed the problem down to the 2 lines of code.
When these are commented out, the function performs as normal. When these 2 lines are left in, the arraylists are cleared after the boolean value is returned back to the calling Sub.

I have posted the code of IsSimilarUserRecord, again, but this time, with the 2 lines of code causing the problem.

Note, that RemoveDuplicateEntriesInArrayList is a sub which removes any duplicate elements from the arraylist. The arrayList is passed ByRef.


Code: 
 'true if 1 word away. False otherwise
    Private Function IsSimilarUserRecord(ByVal arraylist1 As ArrayList, ByVal arraylist2 As ArrayList, Optional ByVal allowableNumberOfElementsToBeNonIdentical As Integer = 1) As Boolean
        'make sure that the only emptry string in both arrays is in element 0
        Try 'prepare array1
            While arraylist1.Contains("")
                arraylist1.Remove("")
            End While

            While IsNothing(arraylist1(0))
                arraylist1.RemoveAt(0)
            End While

            arraylist1.Insert(0, "")  'now insert a space in position 0
        Catch ex As Exception

        End Try


        Try 'prepare array2
            While arraylist2.Contains("")
                arraylist2.Remove("")
            End While

            While IsNothing(arraylist2(0))
                arraylist2.RemoveAt(0)
            End While

            arraylist2.Insert(0, "")  'now insert a space in position 0
        Catch ex As Exception

        End Try
        ' ------------------------------------------------------------------

        Dim arraylist1Count As Integer = arraylist1.Count
        Dim arraylist2Count As Integer = arraylist2.Count

        If arraylist1Count <> arraylist2Count Then Return False 'if the 2 arrays are of different size, then return false
        If arraylist1Count < 2 Then Return False 'if array list has no elements or only 1 element in it, then return false

        Dim ap As New ArrayProcessingClass
[COLOR="Magenta"]        ap.RemoveDuplicateEntriesInArrayList(arraylist1)
        ap.RemoveDuplicateEntriesInArrayList(arraylist2)[/COLOR]

        arraylist1.Sort()
        arraylist2.Sort()

        Dim identicalElementCount As Integer = 0
        Dim maxIndex As Integer = arraylist1Count - 1
        Dim minimumIdenticalElementRequired As Integer = arraylist2Count - allowableNumberOfElementsToBeNonIdentical - 1
        For index = 1 To maxIndex
            Dim tempStringFromArrayList1 As String = arraylist1(index).ToString
            If arraylist2.Contains(tempStringFromArrayList1) Then
                identicalElementCount += 1
            End If
        Next

        Dim isSimilar As Boolean = False
        If identicalElementCount >= minimumIdenticalElementRequired Then
            isSimilar = True
        End If
        Return isSimilar 'at this point, both array lists are fully in tact
    End Function


I'm still baffled as to why the array lists are in tact at the end of IsSimilarUserRecord, but when the boolean value is returned, those same arrayLists, are getting cleared. When those same array lists are passed ByRef, this does not happen. This only happens when using ByVal.

It could simply be that I shall just have to put this down as a mystery.

My current version of code (which does a shallow copy of the array lists, before sending them to IsSimilarUserRecord), works fine, but it is nice to know exactly why the arrayLists are being cleared.
 
Hi.

Backwards compatibility may be important here, with regards to the LINQ function you posted earlier. In which case, I will not include it in my code. However, I do appreciate your help.

I won't post the entire array processing class, as it is too long, but here is the RemoveDuplicateEntriesInArrayList sub:



Code: 
    'input: an arraylist made up strings
    'action: removes all dupicate entries
    Public Sub RemoveDuplicateEntriesInArrayList(ByRef stringArrayList As ArrayList)
        Dim newArrayList As New ArrayList
        newArrayList.Add("")

        While stringArrayList.Contains("")
            stringArrayList.Remove("")
        End While

        Dim indexMax As Integer = stringArrayList.Count - 1
        For index = 0 To indexMax
            Dim tempString As String = stringArrayList(index).ToString

            If Not newArrayList.Contains(tempString) Then
                newArrayList.Add(tempString)
            End If


        Next index

        stringArrayList.Clear()
        [COLOR="Magenta"]stringArrayList = CType(newArrayList.Clone, ArrayList)[/COLOR]

    End Sub


I've also highlighted the line which could be causing the problem here.

Thanks.
 
I spotted this.

After I posted my last post, I was looking closely at the line I've highlighted in pink (above). That's when it clicked that that was the root of all the problems.

I've just made the corrections to that line and have changed it, so that a shallow copy is now what is done (and not a clone). Its now tested and working nicely.

Thank you for your help on this one Haircut...much appreciated.

The key post was Mr Ropers, when he said to comment out the lines in IsSimilarUserRecord. This narrowed down the problem to the line highlighted in pink.

Thank you all for your help.

Haircut, you suggested to perhaps switch to List (and move away from ArrayList). What is the earliest version of .NET that 'List' is recognised? I want to avoid backwards compatibility problems.
 
As I am using so many arraylists (and soon List), I just want to know what I am getting myself into, should I start to use List.

Originally, I was working off of .NET 2.0. Only recently did I make the switch to 3.5, so I'm pretty sure that most of my code is compatible with 2.0.

With regards to the Function not changing the original arraylist. I understand where you are coming from. I "sort of" agree with what you are saying, but for totally unrelated reasons, I have actually made it so that at the start of the Function, the arrayLists are first duplicated and then all the remaining operations are performed on the duplicates. This complies with your way of thinking.

The only reason why the function I pasted had operations on the original inputs was because that particular function is used only by CompileShortListOfSimilarUserRecordsMain. No other sub/function uses it.

The only reason I placed the code into a function was to remove it from the Sub, to improve readability and clutter. Otherwise all that code would've been left in the Sub (which was originally the case).
 
Thats good advice. I shall make the alterations in the application's properties, changing the .NET version from 3.5 down to 2.0.

I have an innate need to always run the latest and greatest software. Unfortunately, not everybody does as I do. Many offices for instance, use very very old software (eg. old operating systems and office applications), with no updates.

Incidentally, I spent about 8-10 hours yesterday, re-writing the code, changing container usage from array lists to generic lists. This was a bit of a pain, but from reading around, it is clear that on 64-bit operating systems, there are major memory usage benefits when it comes to using generic lists, compared to array lists.

Thanks for your help gents.
 
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