in GUI Development by

Good Day to All.
i have 4 vertical lists side by side. they are all connected to same scrollbar.

all my lists are in reverse order meaning when the array containing the items are updated my first array element is shown on last place in the list.

after going all the way down at the list then starting to scroll back up my empty list index starts to fill itself with replications of the single item that was presented on last place. Here how it looks.


This is the top of the list area.


this is the bottom. see how the items in between first items of the second list and last item is empty normally.


after scrolling back upthe info on the last index of the list 2 replicated it self to index 9.       


if i scroll more to bottom and back to top rest of the list will continue to fill itself.                              


after too many scrolling the list will just fill it self with yellow information completely


Thank you all. i can try to post a video or gif if needed



1 Answer

0 votes


if you observe duplicates of an item within the list, please review the implementation of the corresponding onLoadItem slot methods. This method is responsible for loading the list with its contents. 

One possibility is: the onLoadItem method has loaded the same content twice.

Second possibility: the onLoadItem method has ignored the loading of an item. Internally, the list manages a cache with few item objects. When you scroll the list, the objects are reused and re-loaded with new contents. If the method onLoadItem is not correctly implemented, the reused item will retain its old contents.

To investigate such problems more in detail add trace statements to the onLoadItem method. Then you can print contents of local variables evaluated in the onLoadItem method as well as log decisions made there. The trace outputs are printed in the Log window. You can also use the integrated debugger to step through the code.

I hope it helps you further.

Best regards

Paul Banach

Hello Paul. Thanks for the response i am still investigating the issue.
Here is a minute long video of what exactly happens.

google drive link



the video seems to confirm what I have supposed. When the list scrolls, the items are not correctly re-loaded. The content of some items changes suddenly. I think, you have to continue the investigation whether OnLoadItem method does work as expected. Further hints:

1. Does your actual implementation access the items within the list directly? If yes, this should be avoided. Please see also Access list items and views.

2. When the user drags on the scrollbar, how do you scroll the list? The correct approach would be to adjust the ScrollOffset property of the Vertical List object. Is this the case?

Best regards

Paul Banach

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