CODEWITHSUNDEEP
c#asp.netviewstate
AaronLS
AaronLS

Reputation: 38384

How to ignore viewstate of a previous request for particular control?

I am dynamically generating controls, and sometimes I want to create a control and have it ignore the viewstate. For example, sometimes the user has clicked a button indicating they want a different form loaded, so the control tree I generate on postback is different from the original control tree. This is fine, except when I call Controls.Add then it tries to load the viewstate form the old controls into the new controls if the control tree structure is similar, and I want them to instead ignore that viewstate(and also ignore the postback values for input controls as well).

Can I do something like set the IDs of the controls or something that would allow me to conditionally prevent them from getting the viewstate/postback data of the previous request?

Edit: If I let the user of the control load the form on demand in postback handler, the postback data is not applied when I call Controls.Add(this really seems like a flaw in ASP.NET, because I would think if you're going to apply viewstate data "after the fact" through Controls.Add, it'd seem you would then apply the postback data automatically as well after the viewstate data is loaded). The real problem I run up against is my control is very dynamic, but the user of my control can't really tell it what to do until their postback handler fires, because one of the things a user can do is select different forms to be loaded via some link buttons. So it's not until the postback handler runs that they know what the uesr requested, and thus can ask my control to load a certain form. So I have to ask them to do convaluted things like saved the formID that identifies the last form to a session variable, and in OnInit they tell my form what the old formID was via a property. My control then loads the form in OnLoad so that it can consume the viewstate and postback data, and later in the programmer's postback handler, they can choose to clear the form and load a different one if they want.

Edit2: FYI Generating IDs for each control unique to the form works great, so I thought I could eliminate the pointless loading of the old form until the programmer requests a form be loaded in his postback handler. But as I mentioned above, what I found was that loading the form after postback data handling has occurred means that data is lost. Whereas viewstate gets loaded via Contorls.Add, playing catch up in the page lifecycle, it seems postback data does not! So it seems I am defeated at every turn.

Upvotes: 1

Views: 1990

Answers (4)

Mrinal Saurabh
Mrinal Saurabh

Reputation: 978

You must be generating dynamic controls on postback in pageload:

    protected void Page_Load(object sender, EventArgs e)
    {
      --Generate Dynamic Controls--
    }

You need to do it like:

    protected override void OnInitComplete(EventArgs e)
    {
        base.OnInitComplete(e);
    }

    protected void OnInit()
    {
     --Generate Dynamic Controls--
    }

    protected void Page_Load(object sender, EventArgs e)
    {

    }

Upvotes: 1

InfinitiesLoop
InfinitiesLoop

Reputation: 14629

You're going to avoid problems if you play along with the control lifetime. Basically, whenever you have a control that renders, it's best to ensure that control is recreated on the next postback, even if you aren't going to need it anymore. The first goal of a postback should be to restore the previous state -- only THEN do you make changes to it.

I described it best in this answer:

Wrong state in Server Controls with same ID's when dynamically adding UserControl to UpdatePanel

Upvotes: 3

ChrisLively
ChrisLively

Reputation: 88072

Have you tried just calling controls.clear prior to adding in the new ones?

UPDATE

I'm starting to believe that you are generating the controls at the wrong point in the page lifecycle. What is your flow?

Upvotes: 1

womp
womp

Reputation: 116987

Giving the controls different ID's would certainly prevent ViewState from being loaded, that would be one way.

You may also be able to manipulate the ViewStateMode property of your controls by setting it to "Disabled". I'm not sure if this prevents it from loading (it definitely prevents them from saving viewstate), but you could try it.

Upvotes: 2

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