Silverlight DataGrid With CheckBox

When i Check The CheckBox  and Click the Cancel Button The Checked Data

Should Be Updated (i.e.,I Have LeaveStatus DataField In That Already Status

As Stored As "P" When i Click The Cancel Button THe Status Will Be

Updated as "C")

Table Name=LEAVEAPP;
Query=GetCancelLeaveApply;
DatGridName=dgCancellation;
ButtonName=btnCancel;

Am using this in Cancelbuttonclick event
  private void btnCancel_Click(object sender, RoutedEventArgs e)
        {
            int empid = Int32.Parse(WebContext.Current.User.Name);
            EntityQuery query =

objectcontext.GetCancelLeaveApplyQuery();
            LoadOperation loadop = objectcontext.Load(query);
           

objectcontext.Load(objectcontext.GetCancelLeaveApplyQuery()).Completed

+= new EventHandler(Cancellation_Completed);

            objectcontext.SubmitChanges();
          
        }

void Cancellation_Completed(object sender, EventArgs e)
        {
            CheckBox chkbox =

(CheckBox)this.dgCancellation.Columns[0].GetCellContent(this.dgCancellatio

n.SelectedItem);
          
            List tblist;
           tblist =

((System.ServiceModel.DomainServices.Client.LoadOperation

AVEAPP>)(sender)).Entities.ToList();
           foreach (LEAVEAPP lvapp in tblist)
           {
                     if (lvapp.EMPLOYEEID ==

Int32.Parse(WebContext.Current.User.Name))
                         objleaveapp = lvapp;
                }
          
           if (objleaveapp != null)
           {
             
               if ((bool)chkbox.IsChecked)
               {
                   objleaveapp.LV_STATUS = "C ";

               }
               objectcontext.SubmitChanges();
               MessageBox.Show("Done");

           }
        }

LinqQuery is

   public IQueryable GetCancelLeaveApply()
        {
            var qry = from tblleaveapp in this.ObjectContext.LEAVEAPP select

tblleaveapp;
            return qry;
        }