ASP.NET StateBag and Custom Controls

Question

Lets pretend that for some reason I want to create a custom control that is derived from Control and not WebControl. Let us also assume that I need to process attributes (ie implement IAttributeAccessor) and that I want to do so by using an AttributeCollection just like WebControl does.

WebControl implements the Attributes property like this:

public AttributeCollection Attributes
{
    get
    {
        if (this.attrColl == null)
        {
            if (this.attrState == null)
            {
                this.attrState = new StateBag(true);
                if (base.IsTrackingViewState])
                {
                    this.attrState.TrackViewState();
                }
            }
            this.attrColl = new AttributeCollection(this.attrState);
        }
        return this.attrColl;
    }
}

Note the following:

1. You cannot create an AttributeCollection without giving it a StateBag.
2. We have to create a new StateBag. It is not wise to reuse the controls StateBag because an attribute may have the name as a value stored by the control.
3. We cannot call TrackViewState on the StateBag because this is an internal method.
4. StateBag is a sealed class.

So as I understand it if I want to use an AttributeCollection I have to use a new StateBag which can never (without resorting to tricks like reflection) actually manage state correctly.

Am I missing something?

Answer 1

To call TrackViewState on a custom StateBag, you have to cast it to its interface.

StateBag mybag = new StateBag();
(mybag as IStateManager).TrackViewState();

I'm guessing this design decision was made to hide the implementation of ViewState from consumers. There is some information about implementing custom state tracking on the documentation page for IStateManager .