typical web page, it is very common for data entry forms to retain
their values after the form has been posted and the same page is
returned to the client (that is, to retain the values from a posted
form in the postback). To implement this feature in classic ASP, you
need to determine whether or not the page is requested by a client
for the first time. You also need to write code that will display the
submitted value in the controls. In contrast, ASP.NET performs state
management automatically in postbacks.
ASP.NET uses a simple hidden HTML form field to retain the values
automatically during postbacks. There are no ActiveX controls or
applets or client-side scripts used to maintain state. Thus, you need
not write code to retain values explicitly.
ASP.NET maintains only the state of server controlsi.e., the
controls declared with the runat="server"
attribute/value pair. State management can be enabled or disabled for
individual controls or an entire page by setting the MaintainState
property to True (its default value) or
Now let's revisit
the concept of ViewState, which was introduced earlier in this
chapter. ViewState is a collection of information about the
properties of an ASP.NET page and its controls (maintained in a
hidden form field named _VIEWSTATE). Since
control state on the server does not exist once the page has been
rendered to the client, ViewState exists to store the value of
properties of controls on the page. As the name itself implies,
ViewState preserves the state associated with a particular view of a
page. It is used by the noninput controls (such as Label and
DataGrid) to store their ambient state across requests. Thus, when a
page is posted back to the server, and the result of the postback is
rendered to the browser, controls such as textboxes and listboxes
will automatically retain their state, unless the
control's EnableViewState property has been set to
False or the state of the control was modified
programmatically on the server.
Only base properties are persisted in the ViewState. Any change in
these properties before rendering the page will be persisted.
If your page is not posted back to itself, you can set the
property EnableViewState to False at the page
level (via the @ Page directive) to avoid the
extra processing and storage space required for maintaining
ViewState. You can also disable/enable view state on a per control