c# – 使用SqlDependency导致不断更新

我从 this MSDN page中提取了一个例子并且几乎逐字地使用了它.运行时代码编译正确,但无论是否实际对返回的数据进行了更改,changeCount都会无限增加.实际发生更改时,dataGridView1会正确反映更改.为什么我的SqlDependency看起来像是在循环中触发,即使显然没有变化？

这是来源：

#region Using directives
using System;
using System.Collections;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Data.SqlClient;
using System.Drawing;
using System.Linq;
using System.Runtime.InteropServices;
using System.Security.Permissions;
using System.Text;
using System.Windows.Forms;
#endregion

namespace PreAllocation_Check
{
    public partial class Form1 : Form
    {
        int           changeCount = 0;
        const string  tableName = "MoxyPosition";
        const string  statusMessage = "Last: {0} - {1} changes.";
        DataSet       dataToWatch = null;
        SqlConnection MoxyConn = null;
        SqlCommand    SQLComm = null;

        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender,EventArgs e)
        {
            if (CanRequestNotifications())
            {
                SqlDependency.Start(GetConnectionString());

                if (MoxyConn == null)
                    MoxyConn = new SqlConnection(GetConnectionString());

                if (SQLComm == null)
                {
                    SQLComm = new SqlCommand(GetSQL(),MoxyConn);

                    SqlParameter prm = new SqlParameter("@Quantity",SqlDbType.Int);
                    prm.Direction = ParameterDirection.Input;
                    prm.DbType = DbType.Int32;
                    prm.Value = 100;
                    SQLComm.Parameters.Add(prm);
                }

                if (dataToWatch == null)
                    dataToWatch = new DataSet();

                GetData();
            }
        }

        private void Form1_FormClosed(object sender,FormClosedEventArgs e)
        {
            SqlDependency.Stop(GetConnectionString());
            if (MoxyConn != null)
                MoxyConn.Close();
        }

        private bool CanRequestNotifications()
        {
            try
            {
                SqlClientPermission SQLPerm = new SqlClientPermission(PermissionState.Unrestricted);
                SQLPerm.Demand();
                return true;
            }
            catch
            {
                return false;
            }
        }

        private string GetConnectionString()
        {
            return "server=***;database=***;user id=***;password=***";
        }

        private void GetData()
        {
            dataToWatch.Clear();
            SQLComm.Notification = null;
            SqlDependency SQLDep = new SqlDependency(SQLComm);
            SQLDep.OnChange += new OnChangeEventHandler(SQLDep_OnChange);

            using (SqlDataAdapter adapter = new SqlDataAdapter(SQLComm))
            {
                adapter.Fill(dataToWatch,tableName);
                dataGridView1.DataSource = dataToWatch;
                dataGridView1.DataMember = tableName;
            }
        }

        private string GetSQL()
        {
            return "SELECT PortID,CONVERT(money,SUM(PreAllocPos),1) AS PreAllocation,SUM(AllocPos),1) AS Allocation,SUM(PreAllocPos) - SUM(AllocPos),1) AS PreLessAlloc " +
                   "FROM MoxyPosition " +
                   "WHERE CONVERT(money,PreAllocPos,1) <> CONVERT(money,AllocPos,1) " +
                   "GROUP BY PortID " +
                   "ORDER BY PortID ASC;";
        }

        void SQLDep_OnChange(object sender,SqlNotificationEventArgs e)
        {
            ISynchronizeInvoke i = (ISynchronizeInvoke)this;

            if (i.InvokeRequired)
            {
                OnChangeEventHandler tempDelegate = new OnChangeEventHandler(SQLDep_OnChange);
                object[] args = { sender,e };
                i.BeginInvoke(tempDelegate,args);
                return;
            }

            SqlDependency SQLDep = (SqlDependency)sender;
            SQLDep.OnChange -= SQLDep_OnChange;

            changeCount++;
            DateTime LastRefresh = System.DateTime.Now;
            label1.Text = String.Format(statusMessage,LastRefresh.TimeOfDay,changeCount);

            GetData();
        }
    }
}

编辑：值得注意的是,我想要运行此数据库的数据库当前没有启用Broker服务,因此要测试我的代码我备份了我的目标数据库并使用新名称恢复它,然后运行ALTER DATABASE my_db_name SET ENABLE_BROKER反对.我的所有测试都在这个备用数据库上,这意味着我是唯一的用户.

Gets a value that indicates whether this notification is generated 
because of an actual change,OR BY THE SUBSCRIPTION.