1. Unit 27 - Web Server Scripting
Week 2 Lesson 2 – Validation and Server Side actions

2. Previously…
Capturing User Information
Processing User Input

3. This Lesson
Validation
Server Side Processing

4. Validation Controls Form fields are completed
Values correspond to a particular format
Two fields contain the same value
Validation controls format – address
Within a particular range
Same value – password confirmation
The validation is automatically performed by the control and an error message issued if the validation fails. You do not have to do any coding – only set the correct control properties
Validation summary will provide of all the output from the validation control son a page. Can be useful for error checking.

5. Find the requiredfieldvalidator tool and drag to the web form

6. Using the Mailing list previous example -
Each of these controls are set up by setting the relevant properties.
Each control has a ControlToValidate property
ErrorMessage property, etc
For the regular expression validator – set the ValidateExpression property by clicking on the … to the right of the box. This displays a list of the preset expression for you to choose from eg phone numbers, etc.
NOTE – all it can check is that the format matches the one selected.

7. Using the Mailing list previous example -
Now we have a table of three columns (use the layout tab to add columns or rows to a table)

10. How ASP.NET works…. User requests a page
Request is sent to the web server
Web server –
If pure HTML then page returned to user
If ASP.NET then server processes page
User receives HTML page.
User requests a page either by typing it in on the address bar of a browser or by clicking a link on a page.
Important point –
HTML is rendered by the browser on the user’s machine. All the server sends back is a stream of text.
Request is sent to the web browser hosting that page.
Web server –
If pure HTML then page returned to user
If ASP.Net then server processes page. This means that ASP.NET will examine the page and see if there is anything it needs to do. This is defined as Server Side Processing as it is happening on the server. The end result of the processing is HTML which is sent back to the user.
User receives the HTML page and the browser examines the HTML and shows the page with all the formatting – this is called rendering.

11. Server-side Processing
Statelessness
Nothing is maintained in code between page loads
Only refers to standard HTML elements & code
Postback
Information from a control is posted back to the server
ASP.NET runs the control and it posts back to browser
Server-side events
Events are actions that take place when something or someone interacts with a web page
Page load event
Statelessness – loading a page the first time is different from loading it a second time. ASP.Net has no knowledge of the previous times the page has been loaded.
Example – a site where the user logs in. first time user message says ‘Welcome stranger, please login.
Second time page loaded message should say ‘welcome’ & User Name
ASP.Net assumes they are separate pages so you have to check each time the page loads to see whether the user is logged in for example.
Statelessness does not refer to Web controls as these have an inbuilt ability to retain their values each time a page is requested.
Postback – think of it in terms of a letter being posted to ASP.NET which then writes a new letter back to you and so on…
The postback causes the page to be sent to ASP.NET, which runs thru any processing it needs to and sends the resultant HTML back to the user. The process is the same every time the page is loaded. It has no knowledge of whether the page was loaded before.
Events are actions that take place when something or someone interacts with a web page. EG when a button is clicked, an event is generated or RAISed. There is an events button at the top of the properties box for each control.
Page load event can be used to detect whether the page has been loaded before by using the IsPostBack property.

12. Page Load Event
Select the “code-behind” tab to show the “code-behind” window.
Choose “page-events” from the left hand drop-down list.
Choose “Load” from the right-hand drop-down list to display the page load event sub routine. Any actions you want performed on page load can be entered here and will be run each time the page is loaded.

13. Make a new web page
Add the following in order:
Button
Label

14. Double Click the Button
Add the following code:
Label2.Text = "The button has been clicked"

15. Double Click the Page Add the following code to the pageLoad event:
If Page.IsPostBack Then
Label1.Text = "The page has been loaded because of a button click"
Else
Label1.Text = "The page has loaded for the first time"
End If
Label2.Text = ""

16. Detecting Postback
This is an example of loading a page and detecting postback.
The ispostback property is true if the page is being redisplayed, as in the case of a button click. For the first time ispostback is false.

17. When you try to refresh the page, a message is displayed

18. Server Side Example Panel LinkButton Why not a HyperLink?
Rectangular area
Visibility controlled server side
LinkButton
Click method
Returns to same page
Why not a HyperLink?
Goes to any web page including current one
No Click method
There is a server-side webform control called a "Panel." A Panel is a rectangular area on your HTML page, the visibility of which can be controlled on the server side.
"LinkButton," which is essentially a hyperlink, but can be made to behave like a button via the Click server-side method.
Why am I using a LinkButton instead of a hyperlink? The implication of a hyperlink is that you are free to go to any Web page, including the current one. But there is no implication that I want to return to the same page while altering parts of that page. In addition, there is no server-side, convenient method like Click available with a hyperlink.
The LinkButton control offers the look and feel of a hyperlink, but with two other benefits, namely:
The intention of coming back to the same page when pressed.
The convenient method of Click.

19. Add a Panel Start a new website Add a panel to the first div
Press the right arrow key and the press enter twice
Add two more panels in this way
In panel 1 type:
An example of a panel that is going to disappear
Change the panel ID to testPanel1
In panel 2 type:
Enter your password
Change the panel ID to testPanel2
In panel 3 add a button and change the text to:
Enter
Change the panel ID to testPanel3

20. Add a link Below the div add the following: A link button
Change the text to:
Click Me!!

21. Double Click the Link Button
Add the following code to the linkButton section:
If TestPanel1.Visible Then
TestPanel1.Visible = False
Else
TestPanel1.Visible = True
End If

22. The idea is that once you set the panel visibility to "false," the entire HTML segment will disappear from view.
Every control on your page is represented as a .NET object on the server side. Moreover, the state of these objects (or controls) is maintained between multiple round trips to the server. This allows you to respond to events either on the client or on the server side. While responding to events on the server side, rest assured that when the page is repainted, all of its internals will repaint as if nothing had happened.

24. Tutorial