Steps to Reproduce

1. run the attached zul
2. click "number of rows" button

Current Result

it shows 500 which means Grid creates Row for all item in a model instead of 50 (initial ROD size).

Expected Result

According to our doc: https://www.zkoss.org/wiki/ZK_Developer%27s_Reference/Performance_Tips/Listbox,_Grid_and_Tree_for_Huge_Data/Turn_on_Render_on_Demand

Note that Grid ROD is will not work unless the Grid is configured with a limited view port; i.e. you have to set height or vflex attribute of the Grid or set the Grid to paging mold so the user can see only a portion of the content of the Grid.

So specifying visibleRows should also enable ROD.

Workaround

specify "height"