1 public partial class AsyncSearchForm : Form
 2     {
 3         #region --Delegates--
 4         private delegate void DisplayTimeInfoDelegate(string text);
 5         private delegate void DisplayDataGridViewDelegate(DataTable myTable);
 6         private delegate void DisplayInfoDelegate(string text);
 7         #endregion
 8 
 9         #region --Fields--
10         private SqlConnection mConnection;
11         private Stopwatch mWatch;
12         private DisplayTimeInfoDelegate myTimeDelegate;
13         private DisplayDataGridViewDelegate myDataDelegate;
14         #endregion
15 
16         #region --Constructor--
17         public AsyncSearchForm()
18         {
19             InitializeComponent();
20             mWatch = new Stopwatch();
21             myDataDelegate = new DisplayDataGridViewDelegate(DisplayDataResults);
22             myTimeDelegate = new DisplayTimeInfoDelegate(DisplayTimeResults);
23             button_DoSearch.Click += new EventHandler(Button_DoSearch_Click);
24         }
25         #endregion
26 
27         #region --Event Methods--
28         /// <summary>
29 /// 当点击执行查询时发生
30 /// </summary>
31         private void Button_DoSearch_Click(object sender, EventArgs e)
32         {
33             Application.DoEvents();
34             string connectionString = @"Data Source=127.0.0.1;Integrated Security=SSPI;Database=Northwind;Asynchronous Processing=true";
35             mConnection = new SqlConnection(connectionString);
36             string sqlString = "select * from Orders";
37             SqlCommand command = new SqlCommand(sqlString, mConnection);
38             mConnection.Open();
39             mWatch.Start();
40             AsyncCallback callBack = new AsyncCallback(HandleCallback);//注册回调方法
41 //开始执行异步查询，将Command作为参数传递到回调函数以便执行End操作
42             command.BeginExecuteReader(callBack, command);
43         }
44         #endregion
45 
46         #region --Private Methods--
47         /// <summary>
48 /// 异步查询的回调方法
49 /// </summary>
50 /// <param name="MyResult">异步操作状态</param>
51         private void HandleCallback(IAsyncResult MyResult)
52         {
53             try
54             {
55                 SqlCommand command = (SqlCommand)MyResult.AsyncState;
56                 SqlDataReader reader = command.EndExecuteReader(MyResult);
57                 mWatch.Stop();
58                 string callBackTime = mWatch.ElapsedMilliseconds.ToString() + "毫秒";
59                 DataTable dataTable = new DataTable();
60                 dataTable.Load(reader);                
61                 this.Invoke(myTimeDelegate, callBackTime);                
62                 this.Invoke(myDataDelegate, dataTable);
63             }
64             catch (Exception MyEx)
65             {
66                 this.Invoke(new DisplayInfoDelegate(DisplayTimeResults), String.Format(MyEx.Message));
67             }
68             finally
69             {
70                 if (mConnection != null)
71                 {
72                     mConnection.Close();
73                 }
74             }
75         }
76 
77         /// <summary>
78 /// 在Label上显示信息
79 /// </summary>
80 /// <param name="text"></param>
81         private void DisplayTimeResults(string text)
82         {
83             this.label_Time.Text = label_Time.Text + text;
84         }
85 
86         /// <summary>
87 /// 绑定数据到DataGridView
88 /// </summary>
89 /// <param name="myTable"></param>
90         private void DisplayDataResults(DataTable myTable)
91         {
92             this.dgv_Data.DataSource = myTable;
93         }
94         #endregion
95     }