学步园

示例1.演示异步获取一个网址的内容，处理后显示在OutPut这一Label上

 1using System;
 2using System.Web;
 3using System.Web.UI;
 4using System.Web.UI.WebControls;
 5using System.Net;
 6using System.IO;
 7using System.Text;
 8using System.Text.RegularExpressions;
 9
10public partial class AsyncPage : System.Web.UI.Page
11{
12    private WebRequest _request;
13
14    void Page_Load (object sender, EventArgs e)
15    {
16        AddOnPreRenderCompleteAsync (
17            new BeginEventHandler(BeginAsyncOperation),
18            new EndEventHandler (EndAsyncOperation)
19        );
20    }
21
22    IAsyncResult BeginAsyncOperation (object sender, EventArgs e, 
23        AsyncCallback cb, object state)
24    {
25        _request = WebRequest.Create("http://msdn.microsoft.com");
26        return _request.BeginGetResponse (cb, state);
27    }
28    void EndAsyncOperation (IAsyncResult ar)
29    {
30        string text;
31        using (WebResponse response = _request.EndGetResponse(ar))
32        {
33            using (StreamReader reader = 
34                new StreamReader(response.GetResponseStream()))
35            {
36                text = reader.ReadToEnd();
37            }
38        }
39
40        Regex regex = new Regex ("href//s*=//s*/"([^/"]*)/"", 
41            RegexOptions.IgnoreCase);
42        MatchCollection matches = regex.Matches(text);
43
44        StringBuilder builder = new StringBuilder(1024);
45        foreach (Match match in matches)
46        {
47            builder.Append (match.Groups[1]);
48            builder.Append("<br/>");
49        }
50
51        Output.Text = builder.ToString ();
52    }
53}
54
55

示例2:演示如何异步从数据库查询数据，并将返回的DataReader绑定到指定控件上

using System;
using System.Data;
using System.Data.SqlClient;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.Configuration;

public partial class AsyncDataBind : System.Web.UI.Page
{
    private SqlConnection _connection;
    private SqlCommand _command;
    private SqlDataReader _reader;


    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            // Hook PreRenderComplete event for data binding
            this.PreRenderComplete += 
                new EventHandler(Page_PreRenderComplete);

            // Register async methods
            AddOnPreRenderCompleteAsync(
                new BeginEventHandler(BeginAsyncOperation),
                new EndEventHandler(EndAsyncOperation)
            );
        }
    }
    IAsyncResult BeginAsyncOperation (object sender, EventArgs e, 
        AsyncCallback cb, object state)
    {
        string connect = WebConfigurationManager.ConnectionStrings
            ["PubsConnectionString"].ConnectionString;
        _connection = new SqlConnection(connect);
        _connection.Open();
        _command = new SqlCommand(
            "Select title_id, title, price FROM titles", _connection);
        return _command.BeginExecuteReader (cb, state);
    }

    void EndAsyncOperation(IAsyncResult ar)
    {
        _reader = _command.EndExecuteReader(ar);
    }

    protected void Page_PreRenderComplete(object sender, EventArgs e)
    {
        Output.DataSource = _reader;
        Output.DataBind();
    }

    public override void Dispose()
    {
        if (_connection != null) _connection.Close();
        base.Dispose();
    }
}

示例3:异步调用WebService

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class AsyncWSInvoke1 : System.Web.UI.Page
{
    private WS.PubsWebService _ws;
    private DataSet _ds;

    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            // Hook PreRenderComplete event for data binding
            this.PreRenderComplete += 
                new EventHandler(Page_PreRenderComplete);

            // Register async methods
            AddOnPreRenderCompleteAsync(
                new BeginEventHandler(BeginAsyncOperation),
                new EndEventHandler(EndAsyncOperation)
            );
        }
    }

    IAsyncResult BeginAsyncOperation (object sender, EventArgs e, 
        AsyncCallback cb, object state)
    {
        _ws = new WS.PubsWebService();
        // Fix up URL for call to local VWD-hosted Web service
        _ws.Url = new Uri(Request.Url, "Pubs.asmx").ToString();
        _ws.UseDefaultCredentials = true;
        return _ws.BeginGetTitles (cb, state);
    }

    void EndAsyncOperation(IAsyncResult ar)
    {
        _ds = _ws.EndGetTitles(ar);
    }

    protected void Page_PreRenderComplete(object sender, EventArgs e)
    {
        Output.DataSource = _ds;
        Output.DataBind();
    }

    public override void Dispose()
    {
        if (_ws != null) _ws.Dispose();
        base.Dispose();
    }
}

示例4:还是异步调用WebService,但换了一种方法

using System;
using System.Data;
using System.Configuration;