Вы можете расширить DropDownList и заставить его хранить список объектов в сеансе.
Как это:
DropDownListKeepRef:
using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Collections;
using System.ComponentModel;
using System.Collections.Generic;
namespace Q11456633WebApp
{
/// <summary>
/// Extension of <see cref="DropDownList"/> supporting reference to the
/// object related to the selected line.
/// </summary>
[ValidationProperty("SelectedItem")]
[SupportsEventValidation]
[ToolboxData(
"<{0}:DropDownListKeepRef runat=\"server\"></{0}:DropDownListKeepRef>")]
public class DropDownListKeepRef : DropDownList
{
protected override void PerformDataBinding(System.Collections.IEnumerable dataSource)
{
if (!String.IsNullOrEmpty(this.DataValueField))
{
throw new InvalidOperationException(
"'DataValueField' cant be define in this implementation. This Control use the index of list");
}
this.Items.Clear();
ArrayList list = new ArrayList();
int valueInt = 0;
if (this.FirstNull)
{
list.Add(null);
this.Items.Add(new ListItem(this.FirstNullText, valueInt.ToString()));
valueInt++;
}
foreach (object item in dataSource)
{
String textStr = null;
if (item != null)
{
Object textObj = item.GetType().GetProperty(this.DataTextField).GetValue(item, null);
textStr = textObj != null ? textObj.ToString() : "";
}
else
{
textStr = "";
}
//montando a listagem
list.Add(item);
this.Items.Add(new ListItem(textStr, valueInt.ToString()));
valueInt++;
}
this.listOnSession = list;
}
private bool firstNull = false;
/// <summary>
/// If <c>true</ c> include a first line that will make reference to <c>null</c>,
/// otherwise there will be only the line from the DataSource.
/// </summary>
[DefaultValue(false)]
[Themeable(false)]
public bool FirstNull
{
get
{
return firstNull;
}
set
{
firstNull = value;
}
}
private string firstNullText = "";
/// <summary>
/// Text used if you want a first-line reference to <c>null</c>.
/// </summary>
[DefaultValue("")]
[Themeable(false)]
public virtual string FirstNullText
{
get
{
return firstNullText;
}
set
{
firstNullText = value;
}
}
/// <summary>
/// List that keeps the object instances.
/// </summary>
private IList listOnSession
{
get
{
return this.listOfListsOnSession[this.UniqueID + "_listOnSession"];
}
set
{
this.listOfListsOnSession[this.UniqueID + "_listOnSession"] = value;
}
}
#region to avoid memory overload
private string currentPage
{
get
{
return (string)HttpContext.Current.Session["DdlkrCurrentPage"];
}
set
{
HttpContext.Current.Session["DdlkrCurrentPage"] = value;
}
}
/// <summary>
/// Every time you change page, lists for the previous page will be
/// discarded from memory.
/// </summary>
private IDictionary<String, IList> listOfListsOnSession
{
get
{
if (currentPage != this.Page.Request.ApplicationPath)
{
currentPage = this.Page.Request.ApplicationPath;
HttpContext.Current.Session["DdlkrListOfListsOnSession"] = new Dictionary<String, IList>();
}
if (HttpContext.Current.Session["DdlkrListOfListsOnSession"] == null)
{
HttpContext.Current.Session["DdlkrListOfListsOnSession"] = new Dictionary<String, IList>();
}
return (IDictionary<String, IList>)HttpContext.Current.Session["DdlkrListOfListsOnSession"];
}
}
#endregion
public Object SelectedObject
{
get
{
if (this.SelectedIndex > 0 && this.listOnSession.Count > this.SelectedIndex)
return this.listOnSession[this.SelectedIndex];
else
return null;
}
set
{
if (!this.listOnSession.Contains(value))
{
throw new IndexOutOfRangeException(
"Objeto nao contido neste 'DropDownListKeepRef': " +
value != null ? value.ToString() : "<null>");
}
else
{
this.SelectedIndex = this.listOnSession.IndexOf(value);
}
}
}
/// <summary>
/// List of related objects.
/// </summary>
public IList Objects
{
get
{
return new ArrayList(this.listOnSession);
}
}
[System.Security.Permissions.PermissionSet(System.Security.Permissions.SecurityAction.Demand, Name = "FullTrust")]
protected override void LoadViewState(object savedState)
{
object[] totalState = null;
if (savedState != null)
{
totalState = (object[])savedState;
if (totalState.Length != 3)
{
throw new InvalidOperationException("View State Invalida!");
}
// Load base state.
int i = 0;
base.LoadViewState(totalState[i++]);
// Load extra information specific to this control.
this.firstNull = (bool)totalState[i++];
this.firstNullText = (String)totalState[i++];
}
}
[System.Security.Permissions.PermissionSet(System.Security.Permissions.SecurityAction.Demand, Name = "FullTrust")]
protected override object SaveViewState()
{
object baseState = base.SaveViewState();
object[] totalState = new object[3];
int i = 0;
totalState[i++] = baseState;
totalState[i++] = this.firstNull;
totalState[i++] = this.firstNullText;
return totalState;
}
}
}
Default.aspx:
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="Q11456633WebApp._Default" %>
<%@ Register Assembly="Q11456633WebApp" Namespace="Q11456633WebApp" TagPrefix="cc1" %>
<!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>Untitled Page</title>
</head>
<body>
<form id="form1" runat="server">
<div>
<cc1:DropDownListKeepRef ID="ListofDatesDdlkr" runat="server" AutoPostBack="True" DataTextField="Date" OnSelectedIndexChanged="ListofDatesDdlkr_SelectedIndexChanged">
</cc1:DropDownListKeepRef> </div>
</form>
</body>
</html>
Default.aspx.cs:
using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
namespace Q11456633WebApp
{
public partial class _Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
if (!this.IsPostBack)
{
this.ListofDatesDdlkr.DataSource = this.ListOfDate;
this.ListofDatesDdlkr.DataBind();
}
}
private DateTime[] ListOfDate
{
get
{
return new DateTime[]
{
new DateTime(2012, 7, 1),
new DateTime(2012, 7, 2),
new DateTime(2012, 7, 3),
new DateTime(2012, 7, 4),
new DateTime(2012, 7, 5),
};
}
}
protected void ListofDatesDdlkr_SelectedIndexChanged(object sender, EventArgs e)
{
this.ClientScript.RegisterStartupScript(
this.GetType(),
"show_type",
String.Format(
"alert('Type of SelectedObject:{0}')",
this
.ListofDatesDdlkr
.SelectedObject
.GetType()
.FullName),
true);
}
}
}
Решение с полным кодом: Q11456633WebApp.7z
Веб-сайт без гражданства, несмотря на магию ASP .NET. Все, что вам нужно, это выбранное свойство «Значение». Во время post back вы должны иметь возможность найти объект на основе значения. Так оно и должно работать. – Yuck