ViewState in ASP.NET 2.0

There is one other important place where view state is used, and that is in controls that issue server-side change events. If the user changes the value in a textbox or switches the selected element in a dropdown list, you can register an event handler and have code execute when the event is raised. If you disable view state on a control whose change notification event you are handling, it won't fire correctly since it must always assume that the previous value was the same as the default value in the form.

View state issues

There are many issues with view state in ASP.NET 1.x. It is on by default, and unless you know to look for it and disable it when it is not needed, it can significantly increase the amount of data rendered by your page. This becomes particularly painful when you use data-bound controls, all of which use view state to save their state across postbacks.

If you want to use features like sorting, paging, or editing in the DataGrid, you cannot disable its view state.

View state must encode not only the data but also the type of data (metadata); also, base64 encoding generally adds about 33 percent space overhead.

The primary rule to follow when optimizing view state usage on your site: if you populate the contents of a control every time a page is requested, it is generally safe (and wise) to disable view state for that control.

On the other hand, you may decide to take advantage of the fact that view state is going to retain the state of your controls and only populate control contents on the initial GET requests to a page (just falling through on subsequent POST requests).

View State Improvements in ASP.NET 2.0

• The serialization format for view state will be changed. This will dramatically decrease the size of view state.
• Microsoft will partition the view state into two separate and distinct categories: view state and control state. Control state is another type of hidden state reserved exclusively for controls to maintain their core behavioral functionality, whereas view state only contains state to maintain the control's contents (UI). Control state is stored in the same hidden field as view state (being just another leaf node at the end of the view state hierarchy).

You can find all the contents of this post from Fritz Onion's article: Speed Up Your Site with the Improved View State in ASP.NET 2.0. Read it in more detail.