1. Beginning ASP.NET 4.5.1 in C# and VB Chapter 9
Validation
Beginning ASP.NET in C# and VB
Chapter 9

2. Objectives
You will be able to use validation controls on your web pages to validate user inputs automatically.

3. Validation Controls
Validation controls permit declarative validation of user inputs.
Specify conditions declaratively rather than writing code to check validity.

4. Validation Controls Overview RequiredFieldValidator RangeValidator
CompareValidator
RegularExpressionValidator
CustomValidator

5. Validation Controls
Each validation control is bound to a single input control.
One input control can have multiple validation controls.
Normally an invalid input will prevent the postback from being done.
Require user to provide valid inputs before passing them to the server.

6. CausesValidation Every button has a CausesValidation property.
Checked when button is clicked, before page is posted back.
If true, validation is performend on all input controls that have validation controls.
In the browser.
Again on the server.
If false, page is posted back without validation.

7. Why not do validation? Consider a Cancel button.
Sometimes we want to be able to do a postback even if some inputs are invalid.

8. Client-Side Validation
ASP.NET transparently provides JavaScript to do validation in the browser.
Supported by most modern browsers
Chrome
Firefox
Safari
Internet Explorer 5 and later
If client-side validation fails, page does not post back.
Error information is shown on the page.

9. Server-Side Validation
Even if page passes all validation checks on the browser, inputs will be validated on the server.
Hackers can easily bypass client-side validation.
Some users may disable JavaScript.
Client-side validation is a matter of convenience and performance only.
Not security.
Server-side code has the ultimate responsibility for ensuring that inputs are valid.

10. Simple Example Create a new empty ASPX C# website
Validation_Demo
Add new web form, Default.aspx
We will design a page with a TextBox having a range validator.
Second TextBox with no validator.

11. Design the Page Expand the Validation section of the Toolbox.
Add a RangeValidator beside the TextBox.

12. RangeValidator

13. Display Property Values
Static
Reserve space on page for the error message even if the control is valid.
Dynamic
Do not reserve space on page for the error message if the control is valid.
Useful when there are mulitple validators for a single control.
None
Do not display the error message.

14. Design the Page Add another TextBox with no validator.
Just so that we can tab out of the validated input.
Add an OK button.
btnOK
CausesValidation is true by default.
Add a label beside the button.
lblMessage

15. The Page in Design View

16. Add Click Event Handler
Double click on the button to add a Click Event Handler.

17. Page in Source View

18. Set Breakpoint Set a breakpoint on the Page_Load method.
So that we can tell when a postback occurs.

19. Program Running
Enter an invalid number and press tab

20. Error!
Ask google about it

21. Search Result: Unobtrusive Validation Mode

22. Search Result: Unobtrusive Validation Mode

23. Web.config
Add
Try again.

24. After User Presses Tab Key
Note that the page did not post back.

25. Server-Side Validation
To see how the page will work on a browser that does not support JavaScript set RangeValidator1.EnableClientScript property to false.
Try again.

26. After User Clicks OK Nothing happens when we tab out of the first box.
Error message is shown after postback when we click OK.

27. Server-Side Processing
Note that the error message appeared on the page, BUT
the click event handler executed even thought the input was invalid.
We can prevent the normal click actions if the page is invalid
but we have to provide an explicit check.

28. Server-Side Validity Check
protected void btnOK_Click(object sender, EventArgs e) {
if (Page.IsValid)
lblMessage.Text = "btnOK_Click event handler executed"; }
else
lblMessage.Text = "Input is invalid";
Try again with invalid input.

29. Invalid Input

30. Valid Input

31. No Input If nothing is entered, the range validation passes.
If we want to require input we need another validator.
RequiredFieldValidator

32. Add RequiredFieldValidator

33. RequiredFieldValidator Properties
Try it!

34. RequiredFieldValidator
Click on OK with no inputs.

35. Validation Summary
The validation summary control shows all error messages from the page together in one place.
Add a ValidationSummary below the OK button.
Modify the error messages to identify the input to which they apply.

36. Display Options Example:
If a validation control’s Text property is set, it will be shown at the position of the validator, and the ErrorMessage will be shown in the Error Summary.
Example:
Text: "This input is required"
ErrorMessage: "First input is required"

37. RangeValidator

38. RequiredFieldValidator

39. Validation Summary
Add a ValidationSummary at the bottom of the page.

40. Validation Summary
Try it!

41. Validation Summary

42. Summary Only
We might want to suppress the error message at the position of the input.
Avoid clutter with lots of validated inputs.
Set its Display property to None.

43. Display Property Set To None

44. Other Display Options
If a page has a lot of inputs, we might want to just flag the invalid inputs and put the detailed information in the summary.
Example:
Flag the input field with an invalid value.
Set Text to “*”
Set Display back to Static

45. Flag Invalid Input

46. Other Display Options

47. Other Properties of ValidationSummary
Border properties
DisplayMode
HeaderText
ShowMessageBox
EnableClientScript must be true.
ShowSummary
Set to false to disable summary

48. Validation Summary Properties

49. RangeValidator1

50. Validation Summary
End of Presentation