ADO.NET 2.0 数据异步处理改善用户体验

  //// obtain connection strings from configuration files or
            //// similar facility
            //// NOTE: these connection strings have to include "async=true", for
            //// example: 
            //// "server=myserver;database=mydb;integrated security=true;async=true"
             // string connstrAccouting = GetConnString("accounting");
             // string connstrHR = GetConnString("humanresources");
             //// define two connection objects, one for each database
             // using (SqlConnection connAcc = new SqlConnection(connstrAccounting))
             // using (SqlConnection connHumanRes = new SqlConnection(connstrHR))
             // {
             //      //  open the first connection
             //     connAcc.Open();
             //      //  start the execution of the first query contained in the
             //      //  "employee_info" stored-procedure
             //     SqlCommand cmdAcc = new SqlCommand("employee_info", connAcc);
             //     cmdAcc.CommandType = CommandType.StoredProcedure;
             //     cmdAcc.Parameters.AddWithValue("@empl_id", employee_id);
             //     IAsyncResult arAcc = cmdAcc.BeginExecuteReader();
             //      //  at this point, the "employee_info" stored-proc is executing on
             //      //  the server, and this thread is running at the same time
             //      //  now open the second connection
             //     connHumanRes.Open();
             //      //  start the execution of the second stored-proc against
             //      //  the human-resources server
             //     SqlCommand cmdHumanRes = new SqlCommand("employee_hrinfo",
             //                                             connHumanRes);
             //     cmdHumanRes.Parameters.AddWithValue("@empl_id", employee_id);
             //     IAsyncResult arHumanRes = cmdHumanRes.BeginExecuteReader();
             //      //  now both queries are running at the same time
             //      //  at this point; more work can be done from this thread, or we
             //      //  can simply wait until both commands finish - in our case we'll
             //      //  wait
             //     SqlDataReader drAcc = cmdAcc.EndExecuteReader(arAcc);
             //     SqlDataReader drHumanRes = cmdHumanRes.EndExecuteReader(arHumanRes);
             //      //  now we can render the results, for example, bind the readers to an ASP.NET
             //      //  web control, or scan the reader and draw the information in a 
             //      //  WebForms form.
             // }

             string  custid  =   " ALFKI " ;
             string  orderid  =   " 10643 " ;

             //  NOTE: connection strings denoted by "connstring" have to include 
             //  "async=true", for example: 
             string  connstring  =   " server=(local);database=northwind;integrated security=true;async=true " ;
             //  we'll use three connections for this
             using  (SqlConnection c1  =   new  SqlConnection(connstring))
             using  (SqlConnection c2  =   new  SqlConnection(connstring))
             using  (SqlConnection c3  =   new  SqlConnection(connstring))
             {
                // get customer info
                c1.Open();
                SqlCommand cmd1 = new SqlCommand(
                  "SELECT CustomerID, CompanyName, ContactName FROM Customers WHERE CustomerID=@id", c1);
                cmd1.Parameters.Add("@id", SqlDbType.Char, 5).Value = custid;
                IAsyncResult arCustomer = cmd1.BeginExecuteReader();
                // get orders
                c2.Open();
                SqlCommand cmd2 = new SqlCommand("SELECT * FROM Orders WHERE CustomerID=@id", c2);
                cmd2.Parameters.Add("@id", SqlDbType.Char, 5).Value = custid;
                IAsyncResult arOrders = cmd2.BeginExecuteReader();
                // get order detail if user picked an order
                IAsyncResult arDetails = null;
                SqlCommand cmd3 = null;
                if (null != orderid)
                {
                    c3.Open();
                    cmd3 = new SqlCommand("SELECT * FROM [Order Details] WHERE OrderID=@id", c3);
                    cmd3.Parameters.Add("@id", SqlDbType.Int).Value = int.Parse(orderid);
                    arDetails = cmd3.BeginExecuteReader();
                }
                // build the wait handle array for WaitForMultipleObjects
                WaitHandle[] handles = new WaitHandle[null == arDetails ? 2 : 3];
                handles[0] = arCustomer.AsyncWaitHandle;
                handles[1] = arOrders.AsyncWaitHandle;
                if (null != arDetails)
                    handles[2] = arDetails.AsyncWaitHandle;
                // wait for commands to complete and render page controls as we 
                // get data back
                SqlDataReader r;
                DataTable dt;
                for (int results = (null == arDetails) ? 1 : 0; results < 3; results++)
                {
                    // wait for any handle, then process results as they come
                    int index = WaitHandle.WaitAny(handles, 5000, false); // 5 secs
                    if (WaitHandle.WaitTimeout == index)
                        throw new Exception("Timeout");
                    switch (index)
                    {
                        case 0: // customer query is ready
                            r = cmd1.EndExecuteReader(arCustomer);
                            if (!r.Read())
                                continue;
                            lblCustomerID.Text = r.GetString(0);
                            lblCompanyName.Text = r.GetString(1);
                            lblContact.Text = r.GetString(2);
                            r.Close();
                            break;
                        case 1: // orders query is ready
                            r = cmd2.EndExecuteReader(arOrders);
                            dt = new DataTable();
                            dt.Load(r);
                            dgOrders.DataSource = dt; // data-bind to the orders grid
                            dgOrders.Refresh();
                            r.Close();
                            break;
                        case 2: // details query is ready
                            r = cmd3.EndExecuteReader(arDetails);
                            dt = new DataTable();
                            dt.Load(r);
                            dgDetails.DataSource = dt; // data-bind to the details grid
                            dgDetails.Refresh();
                            r.Close();
                            break;

                    }
                }
            }

本文转自高海东博客园博客，原文链接：http://www.cnblogs.com/ghd258/archive/2005/10/30/264839.html，如需转载请自行联系原作者