private void button1_Click(object sender, EventArgs e)
        {
            SqlConnection conn = new SqlConnection(@"....连接字符串。。");
            ....
.....
            try
            {
                conn.Open();
                SqlTransaction sqltrans = conn.BeginTransaction();

                ....

  数据操作
  ........

                sqltrans.Commit(); 
                MessageBox.Show("Transaction committed");

            }

            catch (System.Data.SqlClient.SqlException ex)
            {
                sqltrans.Rollback();//这个sqltrans上下文中不存在。什么原因 请教
                ....

  .....
            }

            catch (System.Exception ex)
            {
                .......
            }
            finally
            {
                conn.Close();
            }
        }