How can I use the ovs on my extension fields?

Hi experts,

     I extension the object：FixedAsset, and add a field XMID, below:

          [Extension] businessobject AP.FinancialAccounting.Global:FixedAsset raises myMsg{

                [Label("项目ID")] element XMID:ProjectID;

     I enhance the field XMID to the screen fxacreateqafeco.QA.xuicomponent, but the DisplayType is InputField, I want to use OVS on the field, how can I do ? Thanks.