Hello,
I am trying to use server-side paging in TreeList, and its implementation is a bit ... confusing.
From my understanding, when users are loading grouped data, they expect to have page size to refer to the number of groups per page, not total items.
But even if that number was based on total items, it needs to be stable and not change based on whether the group (tree parent) was expanded.
The weirdest consequence is when users open the last group on the page, they can see that the item expanded, but no items underneath. For a while, I thought it was just hidden behind the pager toolbar.

https://stackblitz.com/edit/react-9fmppn?file=app%2Fmain.jsx
Here is an example for you to try. See how the number of pages is changing when you expand the tree element.
Is there a way to implement my pager to be more user-friendly and less confusing?
Thanks.

Hi Stefan,
Thanks for your reply.
Honestly, it depends on particular data and how a user wants to focus on data.
For example, if we are looking at the list of employees grouped by departments, with pagination showing ten results per page; the most expected behavior is to see the number of pages based on the number of departments (groups), and correspondingly pager info to say "1-10 of 100 departments". That way, the department, when opened, will always show all underlying employees, and never spread across into multiple pages.
However, I can imagine that users might be interested in employee data as much, so we can potentially spread the departments into a couple of pages if needed and base our page number on the number of employees. So, then pager info will say 1-10 of 2000 employees. However, if we need to continue showing employees from the department that started on the previous page, we still have a department tree item on the page to collapse it. Currently, if you have ten items per page and you expanded the parent item on page 1 and went to page 2 to see the child items, you will need to return to the page 1 to collapse the parent.
For the cases above, the main two differences from current tree list behavior are:
 - we do not change the number of pages or totals based on tree expanded items
 - we do show top group element on every page, to give a context and to allow a user to collapse the parent

I hope this makes some sense :)

For now, I was able to get what I need by controlling the Pager component separately and making TreeList not pageable.
Thanks,
Vitaliy.

Hello, Vitaliy,

Thank you for the very detailed information.

Indeed, using a separate Pager is a great option for this case.

Making this built-in has its limitations, as the behavior depends on external factors, and if we make it to cover 1 use case, it will be strange for others. This is why we try to made in to show the pages based on the expanded and visible items directly instead of making assumptions what the user will expect, as this could produce unexpected results for different user groups.

Regards,
Stefan
Progress Telerik