Question

I’ve got a page with several controls, such as Checkboxlists and two containers holding search results.

I’ve been told to make this site persistent, so the user can come back from anywhere while browsing our site and find it’s settings restored (read: boxes stll checked; results still available)

So far I have tried to override SavePageStateToPersistenceMedium and LoadPageStateFromPersitenceMedium, but I am constantly running into a yellow screen of death as soon, as I click a button on the page.

protected override void SavePageStateToPersistenceMedium(object viewState)
{
    string str = "VIEWSTATE_" + Request.UserHostAddress;
    Cache.Add(str, viewState, null, DateTime.Now.AddMinutes(Session.Timeout), TimeSpan.Zero, CacheItemPriority.Default, null);
    ClientScript.RegisterHiddenField("__VIEWSTATE_KEY", str);
    ClientScript.RegisterHiddenField("__VIEWSTATE", "");
}
protected override object LoadPageStateFromPersistenceMedium()
{
    string str = Request.Form["__VIEWSTATE_KEY"];
    if (!str.StartsWith("VIEWSTATE_"))
    {
        throw new Exception("Invalid viewstate key:" + str);
    }
    return Cache[str];
}

Is there anything wrong with my code and what would I need to call to retrieve the Viewstate on Page_Load or Page_init to retrieve it?

edit:
Here is the approach to solve it via session[“xyz”]

List<ListItem> selectItems = new List<ListItem>();
        foreach (ListItem item in CheckBoxListLevel.Items)
        {
            if (item.Selected)
                selectItems.Add(item);
        }

        Session.Add("SavedLevelItems", selectItems);

//And then in Page_Load

   if (Session["SavedLevelItems"] != null)
    {
        List<ListItem> SessionList = (List<ListItem>)Session["SavedLevelItems"];
        foreach (var item in SessionList)
        {
            if (item.Selected)
            {
                CheckBoxListLevel.Items.FindByText(item.Text).Selected = item.Selected;
            }
        }
    }

However, if I view a searchresult and then just fire a GET to get back to the initial page, all stored items are not rendered correctly.

Answer 1

The solution was pretty simple in the end.
I only needed the state of some controls and not the whole page, since the results could change anytime.

The problem was, that the datasources for the CheckBoxLists was defined in the aspx file.
this resulted in no items being loaded when I tried to access the controls via Page_Load().

So i transferred the whole data access logic to the code behind file, wrapped in an if statement. If a fitting session object is available the datasource is the session object, else take it from the database.

 protected void fillEntrylevelList()
{
    using (OleDbConnection connection = new OleDbConnection(ConfigurationManager.ConnectionStrings["TestEnvironment"].ConnectionString))
    {
        string EntrylevelQuery = @"INSERT SQL STATEMENT HERE";
        OleDbCommand command = new OleDbCommand(EntrylevelQuery, connection);
        if (Session["SavedLevelItems"] != null)
            {
                CheckBoxListLevel.Items.Clear();
                List<ListItem> SessionList = (List<ListItem>)Session["SavedLevelItems"];
                foreach (var item in SessionList)
                {
                    try
                    {
                        CheckBoxListLevel.Items.Add(item);
                    }
                    catch { }

                }
            }
        else
        {
            connection.Open();
            CheckBoxListLevel.DataTextField = "bez_level";
            CheckBoxListLevel.DataValueField = "id_level";
            OleDbDataReader ListReader = command.ExecuteReader();
            CheckBoxListLevel.DataSource = ListReader;
            CheckBoxListLevel.DataBind();
            ListReader.Close(); ListReader.Dispose();
            GC.Collect();
        }
    }
}

kind regards