Custom FormDatasource lookup

The following sample demonstrates how to add custom lookup to field on an AX form

 public void lookup(FormControl _formControl, str _filterStr)  
 {  
   SysTableLookup     sysTableLookup = SysTableLookup::newParameters(tablenum(InventItemBarcode), _formControl);  
   Query              query = new Query();  
   QueryBuildDataSource  qbds;  
   ;  
    
   sysTableLookup.addLookupfield(fieldnum(InventItemBarcode, ItemBarcode), true);  
   sysTableLookup.addLookupfield(fieldnum(InventItemBarcode, Description));  
   sysTableLookup.addLookupfield(fieldnum(InventItemBarcode, LIQ_Sell_ItemId));  
   sysTableLookup.addLookupfield(fieldnum(InventItemBarcode, LIQ_UnitId));  
   sysTableLookup.addLookupfield(fieldnum(InventItemBarcode, LIQ_Primary));  
   sysTableLookup.addLookupfield(fieldnum(InventItemBarcode, LIQ_Active));  
    
   qbds = query.addDataSource(tablenum(InventItemBarcode));  
   qbds.addRange(fieldnum(InventItemBarcode, ItemId)).value(queryValue(RCMJournalItemTrans.ItemId));  
    
   sysTableLookup.parmQuery(query);  
   sysTableLookup.performFormLookup();  
 }