Run Time Validation Check Without Page Submit In Oracle Apex

1.Ajax Callback : First we need to create Ajax Callback Process & give a meaningful name of this process. The Process like Bellow........... 

 Begin

    If :P9_QUANTITY is null Then

        htp.prn('Please Input Invoice Quantity.');

    Elsif :P9_QUANTITY =0  Then

        htp.prn('Sorry,Invoice Quantity Should be greater Than 0.');

    Else

        htp.prn('SUCCESS');

    End If;

End;

2. Dynamic Action : Create Dynamic Action in Item Level where we want to execute Validation.

apex.server.process('InvoiceQuantityValidation',
{
   pageItems : '#P9_QUANTITY'
}
,
{
   dataType : 'text', success : function(data)
   {
      if(data != 'SUCCESS') apex.message.alert(data);
   }
}
)