Understanding ASP.NET Page Life Cycle and Directives, Slides of Computer Programming

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Anatomy of an ASP.NET

Page

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

IIS File Mappings

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

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 <%@ and end with %>  Make sure you don’t forget the %>

Processing Directives

( @ 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

Processing Directives

Page 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

Introduction to the Page Class

 The Page class provides the basic behavior for an ASP Web page  It’s objects allow you to reference  The application itself ( Application )  The server itself ( Server )  The HTTP request ( HttpRequest )  The HTTP response ( HttpResponse )  The user’s session ( Session )

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

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

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”

Page Life Cycle (2)

 PreInit Event  It’s the first event in the page life cycle  Master page has not been associated  Themes have not been associated  It’s 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

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

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

Page Life Cycle (6)

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