WebForm

1
WebForm

• Objective
• Web aspx flow sequence
• Common Control color alignment
• Response.write/ redirect, server transfer
• Page object
• Session variable
• View State.
• ArrayList HashTable

2
Executing .ASPX
3
WebServer Controlvs HTML Control

• Webserver controls run on the server.
• E.g. you can program a server button as before.
  (double click to get the button_click event.)
• But you cannot program a HTML button.
• Also, the HTML table cannot be access in VB. i.e.
  you cant get me.table1 (Alignment must be done
  using HTML)

4
DropDownList

• ComboBox replaced by DropdownList.
• To get the selected value use
• Dropdownlist1.selecteditem.text (different from
  combobox).
• use the AutoPostBack property
• to choose how to handle
• selectedindexchange
• Post page to server
• Ignore indexchange..

5
RadioButtonList

• To show a list of radiobuttons
• Use the items collection to add buttons and text.
• Use the
• SelectedIndexChanged
• sub to get selected item
• ResponseWrite(Me.RadioButtonList1.SelectedItem.Te
  xt)

6
Use of Panel and PlaceHolder

• Use of panel and placeholder to hold other
  controls.
• Place buttons and textboxes in panel and make
  them visible or otherwise.
• Me.panel1.visible true / false.
• Home work investigate PlaceHolder.

7
Response.Write/Redirect

• Response.Write writes a message to the client
  browser. E.g. response.write(Hello)
• E.g. response.write ( ltigt Crazy crazy lt/igt)
  sends an italic Crazy crazy to the browser.
• Response.redirect redirect to another page.
• E.g. jump to another page with
• reponse.redirect(webform2.aspx)

8
Page.IsPostBack

• An .aspx is repeatly called by the brower.
• Th form_load event in windowapplications, only
  run once when the form is loaded.
• The page_load sub is run everytime the .aspx is
  called
• To tell whether the page is called the first time
  or subsequent times Use the page.Ispostback
• page.Ispostback means 2nd,3rd,4th .. Times.
• If not page.Ispostback then checks 1st time.

9
PageLoad Initialization

• Perform initialization work once in page load.
  For example initialize listbox fill dataset.
• Sub Page_load (..
• If not page.IsPostBack then
• RadioButtonList1.Items.Add("aa")
• RadioButtonList1.Items.Add("bb")
• me.dbProd.Fill(dsProd1)
• session(dsProduct) dsProd1
• End if
• End sub

10
Keeping state with session var.

• As each time the page is reloaded all data is
  lost.
• When transferring to another page, you need to
  keep track of info such as login id or datasets.
• Use the session variables to keep data while the
  session is running.

11
Session Variables

• To create a session variable, in webform1
• session(loginID) S001
• To retrieve the session variable in webform2
  user session(loginID)

webform2
webform1
session(loginID) S001
Dim user as string User session(loginID)
12
Session variable (Counting)

• Dim ing a global variable to Count will NOT
  work in webform.
• count is redim to 0 everytime
• the page is reloaded.
• Label will always show
• 1, no matter how many
• times the button is
• clicked.
• Soln Use session(count) 1.

Dim count as integer Sub button1_click(.
count count 1 label1.text count End Sub
button2_click(. session(count) 1
label1.text count end
13
Session Var. and Redirect

• Session variable is used to keep variables alive
  between page loads and page jumps.
• BUT it does NOT always work with
  response.redirect.
• Instead use Server.transfer
• e.g. Server.Transfer(webform2.aspx)

14
Keeping value with ViewState

• As webpages are stateless, on every page reload,
  the textbox values should disappear. The values
  in textboxes are kept using the viewstate
  EnableViewState True.

15
ArrayList

• ArrayList functions similarly to Listbox.
• Dim pass as New Arraylist
• pass.Add("111")
• pass.Add("222")
• pass.Add("333")
• ArrayList has properties
• Sort, reverse, count,
• Contain, insert, .

16
HashTables

• Store passwords in Hashtable
• Dim hash as new Hashtable
• hash.Add("S001", "111")
• hash.Add("S002", "222")
• hash.Add("S003", "333")
• hash.Add("S004", "444")
• hash.Add("S005", "555")
• To get password for S003 use hash(S003)

17
Moving Applications

• After you move a webapplication folder.
• Right-click on the folder and select sharing
• Choose web-sharing tab.
• Start IIS.
• Turn off the proxy using -- IE5 ?Tools ?
  InternetOptions ? Connections ? LanSettings
• Click on the project to run.