Question

I am dynamically loading user controls to switch between views in my project. I am aware that I need to reload my user control on every postback. The odd thing is my viewstate for the control is maintained even though the control is gone? I confirm that the panel I loaded it into is empty and then I check the view state and my value is there.

What’s stranger is that if I load a different control, it can see the viewstate from the previous control? I checked and my page cannot see viewstate from my dynamically loaded control and visa versa. This makes me think the user control is treated as its own page. The confusing part is why the second view I load can see values from the first and why the values are there even though I the control has disappeared?

I also find this section of the code to be useless. Why is it removing the control? The panel is always empty (the code is from Telerik):

string controlId = LatestLoadedControlName.Split('.')[0];
Control previousControl = pnlControlPlaceholder.FindControl(controlId);
if (!Object.Equals(previousControl, null))
{
   this.pnlControlPlaceholder.Controls.Remove(previousControl);
}

I looked at several posts and most say that viewstate is lost on every postback, although this is not the case for me. Perhaps because I’m using update panels. Although if an intial request handles an event and then reloads the same control again, the viewstate is lost. It only seems to preserve the viewstate on the very next postback.

Can anyone explain this odd behavior of sharing viewstate between user controls or why it is there even though the control is lost?

Answer 1

Apparently you can read viewstate between pages in two scenarios… Cross page postback and when using Server.Transfer. I believe the cross page postback scenario would explain what I am seeing.