CIS 451: ASP.NET Objects

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CIS 451 ASP.NET Objects

• Dr. Ralph D. Westfall
• January, 2009

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Object Oriented Programming

• many popular newer programming languages are
  object-oriented
• C, Java, JavaScript
• Visual Basic.NET is a true object-oriented (OO)
  language
• in contrast to VB 6 (which however did have
  objects with very useful properties)

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What Is an Object?

• 3 types of things grouped together
• properties (like variables descriptive)
• like a "super" variable (cf. hours PM)
• methods (like functions actions)
• events (things that it responds to)
• similarities with real world objects
• car (properties? methods? events?)
• dog " "

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Object Features

• properties name/value pairs
• age 21 height 66" weight 135
• methods code that does something
• calculations, write to screen, send e-mail
• may have either/both of following
• parameters (inputs)
• return values (outputs)

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Object Features - 2

• events things happen, object responds to them
• like a method, but triggered externally
• user clicks a button, or time runs out
• can have parameters and/or return values
• asynchronous can occur at any time
• rather than scheduled, or at same time as
  something else (synchronous)

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Other Object Concepts

• class template or general model
• instance of class has specific attributes
• telephone class, my phone instance
• encapsulation details of object hidden
• inside a "black box"
• only need to know the interface how to call the
  methods and what the inputs and/or outputs are

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Other Object Concepts - 2

• "dot" notation identifies attributes and methods
  of objects
• Request.TotalBytes
• Request.QueryString.Count
• Count (of arguments) in QueryString is a property
  of Request Object
• Response.Write()
• Write is a method of Response Object

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ASP Core Objects

• Request messages from caller (e.g., web page or
  process)
• Response messages to caller (browser)
• Server variables and utility functions
• Application data storage in memory for all web
  pages in the application
• Session identifies individual user interactions

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Request Object

• html or another asp file requests an asp file
• Request Object has information from page that
  requested the asp file
• information is stored in "collections"
• contain pairs of variable names and their values
  (name/value pairs)
• data values can be accessed by item name
• Request.QueryString("page")

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Request Object Data

• "get" method in HTML calling page
• ltform action"buya.aspx" methodgetgt
• "get" appends data to URL (URL encoding)
• limit around 1000 characters (256 2000)
• data available in Request.QueryString
  "collection," indexed by name of form element
• Request.QueryString("page")
• form has textbox, textarea, checkbox, radio
  button, or etc. element with name"page"

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URL Encoding

• ? after URL shows start of data
• pairs of namevalue
• (ampersands) between pairs
• between separate words ( space)
• special characters coded as nn ( is 2B)
• http//www.company.com/search.asp?
• ?custJabbaraddress23110thSt
• example try doing a Yahoo search

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Request Object Data - 2

• "post" method in HTML calling page
• ltform action"buya.aspx" methodpostgt
• sends data by a separate route
• size is essentially unlimited
• data available through Request.Form "collection,"
  indexed by name of form element
• Request.Form("prod1")
• form has textbox, textarea, checkbox, radio
  button, or etc. element with name"prod1"

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Get versus Post

• get (Request.QueryString) object.property)
• better for debugging (can look at query string in
  URL box on browser)
• post (uses Request.Form)
• can handle more data
• safer (less susceptible to hacking)
• always use post for database updates
• easy to convert Request.QueryString to
  Request.Form with global search/replace

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Using QueryString in an aspx File

• can create the same effect sending from an aspx
  file as from a html file
• Response.Redirect("rsp.aspx?Name" _
• this.txtName.Text "LastName" _
• this.txtLastName.Text)
• values are URL encoded and visible in browser
  address of destination page
• one way to migrate from html to aspx

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Response Object

• sends information to client
• can control when and how to send it
• can control caching/expiration of page
• can send parts or all of a web page to client

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Response Methods

• Response.Write(x1 " " x2 ...)
• x1 etc. can be anything printable (text, s,
  etc., or functions that return printable
  characters)
• .NET has parentheses hold argument(s)
• lt x1 " " x2 " " etc.gt
• same effect as Response.Write, in less space
• less efficient (don't use lt a lot)

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Response Methods - 2

• redirecting to another page
• Response.Redirect("buya.aspx")
• stops processing on current page and goes to the
  other page
• can go to external pages too

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Server Transfer Method

• can also use to redirect to another page, but
  only if it's on same server
• Server.Transfer("buya.aspx")
• doesn't change URL in browser address
• comparison of Response.Redirect and
  Server.Transfer

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Exercise Form Processing

• use Dreamweaver to create a form that uses 8
  form elements/variations in its
  WindowsgtObjectsgtForms toolbar
• set name property for each element
• select options (e.g., text input can be single or
  multiline, or password)
• see HTML Form Reference for syntax
• save file as a .html file

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Exercise Form Processing - 2

• use Visual Studio to
• create a project
• add the .html file you created on the previous
  page to the project
• create a .aspx file with Response.Write
  statements to print inputs/selections from each
  input element from the .html file
• test it on your workstation or computer

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Multiple Selection Data

• can allow multiple selections in a list box on a
  form
• ltselect size2 name"loc" multiplegt
• ltoptiongtParislt/option gt
• ltoptiongtSydneylt/option gt
• ltoptiongtBuenos Aireslt/option gt
• lt/selectgt
• may send multiple items with same name ("loc" in
  this example)

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Multiple Selection Data - 2

• For intI 1 to _
• Request.Form("loc").Count
• Response.Write _
• (Request.Form("loc")(intI))
• Next
• note dot connecting Form object's ("loc") item to
  Count