Mandatory Check on Drop Down Fields

Hi,

  I am relatively new with the Web Dynpro Development and during one of the developments, i have a requirement of setting Dropdown by Index Field Mandatory. For your information, The cardinality of the field is set to 0....n and i have tried the following options with no effect.

1. Set State property to "Required" and using cl_wd_dynamic_tool=>check_mandatory_attr_on_view

Could you please guide me or provide me with a sample code as to how to make a Dropdown Field have a mandatory check in Web Dynpro

Thanx....