Bug in VFP 9? Adding an object to an array with AddObject.

Bug in VFP 9? Adding an object to an array with AddObject.

• SnowJim

  Sorin,
  From screen shot it looks like you were really using collection class. Is there a reason you're not using Collection.Add().
  
  
  

• lary

  Sorin,
  Does it error if you instead code it as:
  
  this.ItemCount = this.ItemCount + 1
  Dimension this.Item[this.ItemCount]
  
  this.Item[this.ItemCount] = ;
    NewObject(this.ItemClassName, ClassLibNameHere, '', &tInitParameters)
  
  
  

• Daddicool

  I cannot provide reproductibile code because as I said it only errors one in 10s of thousant of calls. The object being added is a non-visual class (based on the "custom" VFP class). Nating fancy with this object, just a few properties on it.
  
  It just happened again so here are more accurate details :
  
  - When it errors, the array element where the object was supposed to be added remains .f. Say the line of code was :
  
  this.addobject(cItem,cLib) where cItem was 'Item[20]'. The array element 20 will still be false but there is an object showing in the debugger on the "this" with the name "Item[20]". I have a screen shot of the debugger but I don't see any picture upload feature here. trying to reference this.item[20] will return .f., not the item[20] rogue object.
  
  

• C Martin

  Since this code is in a class, try trapping for that error and retrying.
  
  local lcOldOnError, llError
  lcOldonError = ON('Error')
  on error llError = .T.
  llError = .T.
  do while llError
     llError = .F.
      && add the object here
  enddo
  on error &lcOldOnError
  
  Another approach:
  
  local llError
  llError = .T.
  do while llError
     llError = .F.
     && add the object here
     if type('array_item_here') <> 'O'
        llError = .T.
     endif
  enddo
  
  You can also do while the array item type is not 'O'.
  
  If you could post the relevant code of your custom class and code you are running to populate this array, we could probably come up with better solutions.
  
  

• digitaladvisor

  We don't use the collection class. This is VFP 6 code where we basically implemented collections using arrays of objects.
  
  

• Dancer

  I see. I tried to get error with a simple code that I ran for 10000 times (each time adding 100 custom objects). It didn't error. Here is the code I used:
  
  

  LOCAL oContainer

  For jx=1 To 10000

  oContainer = Createobject('myContainer')

  Endfor

   

  Define Class myContainer As Container

  ItemCount = 0

  Dimension Item[1]

  Procedure Init

  Local ix

  For ix=1 To 100

  This.ItemCount = This.ItemCount + 1

  Dimension This.Item[this.ItemCount]

  This.AddObject('Item['+Alltrim(Str(This.ItemCount))+']', 'Custom')

  Endfor

  Endproc

  Enddefine

  
  

• skyfire

  Here is a link to the screen shot
  
  http://www.bostonphotographs.com/images/Picture4.jpg
  
  I forgot to mention, so far retrying that line will run just fine.
  
  thank you
  
  Sorin
  
  

• Mark Wilkins

  Hi, I'm Richard. I work with Sorin. I'm not a VFP expert, but he and I have discussed this problem and agree that we don't know how to proceed without significant code re-writing.
  
  Mark asked for some more details on how code is structured. CetinBasoz's myContainer example covers the basics pretty well. The this in Sorin's examples are an instance of a subclass derived from a "base_collection" class, which implements the fundamentals.  There is no overridden AddObject method. This is the basic functionality derived from custom.
  
  What makes this seems like a real bug in VFP(9 ) is the presence of an object member named this.item[1]. Look carefully at the debugger screen shot Sorin showed here:
  

  http://www.bostonphotographs.com/images/Picture4.jpg
  

  this.item[1] is not an array element. And if if you try to refer to it in (e.g.) the command window, you get .F., which is the value of the 1st element in the item array, which is not the object member mysteriously named item[1].
  
  Can any of you propose a way of legitmately creating/referring to/removing an object member named this.item[1], with square bracket in the name If so, we can scrutinize our code to see if we somehow could possibly be doing this (though it is doubtful, as this code is localized in a base class). But otherwise it seems like a VFP bug.
  
  Cheers,
  Richard
  

  
  

• Chiwi

  I don't know if it would error or not but that construct would not work in our code as NewObject or CreateObject will not create the object as a child to the "this" object and there are a milion places where code in one of the array element methods is referencing it's parent.
  
  For example
  
  _screen.AddProperty('aTest[2]')
  _screen.atest[1] = NEWOBJECT('custom')
  _screen.addObject('atest[2]','custom')
  _screen.aTest[1].Parent.name && this will bomb because the object is not a child to the "screen" object.
  _screen.aTest[2].Parent.name && this will work.
  

  
  
  

• Alex Jankowski

  Unfortunately I cannot provide code to reproduce the error. This base class is used throughout our entire system for different and it errors maybe a couple of times a day (among 10/15 users in QA). This however is unacceptable for the production system so I guess deployment will have to be delayed.
  
  I could not find any pattern between the instances where the errors occurs. It seems to be completely random. Someone (offline) suggested that it might be related to us using "Item" (a reserved word since VFP8) for the array name. You think this might have anything to do with it
  
  thank you
  
  Sorin
  
  

• Strakian

  Could you post some sample code that gives us an idea of what kind of object you are adding. For example, is it an object reference to a form that you are adding to the array If you can help us develop some reproducible code or at least code snippets from your app where this is occuring, we can better help you .
  
  

• marvino

  Mike Stewart posted this to ProFox in relation to a similar type of problem:
  
  "Foxpro gets confused about the object name unless you explicitly reference the containing object."
  
  Try
  cItemPlace = "This.Item[" + LTrim(Str(this.ItemCount)) + "]"
  
  Stuart
  
  
  
  
  

• Carrington2

  I do not think the use of "Item" is the problem. For convenience, I have reposted the code you provided in your original message below:
  
  

  this.ItemCount = this.ItemCount + 1
  Dimension this.Item[this.ItemCount]

  Local cItemPlace
  cItemPlace = "Item[" + LTrim(Str(this.ItemCount)) + "]"

  this.AddObject(cItemPlace, this.ItemClassName, &tInitParameters)
  
  Does "THIS" refer to your custom class object If so, then your Custom class has an AddObject method with your own code that adds the object reference to the array property of the custom object. Is this correct If so, what does the code in your AddObject method look like Where is the code listed above located Is there any other code in that method that may help us if you posted it If you can help us create the minimum amount of code that you are using that generates this error, then we can run it thousands of times to see if we can get an error. Or at least see if there is a better solution.

  
  
  

• RyanF

  There is no difference in the syntax of item[1] and item(1) so there is no way to get VFP to distinguish between the two of those. I initially thought the class was entirely custom code where the use of ITEM would not be a problem. I now think otherwise. Since this is a class that seems to be reused, I would think you could make some minor changes that would not cause a massive rewrite of the other code that uses this class. Namely the use of error trapping around where you are calling the "AddObject" method. I proposed in my second reply in this thread. Do you think that might work
  
  
• Bug in VFP 9? Adding an object to an array with AddObject.