Progress® KendoReact Feedback Portal
Back to Feed
Request a Feature Report a Bug
Need More Info
Last Updated: 21 Nov 2025 13:08 by ADMIN
Andrei
Created on: 09 Oct 2025 11:46
Category: KendoReact
Type: Bug Report
0
Error when resizing the container in the treelist
We use "@progress/kendo-react-treelist": "^5.10.1" in our project. Trees are usually placed in flexible containers, and users can reduce their size to 0. At this point, we get an error when calling the tableRowsVirtualization function. I have attached a screenshot at the moment of debugging. You can see that the values of items[0] and lastItem are undefined when the container size approaches 0. I didn't prepare an example to reproduce the error, because I think it's pretty clear that an error occurs here. So the questions are: if this is a bug, is it fixed in the new versions of the package? If there is a possible error on our part or it has not been fixed in the new versions, then what should we do to solve the problem? Thanks
Attached Files:
10 comments
ADMIN
Filip
Posted on: 21 Nov 2025 13:08

Hello, Andrei,

You are absolutely correct that such edits would need to be made in every component using the TreeList, and I agree that this is not ideal. While the TreeList component does not provide a built-in mechanism to transfer configuration through a global context at the root level, a similar result can be achieved by creating a custom React Context for shared TreeList styles or properties. The provider can then be placed near the root of the application, and the context consumed inside a TreeList wrapper component.

I modified the previously sent example with this approach. While this isn’t ideal, I hope it still proves useful and helps avoid some of the hassle with having a lot of TreeList components. I also tried to find a global solution with CSS which would be easier, however this approach causes issues for the virtual scroll and did not yield good results.

Regards,
Filip
Progress Telerik

Love the Telerik and Kendo UI products and believe more people should try them? Invite a fellow developer to become a Progress customer and each of you can get a $50 Amazon gift voucher.

Attached Files:
Andrei
Posted on: 14 Nov 2025 14:48
Hello, Philip! Thanks for the suggested solution. The problem remains that such edits will have to be made in every component using the TreeList. This means dozens of changes for our project, and it will also have to be applied to new TreeList components. Perhaps there is a solution with, for example, transferring the context to the root of the application (such as CalendarPropsContext) or the ability to globally set the height using css or something else? Thanks
ADMIN
Filip
Posted on: 13 Nov 2025 10:41

Hi, Andrei,

After further inspection a possible workaround we can suggest is to set the minimum height so the TreeList always has enough space to render, preventing both the visual disappearance and the zero values. This way even if the slider goes to zero, the TreeList will never collapse to an unusable size. I’ve attached the previously sent project, updated with this approach.

Please let me know in case the issue still persists on your end and I will gladly assist further.

Regards,
Filip
Progress Telerik

Love the Telerik and Kendo UI products and believe more people should try them? Invite a fellow developer to become a Progress customer and each of you can get a $50 Amazon gift voucher.

Attached Files:
ADMIN
Filip
Posted on: 07 Nov 2025 16:18

Hi, Andrei,

Thank you for the provided video. Following the steps I was able to reproduce the described issue. I tried different custom implementations in order to resolve it, however none of them gave a satisfying result. I will need more time in order to sync with the dev team for a possible solution, I will get back to you once I have more feedback on this matter.

Thank you in advance for your patience.

Regards,
Filip
Progress Telerik

Your perspective matters! Join other professionals in the State of Designer-Developer Collaboration 2025: Workflows, Trends and AI survey to share how AI and new workflows are impacting collaboration, and be among the first to see the key findings.
Start the 2025 Survey
Andrei
Posted on: 03 Nov 2025 06:27
Hi, Filip, I don't see in your screenshot that the problem is, you're trying to reproduce the problem correctly, so I've attached a video file where you can see the order of actions as well as the state of variables in the debugger. You can also see that the tree is really disappearing. Regarding your suggestion to upgrade the package to a new version, we cannot afford it, as this will entail the need to update other peer-to-peer versions of telerik packages, which will lead to a cascade of changes in the project. therefore, we really need some kind of solution. thank you!
Attached Files:
ADMIN
Filip
Posted on: 30 Oct 2025 08:25

Hi, Andrei,

Thank you for the sent project. I ran it locally and debugged it after I reduced the container height to zero, however the item was not undefined as seen in the screenshot. I have attached the result from the debugging here:

Can you please confirm if I’m following the correct steps (specifically, resizing the container to zero)? I reviewed our closed issues to check whether this might have been a bug in an older version that was later fixed, but I couldn’t find any responses. I suggest upgrading to the latest version (12.2.0), as many improvements have been made, and the issue may already be resolved in recent releases.

Regards,
Filip
Progress Telerik

Your perspective matters! Join other professionals in the State of Designer-Developer Collaboration 2025: Workflows, Trends and AI survey to share how AI and new workflows are impacting collaboration, and be among the first to see the key findings.
Start the 2025 Survey
Andrei
Posted on: 23 Oct 2025 08:59
Hi, Fillip! thanks for the prepared example. the attachment contains an archive of the project with the possibility of reproducing the error. the problem began to recur after adding virtual scrolling. to do this, I set the scrollable="virtual" and height properties in the style property according to how it is described on the website in the section on virtual scrolling for the TreeList component. I also attached a screenshot again where you can see that lastItem takes the undefined value, which subsequently causes an error. thanks
Attached Files:
ADMIN
Filip
Posted on: 22 Oct 2025 18:33

Hi, Andrei,

It seems that I have attached the wrong project, please accept my apologies for the oversight. I have attached the react project that I tested in which the TreeList is placed inside a flexible container, I have attached it to this ticket. If possible can you please configure it so that it matches your scenario and the issue reproduces? 

Please accept my apologies for the oversight earlier once again.

Regards,
Filip
Progress Telerik

Your perspective matters! Join other professionals in the State of Designer-Developer Collaboration 2025: Workflows, Trends and AI survey to share how AI and new workflows are impacting collaboration, and be among the first to see the key findings.
Start the 2025 Survey
Attached Files:
Andrei
Posted on: 17 Oct 2025 13:50
I just want to clarify if I was understood correctly. we are using "@progress/kendo-react-treelist": "^5.10.1". the package for React, but I received an example for Vue in the attachment. just in case, I want to clarify whether you have tested the React package?
ADMIN
Filip
Posted on: 16 Oct 2025 08:34

Hi, Andrei,

Thank you for the provided screenshot. I went through our public issues and tickets in order to see if someone else had reported the same error, however it seems that this is the first report so far. I tested the TreeList component with both version 5.10.1 and the latest one (12.0.2) in order to reproduce it, however I was not able to. 

I agree that there is an issue based on the screenshot, however we will need to reproduce it locally in order to determine if it's a bug on our end or due to the configuration. I have attached the test project to this ticket. If possible can you please modify it so that the issue reproduces? This will enable me to investigate further if this is a bug and if upgrading to a newer version would resolve it.

Regards,
Filip
Progress Telerik

Your perspective matters! Join other professionals in the State of Designer-Developer Collaboration 2025: Workflows, Trends and AI survey to share how AI and new workflows are impacting collaboration, and be among the first to see the key findings.
Start the 2025 Survey
Attached Files:
Create an account Log In
View
Type
Status
Category