Mobile App,the insert sql statement inserts more then one row!!!!

hello all,

I am developing a mobile app and i have to insert some values from the txtbox to dhe database table when enter key is pressed.but the sql command inserts more then one row,until i add a new value to the txt box.i think the problem is at the connection.Close();where should i close it,or should i make any if checks??Please help!

Thanks in advance.
Here some part of code:

string _connString = String.Format(System.Globalization.CultureInfo.InvariantCulture,
           @"Data Source = {0}\SQL_CE.sdf", Path.GetDirectoryName(System.Reflection.Assembly.GetExecutingAssembly().GetName().CodeBase));
           SqlCeConnection _connection = new SqlCeConnection(_connString);

           if (e.KeyChar == (char)13)
           {

               _connection.Open();

               SqlCeCommand desc_command = new SqlCeCommand("select description from Items where barcode=@barcode;", _connection);
               desc_command.Parameters.AddWithValue("@barcode", txt_barcode.Text);
               SqlCeDataReader rdr = desc_command.ExecuteReader();
               if (rdr.Read())
               {
                   txt_description.Text = rdr.GetString(0);
               }
               else
               {
                   txt_description.Text = "-----";
               }

               SqlCeCommand _addcommand = new SqlCeCommand("insert into Inventory values(@barcode,@amount);", _connection);
               _addcommand.Parameters.AddWithValue("@barcode", txt_barcode.Text);
               _addcommand.Parameters.AddWithValue("@amount", txt_amount.Text);
               _addcommand.ExecuteNonQuery();
               txt_barcode.Text = "";

               _connection.Close();
           };

Tags: C#, .NET, Visual Studio, SQL Server CE, SQL Server