Planet wrox sample website: Loss of ViewState

sirish_kumar · March 27th, 2012, 04:00 AM

Hi to all,
This refers to the sample website "Planet Wrox" downloaded from p2p. I added a page "PictureDetails.aspx" in the "PhotoAlbums" folder so that it shows an enlarged image of the thumbnail that is clicked in the "Gigpics" page. After seeing the full image when I navigate back (either by pressing back button of browser or by clicking Gigpics link the dropdown goes back to the the first item in choice and the thumbnails disappear.

I checked the viewstate propery of the dropdown list, the image listview and also added "enableviewstate = "True" in the page directive.

Still I cannot understand why it the drop down goes back to the first element and the thumbnails vanish.

Any help in solving this will be highly appreciated.

One more feature I am thinking of adding is to display the date of uploading below all the thumbnails in the gigpics page. The system date should be automatically added whenever a user uploads an image. I added a column "DtUpLded" in the "Picture" table but how to populate it with current date?

Regards

Sirish.

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Pages & codes added:
source of PictureDetails.aspx
-----------------------------------------

Code:

<%@ Page Language="VB" MasterPageFile="~/MasterPages/MasterPage.master" AutoEventWireup="false" CodeFile="PictureDetails.aspx.vb" Inherits="_Default" Title="Full Size Image" %>

<asp:Content ID="Content2" ContentPlaceHolderID="cpMainContent" Runat="Server">
    <asp:Image ID="image1" runat="server" ImageAlign="Middle" Width="600" />
</asp:Content>

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code of PictureDetails.aspx.vb
-----------------------------------------------------

Code:

Partial Class _Default
    Inherits BasePage

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

    End Sub
    Protected Sub Image1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Image1.Load
        Dim imgUrl As String = Request.QueryString.Get("ImageUrl")
        image1.ImageUrl = imgUrl
    End Sub
End Class

------------------------------------------------------------------

Added the following code under ItemTemplate of the Listview to create the Hyperlink for each thumbnail

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Code:

<asp:HyperLink ID = "HyperLink1" runat="server" NavigateUrl= '<%# "PictureDetails.aspx?ImageUrl="+Eval("ImageUrl") %>' >
						<asp:Image ID="Image1" runat="server" ImageUrl='<%# Eval("ImageUrl") %>' ToolTip='<%# Eval("ToolTip")%>' />
						</asp:HyperLink>

------------------------------------------------------------------

Imar · March 27th, 2012, 04:21 AM

Hi there,

This is not related to ViewState or control state, but to AJAX. The pictures are loaded through an AJAX call because the entire list control is wrapped in an UpdatePanel. The browser doesn't keep track of these changes so when you click Back, it loads the page it initially loaded and doesn't reapply the AJAX call. A few ways to fix this:

1. Modify the list page so it responds to IDs in the Query String as well. That way, when an ID is found in the query string you can preselect the right item in the drop down list. Then in the details page, supply a "back" link that submits the photo album ID.

2. Drop the UpdatePanel.

3. Implement AJAX history: https://www.google.com/#q=implement+history+UpdatePanel

Cheers,

Imar