How to maintain DataList item index across Postbacks? - asp.net

Question

I'm trying to retain the index of the Datalist item on page reload. I'm trying to do this by storing the index into a Session and then setting the index of DataList object equals to the Session. Here's the HTML code:
<asp:DataList ID="MyList" Width="100%" RepeatDirection="Vertical" runat="server"
OnItemDataBound="MyList_ItemDataBound" OnItemCommand="MyList_ItemCommand">
<ItemTemplate>
<table class="table">
<tr>
<td style="width: 5%;">
<asp:Label ID="lbl_id" runat="server" Text='<%# Eval("id") %>' Visible="false" />
<asp:Label ID="lbl_isread" runat="server" Text='<%# Eval("isread") %>' Visible="false" />
<input type="checkbox" id="chk_vd" runat="server" class="chkitem" />
</td>
<td style="width: 15%;">
<asp:HyperLink ID="usr" runat="server" Text='<%# Eval("from") %>' />
</td>
<td style="width: 62%;">
<asp:LinkButton ID="sub" Text='<%# Eval("subject") %>' CommandName="select" runat="server"></asp:LinkButton>
</td>
<td style="width: 18%;">
<asp:Label ID="dt" runat="server" Text='<%# Eval("Date_Added") %>' />
</td>
</tr>
</table>
</ItemTemplate>
<SelectedItemTemplate>
<table class="table">
<tr>
<td style="width: 5%;">
<asp:Label ID="lbl_id" runat="server" Text='<%# Eval("id") %>' Visible="false" />
<asp:Label ID="lbl_isread" runat="server" Text='<%# Eval("isread") %>' Visible="false" />
<asp:Label ID="lbl_messagetype" runat="server" Text='<%# Eval("messagetype") %>'
Visible="false" />
<asp:Label ID="lbl_groupid" runat="server" Text='<%# Eval("groupid") %>' Visible="false" />
<asp:Label ID="lbl_content_id" runat="server" Text='<%# Eval("content_id") %>' Visible="false" />
<asp:Label ID="lbl_sendertype" runat="server" Text='<%# Eval("sendertype") %>' Visible="false" />
<input type="checkbox" id="chk_vd" runat="server" class="chkitem" />
</td>
<td style="padding: 5px; text-align: left; vertical-align: top; width: 15%;">
<uc1:avator ID="avt" runat="server" UserName='<%# Eval("from") %>' PhotoName="" Width="65"
Height="65" />
<br />
<asp:HyperLink ID="usr" runat="server" Text='<%# Eval("from") %>' />
</td>
<td style="padding: 5px; text-align: left; vertical-align: top; width: 62%;">
<div class="item_pad_4">
<h3 id="s_sub" runat="server">
<%# Eval("subject") %>
</h3>
</div>
<asp:Label ID="msg" runat="server" Text='<%# Eval("body") %>'></asp:Label>
<div class="bx_br_tp item_pad_4">
<div class="btn-group" id="<%# Eval("id") %>">
<asp:LinkButton ID="a" CssClass="btn btn-primary btn-xs" runat="server" />
<asp:LinkButton ID="r" CssClass="btn btn-primary btn-xs" runat="server" />
<%-- <asp:LinkButton ID="lnk_spam" CssClass="btn btn-primary btn-xs" runat="server"
Text="spam" CommandName="spam"></asp:LinkButton>--%>
</div>
</div>
</td>
<td style="padding: 5px; text-align: left; vertical-align: top; width: 18%;">
<asp:Label ID="dt" runat="server" Text='<%# Eval("Date_Added") %>' />
</td>
</tr>
</table>
</SelectedItemTemplate>
</asp:DataList>
On the server side, I'm trying to restore the index of the DataList item as follows:
if (!Page.IsPostBack)
{
if (Session["datalist"] != null)
{
((DataList)Session["datalist"]).SelectedIndex = (int)Session["index"];
}
Here's the function which does data binding :
protected void MyList_ItemCommand(object source, DataListCommandEventArgs e)
{
Session["datalist"] = source;
string cmd = ((LinkButton)e.CommandSource).CommandName;
long messageid = long.Parse(((Label)e.Item.FindControl("lbl_id")).Text);
string username = ((HyperLink)e.Item.FindControl("usr")).Text;
// approve / ignore action related values
long content_id = 0;
long groupid = 0;
int messagetype = 0;
int index = e.Item.ItemIndex;
Session["index"] = index;
index = (int)Session["index"];
switch (cmd)
{
case "select":
((DataList)source).SelectedIndex = e.Item.ItemIndex;
int isread = int.Parse(((Label)e.Item.FindControl("lbl_isread")).Text);
// mark message as read it its unread message
if (isread == 0)
{
isread = 1; // message is read
MailBoxBLL.Update_isRead(messageid, isread, Page.User.Identity.Name);
}
string _cache = "usr_msg_cnt_" + UserName;
if (HttpContext.Current.Cache[_cache] != null)
{
Cache.Remove(_cache);
}
break;
This doesn't work and Datalist item does not get selected when the page reloads. How can I make it work?
Any help is appreciated.

Answer 1

Add this directly in Page Load:-
protected void Page_Load(object sender, EventArgs e)
{
if (Session["datalist"] != null)
((DataList)Session["datalist"]).SelectedIndex = (int)Session["index"];
}
The probelm with your code is that the Page.IsPostBack property will be false in the initial get request and for every page reload (actual postback) it will be true. Thus !Page.IsPostBack will become actually false and your code will never execute.