ASP'NET Introduction, Creating a Site, Debugging

1
ASP.NET Introduction, Creating a Site, Debugging

• David Turton
• Conestoga College
• Institute of Technology Advanced Learning
• http//www.conestogac.on.ca/dturton
• Doon 1D17 x3610

2
Objectives

• Static vs dynamic web pages
• HTML controls
• HTML Server controls vs. ASP.NET controls
• ASP server-side processing
• Request/Response
• QueryString, ServerVariables, Redirection
• Page events
• Event-driven programming
• Creating a site web pages in VS.NET 2008
• Hello World! yes, there are tricks
• Debugging Code

3
Static and Dynamic Web Applications

• HTML is used to create static content
• Dynamic Web pages are created in response to user
  input
• Shopping carts
• Patient/customer/membership records
• Online orders with inventory checks
• Keyword search into records
• Personalized web sites
• Appointment books

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Server-side Programming

• Create dynamic Web pages
• Populate controls from a database
• Create/modify HTML content on the fly
• Processing occurs on the server
• Hides process code from users nasties
• Sends static HTML to the browser
• Site becomes browser-independent
• Active Server Pages (ASP)
• Microsoft's implementation of dynamic web pages
• ASP.NET
• .NET framework provides control elements
• Speeds web page development
• Example build a lttablegt vs populate a .NET grid

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Processing Web Pages with ASP

• Client requests a page
• ASP engine retrieves
• HTML template
• Code behind the page
• Does global processing
• Adds user controls (server-side includes)
• Executes the code behind the page
• Modifies page contents
• Renders an HTML page as a response to the browser

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ASP.NET Web FormTwo logical parts

• HTML template
• User interface or presentation layer
• Content
• Controls (HTML elements)
• How page is formatted
• Controls
• HTML elements
• HTML Server controls
• ASP.NET controls
• Filename extension .aspx

• Code Behind the Page
• Server program
• Separate file
• Queries modifies controls on page
• ASP.NET compatible language
• Visual Basic .NET, C, Perl, Java, COBOL, etc.
• Filename same as Web Forms
• file extension identifies the language
• .vb - Visual Basic .NET
• .cs C

Not recommended
HelloWorld.aspx ? HelloWorld.aspx.vb
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HTML Server Controlscan be made accessible by
your code

• HTML Server controls
• Add attributes runat "server" and id "someId"
• HTML control
• ltinput type"text"gt
• HTML Server controls
• ltinput type"text" runat"server" id"userName"/gt
  
• ltinput typeradio runatserver valueYes
  id"visa"/gt Visa
• Server-side programs can interact with server
  controls
• Identified by the id property
• Rendered into a plain HTML control
• Sent to the browser
• Controls can be eliminated from the form sent to
  the browser
• userName.Visible False

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ASP.NET Controls

• Microsofts version of most HTML controls
• Are rendered into HTML code
• So any browser can handle the results
• Are organized as
• Form Controls
• Data Validation Controls
• User Controls
• Data Controls
• Identified by the prefix asp
• Followed by the name of the control

ltaspButton id"btnShow" runat"server"
Text"Show message." /gt
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HTML Server Controls vsASP.NET Server Controls

• Different properties
• HTML Server controls values vary by type
• lblProductName.InnerHTML "Product"
• txtFirstName.Value"David"
• ASP server label control value usually .Text
• lblProductName.Text "Product"
• txtFirstName.Text "David"
• Hint let intellisence in VS.NET help you
• Start typing will show you similar control
  names
• VB type "me." first
• Place period after control name
• Will display properties methods available
• Pick most likely property or method
• Will describe parameters, if any

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PostbackOnce the HTML is rendered, the program
code is dropped,all variables are flushed,
database result tables are lost

• "Maintaining State"
• Retaining information between web requests
• Retain data on form, including data from
  invisible controls
• Does not retain program variables
• "Postback"
• sending user data to the server.
• __ViewState
• Hidden encrypted field on page ltinput
  typehidden /gt
• Servers scratch pad
• Browser holds scratch pad, not server
• Example web site with 10 requests a second
• 90 are not serious queries
• Why would you hold info about each request?
• How long do you hold it?
• Would you want to manually code the data
  retention routines?

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Postback Data__ViewState Hidden Field

• lt!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0
  Transitional//EN" "http//www.w3.org/TR/xhtml1/DTD
  /xhtml1-transitional.dtd"gt
• lthtml xmlns"http//www.w3.org/1999/xhtml"gt
• ltheadgtlttitlegt
• Untitled Page
• lt/titlegtlt/headgt
• ltbodygt
• ltform name"form1" method"post"
  action"logonForm.aspx" id"form1"gt
• ltdivgt
• ltinput type"hidden" name"__VIEWSTATE"
  id"__VIEWSTATE" value"/wEPDwUJNzgzNDMwNTMzZGSR4n
  g5EwWlrtoppSaTbbuyqunw" /gt
• lt/divgt
• ltdivgt
• ltspan id"lblName" style"width70pxtext-
  alignright"gtNamelt/spangt
• ltinput name"txtName" type"text"
  id"txtName" /gt
• ltbr /gt
• ltspan id"lblPassword" style"width70pxt
  ext-align right"gtPasswordlt/spangt
• ltinput name"txtPassword" type"text"
  id"txtPassword" /gt
• ltbr /gt
• ltinput type"submit" name"btnLogon"
  value"Logon" id"btnLogon" /gt

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Page Class Events

• Page Class
• variety of methods, functions, and properties
• can be accessed within the code behind the page
• When a page is requested by a client
• page events occur
• Page_Init event
• Initializes the page control hierarchy
• Only run once, when the page is first requested
• Page_Load event
• loads server controls into memory
• occurs every time the page is executed

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Page Class Event Cycle
Sub Page_Load(s As Object, e As EventArgs)
lblMessage.Text "Welcome!" End Sub
You work with these
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Event-Driver Programming

• Programs do nothing except in response to an
  event
• Page is loaded
• User clicks a button
• User changes a text box or drop-down selection
• This fires the appropriate Event Handler
• Control is passed back to server
• Instructions executed sequentially in the event
  handler
• No event handler
• Event ignored
• Control not passed to server
• Page_Load event doesn't fire

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Events for Controls on Page

• The user clicks the button
• ltaspButton ID"btnLogon" runat"server"
  Text"Logon" /gt
• The "click" event for the button fires
• And calls the event handler for it
• Private Sub btnLogon_Click(sender as object, e
  as EventArgs)
• btnLogon.Text "you clicked me!"
• End Sub

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Sample Event Handlers

• event page is loaded
• Private Sub Page_Load(sender as object, e as
  EventArgs)
• lblMessage.Text "Go ahead ... you know you
  want to."
• End Sub
• event user clicks button
• Private Sub btnClick_Click(sender as object, e as
  EventArgs)
• if (lblMessage.Text.Substring(0, 2) "Go")
  Then
• lblMessage.Text "Hello World!"
• else
• lblMessage.Text "Only once, please.
• EndIf
• End Sub

id of a label on the form
(yes, there's a logic fault in this code)
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Built-in ASP.NET Objects Objects built into the
Web Server

• HTTPRequest
• Information about the browser, fields on the
  form, cookies, digital certificates, etc.
• Sent with each page request
• HTTPResponse
• To send information to the browser
• To redirect it to another page
• Session
• To hold data for the duration of the connection
• Similar to cookies

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Page.Request Information

• properties
• Request.TotalBytes
• total bytes in the request
• Request.PhysicalPath
• Request.UserHostAddress
• Request.UrlReferrer.Host
• Request.Browser
• Request.Version
• Request.Platform
• methods
• Request.BinaryRead
• retrieve data sent as part of a POST request

• collections
• Request.ClientCertificate
• fields on the client digital certificate
• Request.Cookies
• cookies the client received from this server
• Request.QueryString
• variables in the query string following the page
  URL
• Request.ServerVariables
• environment variables.

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Request.QueryStringretrieving data from the URL
Query String

• retrieves variables in the URL query string
• Values following "?
• Use procedures to parse the string
• http//www.dave.com/reg.asp?firstNameDavehearra
  dheartv
• Request.QueryString full string after "?"
  in URL
• Request.QueryString.Count variables in
  query string
• Request.QueryString.Get("firstName") value of
  field by this name
• returns a comma-delimited string if field has
  several values (like "hear")
• Request.QueryString.GetValues(hear).GetValue(0)
• If field hear has several values, this returns
  the 1st one (index 0)

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Request.ServerVariablesenvironment request
header information

• HEADER_headername value stored in the header
  headername
• HTTP_headername same, but "_" in headername
  searched as "-"
• HTTPS returns ON if channel secured by SSL, OFF
  if not
• LOCAL_ADDR IP address of server receiving the
  request
• LOGON_USER account user is impersonating on web
  server
• REMOTE_ADDR IP address of remote client
• REMOTE_PORT client TCP response-port
• REQUEST_METHOD method used to send request GET,
  POST, PUT
• SERVER_NAME name of the server handling the
  request
• SERVER_PORT port number request was sent to on
  the server
• SERVER_PORT_SECURE 1 if request handled by secure
  server port
• URL base portion of the URL
• etc...

Request.ServerVariables.Get(LOGON_USER)
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Page.Request Accessing information about the
request the requester
Private Sub Page_Load(sender as object, e as
EventArgs) Response.Write("ltbgtPhys Path
lt/bgt" Request.PhysicalPath "ltbr/gt")
Response.Write("ltbgtUser Addr lt/bgt"
Request.UserHostAddress "ltbr/gt") If
Request.UrlReferrer IsNot Nothing Then
Response.Write("ltbgtReferrer URL lt/bgt"
Request.UrlReferrer.Host "ltbr/gt") End If
Response.Write("ltbgtBrowser lt/bgt"
Request.Browser.Browser "ltbr/gt")
Response.Write("ltbgtBrowser vers lt/bgt"
Request.Browser.Version "ltbr/gt")
Response.Write("ltbgtUser O/S lt/bgt"
Request.Browser.Platform "ltbr/gt")
Response.Write("ltbgtServer Variable AUTH_USER
lt/bgt" Request.ServerVariables.Get("AUTH_USER")
"ltbr/gt") End Sub
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The ASP.NET Page.Response Property

• Sends information to the browser
• Identifies the server and server properties
• IP address of the server
• Name and version number of the Web server
  software
• Cookies collection
• Sends cookies to the browser (to store or just
  hold for session)
• Status code
• Request was successful or encountered an error

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Redirection
Note ../updatePart.aspx is a relative address
that backs up 1 folder http//www.dave.com/updateP
art.aspx is an absolute address

• Going to a page the browser didn't ask for
• In response to a button click
• To an error page
• To a logon page
• Server can't just go to another page
• Asks the browser to redirect its request to
  another page
• Redirect to another page (addressed relative to
  the current page)
• Response.Redirect(updatePart.aspx)
• Redirect, passing values in a QueryString
• Response.Redirect(updatePart.aspx?partId789667"
  )

querystring being used to pass a field to next
program
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Web Services

• To access Future Shops catalog from your site
• You could post a link
• Also known as sending your user away
• You could scrape their web site
• Extracting data from the HTML they send
• They could provide a Web Service to their catalog
  application
• Web Services create business-to-business
  applications
• Exposes some of your programs over the Internet
• Source file has the extension .asmx
• Used like classes
• Public registry (UDDI)
• Registered public Web Services
• URL, what data they expect, what data they
  provide
• Third party Web Services are at
  http//www.xmethods.com

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Creating Web PagesCreating Hello World!

• David Turton
• Conestoga College
• Institute of Technology Advanced Learning
• www.conestogac.on.ca/dturton
• 1D17 X3610

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Terminology

• A project
• A complete web site or application system
• HTML templates, code, images, databases, etc.
• Contained in a folder named after the project
• Special projects Class libraries
• Centralised collection of classes (utilities)
• Referenced by multiple projects
• A solution
• Information about one or more projects
• Location, last forms you had open, etc.
• Disposable stuff
• Default location My Documents\Visual Studio 2008

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New ASP.NET Project (Web Site)Give it its own
home folder use Pascal notationEnsure the
language used will be Cnot on G ... Novell and
Microsoft don't get along
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ResultProject folder initial files created
Delete Default.aspx ... We'll recreate it later,
using a Master Page for layout.
.aspx
.aspx.cs
Project Folder Data Folder Default
ASP.NET web page C code file for above page
Note HTML source view or WYSIWYG design view
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Adding Web Forms to a Project
Can add a folder, Web Form, HTML page, CSS, XML
file/style, user control, master page, etc New
or Existing
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Hello World!

• Drop a label and a button on the page.
• Double-click the form
• In Page_Load routine
• put "Go ahead " message in label.
• Double-click the button
• In button's "Click" routine
• If "Go ahead" is in the label
• Change it to "Hello World!"
• Otherwise
• Change it to "Only once, please"

Yes, there's a trick to it
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Things to notice

• Control placement is clumsy
• Use lttablegt to manage layout
• Table rows push subsequent rows with them
• Use ltdivgt to manage layout
• With "float" and "width" style attributes
• Use HTML like ltbr /gt and ltpgt
• But we'll wean you off that...

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Things to notice

• You can't assign data directly to a control
• lblMessage "Hello World!"
• It's an "object"
• It has methods (procedures, functions)
• .Focus, .DataBind
• It has properties (attributes, characteristics)
• Which also have properties (.Length) and methods
  (.SubString)
• What do you want to change? Its colour? Its
  text?
• Specify the object the property to be affected
• lblMessage.Text "Hello World!"
• Or take a property and execute one of its
  methods
• lblMessage.Text.SubString(0,2)

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Viewing a Web Page

• Right-click on it in Design View
• Select view in browser

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Things to notice

• "only one click" never comes out
• Always get "Hello World!" message
• Use debug to explore this

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Debug setup- declare breakpoints - program
will stop before executing these lines
Click in border to set break-points
(first time debug is run)
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Debug at breakpoint- at each breakpoint, "F11"
to execute line-by-line- lines are highlighted
before they are executed- "F5" to just run to
the next breakpoint
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Debugging the code

• What you'll find
• Page_Load fires on every visit to the code
• Regardless of what event caused the visit
• But
• Want to change the label only on first load
• Try controlling this
• Boolean IsPostBack
• True is a post-back from an existing page
• False is initial load of the page

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Alternate debugging method

• Can throw comments out periodically
• Just "I'm here" stuff
• Or "the index is " gvCategory.SelectedIndex
• Insert following in your code
• System.Diagnostics.Debug.WriteLine("I'm here")
• Displays in VS.NET Output panel
• If running in debug mode