Programming ASP.NET 3.5, 4th Edition

State

State is the current value of all the controls and variables for the current user in the current session. The Web is inherently a stateless environment, which means that every time a page is posted to the server and then sent back to the browser, the page is re-created from scratch. Unless the state of all the controls is explicitly preserved before the page is posted, the state is lost and all the controls are created with default values. One of the great strengths of ASP.NET is that it automatically maintains state for server controls—both HTML and ASP.NET—so you do not need to write any code to accomplish this. This section will explore how this is done and how you can make use of the ASP.NET state management capabilities.

ASP.NET manages four types of state:

• View state (which is saved in the state bag, covered later in this chapter)

• Control state

• Application state

• Session state

Control state (described shortly in conjunction with view state) cannot be modified, accessed directly, or disabled. Table 6-5 compares the other kinds of state management.

Table 6-5. Comparison of types of state

Feature	View state	Session state	Application state
Uses server resources	No	Yes	Yes
Uses bandwidth	Yes	No	No
Times out	No	Yes	No
Security exposure	Yes	Depends on configuration	No
Optimized for nonprimitive types	No	Yes	Yes
Available for arbitrary data	Yes (if data is serializable)	Yes	Yes
Programmatically accessible	Yes	Yes	Yes
Scope	Page	Session	Application
Survives application restart	Yes	Depends on configuration	No

The following sections ...