I want to add the item class on in the Catalog grid in the portal. I want to add custom filters to the screen.
Populating the field with a rowselected or initializing wont work because I need to filter the value. 

I have try adding the field in a extension file but the field keeps giving back 0 as the value, any idea what I could be doing wrong?

namespace SP.Objects.IN
{
  

    public class InventoryLinesExt : PXCacheExtension<InventoryLines>
    {

        // Here i tried adding a new field to link with the current line inventoryID
        #region UsrCustomField
        lPXInt]
        PPXUIField(DisplayName = "Item Class")]
        mPXDefault(typeof(Search<
            InventoryItem.itemClassID,
            Where<InventoryItem.inventoryID, Equal<Current<InventoryLines.inventoryID>>>>))]
        public virtual int UsrItemClass { get; set; }
        public abstract class usrCustomField : PX.Data.BQL.BqlInt.Field<usrCustomField> { }
        #endregion

         // here I was trying to hook into the PXProjection to populate the field

        public abstract class itemClassID : BqlType<IBqlInt, int>.Field<itemClassID>
        {
        }
    }
}