Thursday, April 26, 2007

Saving Page ViewState out of the page!

If you look for solutions to get rid of huge ViewStates from your pages you will get a lot of people telling you to override SavePageStateToPersistenceMedium and LoadPageStateFromPersistenceMedium in your pages and do complicated stuff like keeping the ViewState in the Cache or in a database, calculating strange keys, etc.

No more! Net 2.0 has something called a PageStatePersister. It is an abstract class and every Page has one. In case no override occurs, the default is a HiddenFieldPageStatePersister, but you can also use the provided SessionPageStatePersister like this:
protected override PageStatePersister PageStatePersister
return new SessionPageStatePersister(this);

And that's it! It works with Ajax and UpdatePanel, too.

However, this is no "Silver Bullet", as the SessionPageStatePersister will have issues with multiple windows open with the same session (like pop up windows) as exampled in this nice article. Also check out this situation when, during Ajax callbacks, a full ViewState is returned due to the ever troublesome ImageButtons.

There is no reason not to create your own PageStatePersister, though. The abstract class is public (not internal and sealed as Microsoft likes their most useful classes) and you can inherit it. You can even store the state in the Cache! :)

A very comprehensive article on ViewState is here.