Hi Guangda,
Thanks for using Zoom SDK. If you would like to use Custom UI, after setting the Custom UI by calling the setCustomizedMeetingUIEnabled, you might want to call isCustomizedMeetingUIEnabled to double check whether the Custom UI is truly enabled. The Custom UI feature is a paid feature so it is not available for all accounts.
If you do not want to purchase Custom UI feature, one of our demo apps shows a way of implementing a similar outcome of what you are mentioning without using Custom UI.
Hope this helps. Thanks!