Programming Visual Basic 2005

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 recreated from scratch. Unless you explicitly preserve the state of all the controls 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. This section will explore how that is done and how you can use the ASP.NET state management capabilities.

ASP.NET manages three types of state :

• View state (which is saved in the state bag)

• Application state

• Session state

Table 8-2 compares the different kinds of state.

Table 8-2. State types

Variables	View state	Application state	Session state
Uses server resources	No	Yes	Yes
Uses bandwidth	Yes	No	Depends
Times out	No	No	Yes
Security exposure	Yes	No	Depends
Optimized for nonprimitive types	No	Yes	Yes
Available for arbitrary data	Yes	Yes	Yes
Programmatically accessible	Yes	Yes	Yes
Scope	Page	Application	Session
Survives restart	Yes	No	Depends

The following sections will examine each type of state.

View State

The view state is the state of the page and all its controls. The view state is automatically maintained across posts by the ASP.NET Framework. When a page is posted to the server, ...