MSDN官方的ASP.Net异步页面的经典示例代码

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;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class AsyncWSInvoke2 : 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);

            // Call the Web service asynchronously
            _ws = new WS.PubsWebService();
            _ws.GetTitlesCompleted += new 
                WS.GetTitlesCompletedEventHandler(GetTitlesCompleted);
            _ws.Url = new Uri(Request.Url, "Pubs.asmx").ToString();
            _ws.UseDefaultCredentials = true;
            _ws.GetTitlesAsync();
        }
    }

    void GetTitlesCompleted(Object source, 
        WS.GetTitlesCompletedEventArgs e)
    {
        _ds = e.Result;
    }

    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5：跟示例1差不多，但是加了TimeOut处理

using System;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Net;
using System.IO;
using System.Text;
using System.Text.RegularExpressions;

public partial class AsyncPageTask : System.Web.UI.Page
{
    private WebRequest _request;

    protected void Page_Load(object sender, EventArgs e)
    {
        PageAsyncTask task = new PageAsyncTask(
            new BeginEventHandler(BeginAsyncOperation),
            new EndEventHandler(EndAsyncOperation),
            new EndEventHandler(TimeoutAsyncOperation),
            null
        );
        RegisterAsyncTask(task);
    }

    IAsyncResult BeginAsyncOperation(object sender, EventArgs e, 
        AsyncCallback cb, object state)
    {
        _request = WebRequest.Create("http://msdn.microsoft.com");
        return _request.BeginGetResponse(cb, state);
    }

    void EndAsyncOperation(IAsyncResult ar)
    {
        string text;
        using (WebResponse response = _request.EndGetResponse(ar))
        {
            using (StreamReader reader = 
                new StreamReader(response.GetResponseStream()))
            {
                text = reader.ReadToEnd();
            }
        }

        Regex regex = new Regex("href\\s*=\\s*\"([^\"]*)\"", 
            RegexOptions.IgnoreCase);
        MatchCollection matches = regex.Matches(text);

        StringBuilder builder = new StringBuilder(1024);
        foreach (Match match in matches)
        {
            builder.Append(match.Groups[1]);
            builder.Append("<br/>");
        }

        Output.Text = builder.ToString();
    }

    void TimeoutAsyncOperation(IAsyncResult ar)
    {
        Output.Text = "Data temporarily unavailable";
    }
}