Question

I have an UpdatePanel and in my updatepanel_Load I have some code which looks like this:

if (!IsPostBack || triggeredRefresh.Value == "1") 
{
create hidden fields and add to list using
itemFields.Add(newField);
} 
else if ( triggeredCheck.Value == "1" )
{
lookup field values
}

The list is declared at class level using:
List itemFields = new List();

The problem is that whenever I want to lookup values in the hidden fields the list is empty. Why is it empty at this point and how can I fix it?

Thanks

Answer 1

Class level fields are not persisted between postbacks. Use the Session state Collection to persist values. For persisting controls, you can use <asp:PlaceHolder />.

EDIT:

If you are using the HiddenField to just store a single value and access from server side and if it’s not being accessed from client script, you can do something like this.

Remove your class level list.

if (!IsPostBack || triggeredRefresh.Value == "1") 
{
    Session["someValueKey"] = 0;
} 
else if ( triggeredCheck.Value == "1" )
{
    var x = Convert.ToInt32(Session["someValueKey"]);
}

if you do need a list of values, then you can do

if (!IsPostBack || triggeredRefresh.Value == "1") 
{
    Session["someValueKey"] = new List<int>{100,200};
} 
else if ( triggeredCheck.Value == "1" )
{
    var x = Session["someValueKey"] as List<int>();
}

if you do need it to be a control (to access from client script) you can do

if (!IsPostBack || triggeredRefresh.Value == "1") 
{
   HiddenField hiddenField = new HiddenField();
   hiddenField.ID ="hiddenField1";
   hiddenField.Value = "0";
   placeHolder1.Controls.Add(hiddenField);
} 
else if ( triggeredCheck.Value == "1" )
{
    HiddenField hiddenField = placeHolder1.FindControl("hiddenField1") as HiddenField;
    var x = Convert.ToInt32(hiddenField.Value);
}