Web 服务在ASP.NET AJAX客户端回调中的应用

1、创建Web服务

添加Web服务，生成TerritoriesService.asmx和TerritoriesService.cs文件。

asmx很简单，只有一行WebService指令。cs源文件如下，包括Web方法，public List<Territory> GetTerritoriesInRegion(int regionID)：根据regionID的值，查询Northwind中的表Territories，获取TerritoryID和TerritoryDescription内容，返回List<Territory>。

View Code

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Services;
using System.Data.SqlClient;
using System.Data;

/// <summary>
/// Summary description for TerritoriesService
/// </summary>
[WebService(Namespace = "http://tempuri.org/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
// To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line. 
[System.Web.Script.Services.ScriptService]
public class TerritoriesService : System.Web.Services.WebService {

    public TerritoriesService () {

        //Uncomment the following line if using designed components 
        //InitializeComponent(); 
    }

    [WebMethod]

    public List<Territory> GetTerritoriesInRegion(int regionID)
    {
        SqlConnection con = new SqlConnection(
          System.Configuration.ConfigurationManager.ConnectionStrings["Northwind"].ConnectionString);
        SqlCommand cmd = new SqlCommand(
            "SELECT * FROM Territories WHERE RegionID=@RegionID", con);
        cmd.Parameters.Add(new SqlParameter("@RegionID", SqlDbType.Int, 4));
        cmd.Parameters["@RegionID"].Value = regionID;

        List<Territory> territories = new List<Territory>();
        try
        {
            con.Open();
            SqlDataReader reader = cmd.ExecuteReader();

            while (reader.Read())
            {
                territories.Add(new Territory(
                  reader["TerritoryID"].ToString(),
                  reader["TerritoryDescription"].ToString()));
            }
            reader.Close();
        }
        catch (SqlException err)
        {
            // Mask errors.
            throw new ApplicationException("Data error.");
        }
        finally
        {
            con.Close();
        }
        return territories;
    }
    
}

public class Territory
{
    public string ID;
    public string Description;

    public Territory(string id, string description)
    {
        this.ID = id;
        this.Description = description;
    }

    public Territory() { }
}

2、创建Web Form，WebServiceCallback，调用Web 服务，该Web表单中有两个DropDownList，第一个列表获取Northwind数据库中表Region的内容，第二个表中显示RegionID对应的territory信息。

第一个列表中通过onchange特性与客户端javascript函数onChange="GetTerritories(this.value)来触发事件，使用web服务来写触发事件，对执行完web方法后返回的值，通过OnRequestComplete(result)将返回值绑定到第二个dropdownlist中。

注意在aspx文件的开头加上 EnableEventValidation="false"。

aspx的内容如下：

View Code

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="WebServiceCallback.aspx.cs" Inherits="WebServiceCallback" EnableEventValidation="false" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
    <script type="text/javascript">
 
 function GetTerritories(regionID)
 {
    TerritoriesService.GetTerritoriesInRegion(regionID, 
      OnRequestComplete, OnError);
 }
 
 function OnRequestComplete(result)
 {
     var lstTerritories = document.getElementById("lstTerritories");
     lstTerritories.innerHTML = "";
     
     for (var n = 0; n < result.length; n++)
     {
         var option = document.createElement("option");
         option.value = result[n].ID;
         option.innerHTML = result[n].Description;
         lstTerritories.appendChild(option);
      }
  }

 function OnTimeout(result)
 {
     var lbl = document.getElementById("lblInfo");
     lbl.innerHTML = "<b>Request timed out.</b>";
 } 
 
 function OnError(result)
 {
     var lbl = document.getElementById("lblInfo");
     lbl.innerHTML = "<b>" + result.get_message() + "</b>";

     // Can also use this code.
     //lbl.innerHTML += result.get_stackTrace();
 } 
</script>
</head>
<body>
    <form id="form1" runat="server">
        <asp:ScriptManager ID="ScriptManager1" runat="server">
            <Services>
                <asp:ServiceReference Path="~/TerritoriesService.asmx"  />
            </Services>
        </asp:ScriptManager>
        
      <div style="font-family:Verdana;font-size:small ">
        Choose a Region, and then a Territory:<br />
        <br />
        <asp:DropDownList ID="lstRegions" Runat="server" Width="210px" DataSourceID="sourceRegions" DataTextField="RegionDescription" DataValueField="RegionID" onChange="GetTerritories(this.value);">
        </asp:DropDownList>
        <asp:DropDownList ID="lstTerritories" Runat="server" Width="275px">
        </asp:DropDownList><br />
        <br />
        <br />
        <asp:Button ID="cmdOK" Runat="server" Text="OK" Width="50px" OnClick="cmdOK_Click"  /><br />
        <br />
        <asp:Label ID="lblInfo" runat="server"></asp:Label>
        <asp:SqlDataSource ID="sourceRegions" runat="server" ProviderName="System.Data.SqlClient" ConnectionString="<%$ ConnectionStrings:Northwind %>" SelectCommand="SELECT 0 As RegionID, '' AS RegionDescription UNION SELECT RegionID, RegionDescription FROM Region" ></asp:SqlDataSource>
    </div>
    </form>
</body>
</html>

aspx.cs内容很少，只是点击ok按钮后，显示territory的id。

aspx.cs View Code

public partial class WebServiceCallback : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {

    }

    protected void cmdOK_Click(object sender, EventArgs e)
    {
        lblInfo.Text = "You selected territory ID #" + Request.Form["lstTerritories"];

        // Reset the region list box (because the territory list box will be empty).
        lstRegions.SelectedIndex = 0;
    }
}

运行该程序，初始界面如下：

运行结果如下：