When using RadTreeList columns there are several resize modes available for you to pick.
I guess you are using the first ResizeMode we support – “NoScroll” (the default one for the demo). In case you select NoScroll mode and decide to resize a column in the TreeList, the size of the other columns will be changed in order for the TreeList to keep its original width. This is expected behavior and is explained in the Description
section of the demo. Here is a short quote:
"- NoScroll (this is the default value) - No changes in the width of the TreeList. The resized column changes width - while the other columns are squeezed at the two ends."
As a summary - when in NoScroll mode, in order to size the columns properly without breaking the TreeList layout, RadTreeList automatically clears the predefined width of the columns that are on the right of the resized column. In case you want to have columns with fixed sizes you should pick one of the other resize modes available for the TreeList: AllowScroll or ResizeTreeList
Here is a link
to our online documentation article where you can explore the various column resize methods and restrictions.
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