Steps to Reproduce

run the attachment listbox-in-borderlayout.zul
click the button

change the number of listitems to render in the <foreach> element

Current Result

With increasing number of listitems resizing operations take increasingly longer
Here a few measurements by the Chrome profiler showing the non linear progression

• 10 -> ~230ms
• 20 -> ~700ms
• 30 -> ~1500ms
• 40 -> ~2800ms
• 50 -> ~4500ms

Expected Result

results comparable or better to 8.5.2.1 (this didn't happen in the previous version)

Debug Info

The following changes each improve the situation significantly

• making the button visible in the first cell
• removing the hflex="1" in the second cell
• removing the vflex="1" from the listbox
• replacing the surrounding borderlayout with a simple div

the combination of the conditions causes the performance degradation

nesting multiple borderlayouts multiplies the negative effect

• grid also has the same problem, please check the attached zul

Root Cause

Workaround