In Gridview dynamic text boxes textchange event does not work properly

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C#5.0

i have a gridview in which i have two text boxes and one button ,when user click on button a new row with two textboxes is added, i want to use text change event in 1st textbox, and at the end pass a value to 2nd text box,problem is that ,value does not show up in the textbox

protected void txtCode_TextChanged(object sender, EventArgs e)
       {
          GridViewRow currentRow =(GridViewRow)((TextBox)sender).Parent.Parent;
          TextBox txt = (TextBox)currentRow.FindControl("txtCode");
          TextBox txtfine = (TextBox)currentRow.FindControl("txtFine");
             Int32 count =Convert.ToInt32( txt.Text);
               var chkradio = rblQualification.SelectedValue;
               byte chkRadio = SafeConvert.ToByte(chkradio);
               var vehiclecategory = _service.GetAllVehicleCategory().Where(x => x.ID == chkRadio).FirstOrDefault();
               var vehicletype = vehiclecategory.VehicleType_Id;
               var pntytype = _service.GetAllVehiclePenaltyType().Where(x => x.ID == SafeConvert.ToByte(count)).Count();
               var plntyfee = _service.GetAllVehiclePenaltiesFee().Where(x => x.VehicleTypeID == vehicletype && x.VehiclePenaltyTypeID == vehicletype).FirstOrDefault();
            txtfine.Text = plntyfee.Fee.ToString();

       }