Anatomy of an ASP.NET Page

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Anatomy of an ASP.NET Page
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Compiling an ASP.NET Page

• An ASP.NET page is compiled when it is rendered
  for the first time
• A page is compiled to a class that derives from
  Page
• Parse the .aspx file and create a class that
  derives from Page
• The preceding class is then compiled to an
  assembly
• This process is transparent

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Compiling an ASP page(Illustration)
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IIS File Mappings

• .asax application files
• .ascx ASP user controls
• .asmx Web services
• .aspx ASP.NET Web pages

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Processing Directives

• Processing directives are used to configure the
  runtime environment
• Directives can appear anywhere on a page but best
  practices dictate that they appear at the
  beginning of the page
• Directives begin with lt_at_ and end with gt
• Make sure you dont forget the gt

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Processing Directives

• Processing directive are used to configure the
  runtime environment
• Processing directives have the following format
• lt_at_ directive_name attributevalue
  attributevalue gt

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Processing Directives (_at_ Page)

• It can appear only in .aspx pages
• Attributes are divided into roughly three
  categories
• Compilation
• Page behavior
• Page output
• There are other tools to configure the same
  options beyond processing directives

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Processing DirectivesPage Compilation

• See Table 3-5 on page 104 for a complete list
• CodeFile lists the file containing the VB or C
  code for the .aspx page
• Language describes the programming language for
  the CodeFile
• ClassName explicitly sets the name of the class
  created upon compilation

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Processing Directives(Referenced Assemblies)

• Most assemblies are automatically provided by the
  compiler
• Assembly references can also be added using the
  _at_Assembly directive
• Assembly references can also be added in the
  web.config file

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Introduction to the Page Class

• The Page class provides the basic behavior for an
  ASP Web page
• Its objects allow you to reference
• The application itself (Application)
• The server itself (Server)
• The HTTP request (HttpRequest)
• The HTTP response (HttpResponse)
• The users session (Session)

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Page Class Properties (1)

• Controls returns a collection of controls on the
  page
• IsPostBack indicates whether the page is being
  loaded in response to a postback or is being
  loaded for the first time
• PreviousPage returns a reference to the caller
  page
• Only meaningful in case of a cross-page postback
• Check IsCrossPagePostback

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Page Class Properties (2)

• ClientTarget allows you to specify the type of
  browser
• Note that automatic browser detection is disabled
• EnableTheming and Theme allows you to set page
  themes (more later)
• MaintainScrollPositionOnPostback allows the page
  position to be persisted from one postback to the
  next

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Page Class Methods (1)

• DataBind binds all data bound controls to their
  data sources (more later)
• Validate causes validation controls to validate
  their data
• SetFocus sets input focus to the desired control
  instance
• There are methods to work with client script

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Introduction to Page Events

• First, this topic is very important to getting
  your ASP applications to work
• ASP uses the eventing model to
• Persist state from one postback to the next
• Create static and dynamic controls
• Bind control instances to data sources
• And much more
• As your book says state is an illusion of
  continuity

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Page Life Cycle (1)

• When a page is requested
• The runtime figures out why the page is being
  processed
• Normal request
• Postback
• Cross-page postback
• callback

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Page Life Cycle (2)

• PreInit Event
• Its the first event in the page life cycle
• Master page has not been associated
• Themes have not been associated
• Its possible to change master page or theme
  association at this time
• IsCallback, IsCrossPagePostback and IsPostBack
  are set at this time
• Control instances have been created

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Page Life Cycle (3)

• Init Event
• Master page and theme have been set and cannot be
  changed
• Child controls are initialized and the ID is set
• Child controls are initialized recursively
• Init event fires for all child controls before
  the event fires for the page itself

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Page Life Cycle (4)

• InitComplete event
• Here, viewstate tracking is turn on
• The event fires only for the page
• PreLoad event
• System initialization is complete
• We dont typically do much here

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Page Life Cycle (5)

• Load event
• The event is raised first for the page and then
  recursively for all child controls
• You can access control properties and view state
  at this time
• Create dynamic controls in this event
• Use IsPostBack to check whether the page is being
  loaded in response to a postback or new page

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Page Life Cycle (6)

• LoadComplete fires after Load
• At this point, the page begins its rendering phase

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Page Life Cycle (7)

• PreRender event
• Fires for the page first and then recursively for
  all controls
• Use to update controls before the output is
  rendered
• PreRenderComplete event
• Raised only for the page after PreRender has
  fired for all child control instances

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Page Life Cycle (8)

• SaveStateComplete event
• It fires for all constituent controls and then
  the page itself Next, the markup is generated
• Unload event
• After rendering, the event fires for all control
  instances and then the page itself
• Use this event to close files or database
  connections