Web Controls

1
Web Controls
2
Outline

• Processing Web Controls
• For Each Loop
• Postback

3
More on Class

• Class is a blueprint for which objects are
  created
• Class inheritance
• It allows one class to acquire all the properties
  and methods of the parent class
• Partial class
• It allows you to split a single class into more
  than one file

4
Default.aspx

• lt_at_ Page Language"VB" AutoEventWireup"false"
  CodeFile"Default.aspx.vb" Inherits"_Default" gt
• lthtml xmlns"http//www.w3.org/1999/xhtml" gt
• lthead runat"server"gt
• lttitlegtIndex Pagelt/titlegt
• lt/headgt
• ltbodygt
• ltform id"form1" runat"server"gt
• ltdivgt
• ltaspLabel ID"Label1" runat"server"
  Text"Enter Name"gtlt/aspLabelgt
• ltaspTextBox ID"TextBox1" runat"server"
  gtlt/aspTextBoxgt
• ltaspButton ID"Button1" runat"server"
  Text"Submit" /gt
• lt/divgt
• lt/formgt
• lt/bodygt
• lt/htmlgt

5
Default.aspx.vb

• Partial Class _Default Inherits
  System.Web.UI.Page
• Protected Sub Button1_Click(ByVal sender As
  Object, ByVal e As System.EventArgs) Handles
  Button1.Click
• TextBox1.Text "Here is some sample
  text."
• End Sub
• End Class

6
Procedures

• Subroutines or sub-procedures do not return
  values
• Create a Subroutine
• Declared using the keyword Sub
• Exit sub statement to exit the subroutine
• End with the keywords End Sub

7
Event Procedure

• An event procedure is not executed until an event
  triggers the event procedure
• An event procedure does not return a value
• The Page_Load event procedure is triggered when
  the page is loaded into the browser

8
Page Events

• The Page object consists of a variety of methods,
  functions, and properties that can be accessed
  within the code behind the page
• The first time a page is requested by a client, a
  series of page events occurs
• The first page event is the Page_Init event which
  initializes the page control hierarchy
• The Page_Load event loads any server controls
  into memory and occurs every time the page is
  executed

9
simple.aspx

• lt_at_ Page Language"VB" AutoEventWireup"false"
  CodeFile"simple.aspx.vb" Inherits"simple" gt
• lthtml xmlns"http//www.w3.org/1999/xhtml" gt
• lthead runat"server"gt
• lttitlegtUntitled Pagelt/titlegt
• lt/headgt
• ltbodygt
• ltform id"form1" runat"server"gt
• ltdivgt
• lt/divgt
• lt/formgt
• lt/bodygt
• lt/htmlgt

10
simple.aspx.vb

• Partial Class simple Inherits System.Web.UI.Page
• Protected Sub Page_Load(ByVal sender As
  Object, ByVal e As System.EventArgs) Handles
  Me.Load
• Response.Write("This is my first line of
  ASP.NET program. ltbrgt")
• Response.Write("More to come next week.
  ltbrgt")
• End Sub
• End Class

11
Textbox

• ltasptextbox id"txtName" runat"server " /gt
• Code to retrieve the value of the textbox
• Dim name as String txtName.Text

12
Drop-down List

• ltaspdropdownlist id"list1" runat"server"gt
• ltasplistitem Selected"True"gtMadridlt/asplisti
  temgt
• ltasplistitemgtOslolt/asplistitemgt
• ltasplistitemgtLisbonlt/asplistitemgt
• lt/aspdropdownlistgt
• Code to retrieve the value of a selected item
• Dim city as String list1.SelectedItem.Value
• Syntax to retrieve a property value of an object
• objName.PropertyName

13
Radio Button

• ltaspradiobuttonlist id"fare" runat"server"gt
• ltasplistitem runat"server" value"First
  class" Selected"True" /gt
• ltasplistitem runat"server" value"Coach"
  /gt
• lt/aspradiobuttonlistgtltbr /gt
• Code to retrieve the value of a radio button
• Dim fareclass as String fare.SelectedItem.value
  

14
ListItem class

• Property
• Count -- the number of items
• Selected -- Gets or sets a value indicating
  whether the item is selected
• Text -- Gets or sets the text displayed in a list
  control for the item represented by the ListItem
• Method
• Add(ListItem) -- adds a list item

15
For Each Loop

• Loop through the items in a set of data
• Dim lstItem as ListItem
• For Each lstItem In chklst.Items
• Next

16
Postback

• The process of posting data back to a form is
  known as postback
• All web controls support postback by default
• The values that are stored with the page remain
  with the page

17
Auto Postback

• It means that the control will have a post back
  immediately when it detects a user action

18
Page.IsPostBack

• Page default object
• Belongs to web page class
• IsPostBack
• A property of the web page class
• Boolean variable
• False when the page is displayed the first time
• True the page is being redisplayed in response
  to a control event

19
Web.config

• Upload and store the file at your folder on the
  server
• It can control error message display
• The following web.config will allow error
  messages to be displayed
• lt!-- Web.Config Configuration File --gt
• ltconfigurationgt
• ltsystem.webgt
• ltcustomErrors mode"Off"/gt
• lt/system.webgt
• lt/configurationgt