I have a question about the code behind of the ArticleListing.ascx.cs user control. What is the purpose of the line of code

this.Page.RegisterRequiresControlState(this);

in the Page_Init()?

It wasn't explained in the book. Thanks

According to MSDN "Custom server controls that use control state must call the RegisterRequiresControlState method on each request because registration for control state is not carried over from request to request during a postback event. It is recommended that registration occur in the Init event." for more information about Control State take a look at Control state in ASP.NET 2.0

Sometimes, you need a way for a user control to remember its properties across postbacks, just like a regular control does.

Controls do this by storing and retrieving their values from the page's state bag. Regular controls use the ViewState. User controls use ControlState.

This line merely tells the containing page that the ArticleListing.ascx.cs intends to store its properties in the page's ControlState. The actual work of storing and retrieving the values is done in the SaveControlState() and LoadControlState(object SavedState).

So why in the Polls chapter only the PollID property of the PollBox user control is saved to the ControlSate. Why not save the other properties as well such as ShowArchiveLink and ShowHeader etc... ? Thanks

Annddrew:

So why in the Polls chapter only the PollID property of the PollBox user control is saved to the ControlSate. Why not save the other properties as well such as ShowArchiveLink and ShowHeader etc... ? Thanks

Because the PollID is the only property which actually needs to be stored by the PollBox user control. The other properties refer to "real" server controls inside the user control. The value of these server controls are already stored in Viewstate. For example, look at ShowArchiveLink

public bool ShowArchiveLink
        {
            get { return lnkArchive.Visible; }
            set { lnkArchive.Visible = value; }
        }

The value of the ShowArchiveLink property is gotten from the value of lnkArchive.Visible. The properties of lnkArchive are already stored in Viewstate.

PollID, on the other hand, is not connected to any of the server controls, and thus cannot be retrieved from Viewstate. 

Ok thank you very much Lee Dumond. Now I got it.