Validation

1
Validation

• Validating Control Values
• Server-side and Client-side Validation

2
What is Validation?

• It is often important to validate the contents
  entered on a Web form before trying to process
  those contents.
• Validation may include tasks such as
• Ensuring a text field is not empty
• Ensuring that a selection has been made
• Ensuring that a value is in a certain range
• Ensuring that the structure of an entry is
  permissible (e.g., a value entered for a social
  security number has the form ddd-dd-dddd).

3
Where Should Validation Occur?

• Since server-side operations require a post-back
  with its round-trip to the server and back to the
  client, it is more efficient to do some
  validation on the client.
• For example, if a form contains 10 fields that
  must be completed (non-empty), it is more
  efficient to verify that all 10 contain data
  before permitting a post-back than to do up to 10
  post-backs as each field is skipped.
• This type of validation requires execution of
  client-side JavaScript or VBScript.

4
Server-side Validation, too

• It is important to do server-side validation in
  addition to client-side validation because
• Client browser may not support script execution.
• Security restrictions on the client may prevent
  script execution even if browser supports it.
• A malicious user can subvert client-side
  validation, possibly permitting bad things to
  happen on server if it does not also check for
  valid data input.
• Web Forms support server-side validation through
  numerous validation controls and their ability to
  interact with data entry controls such as
  TextBoxes.

5
Web Forms Validation Controls

• The following .NET validation controls are
  provided for Web Forms
• RequiredFieldValidation verify that a required
  input field is not empty
• RangeValidator verify that a value is in a
  specified range
• CompareValidator compare value of a control
  with constant or with value of another control
• CustomValidator user supplied validation
  algorithm
• RegularExpressionValidator match value of a
  control against a pattern using a regular
  expression
• ValidationSummary Collection of messages from
  all validation controls on a page

6
Web Forms Validation Controls

• Validation controls only apply to controls that
  define a single value to validate.
• Controls such as DataGrids cannot be validated
  using the validation controls.
• Controls that can be validated
• HTMLInputText
• HTMLTextArea
• HTMLSelect
• HTMLInputFile
• TextBox
• DropDownList
• ListBox
• RadioButtonList

7
Web Forms Validation Controls

• Web Forms Validation Controls provide both of the
  following
• Client-side validation through JavaScript if
  the client browser supports JavaScript and if the
  clients security permits script execution. Post
  Backs may be prevented until client-side
  validation succeeds.
• Server-side validation following a Post Back
  using standard .NET events, properties, and
  methods

8
Common Ideas in Validation

• Often, a message, symbol, or other output is
  placed next to a control with invalid data.
• May be a contrasting color to call visual
  attention to it
• If symbol, messages may appear in a MessageBox or
  in a summary list elsewhere on the page
• Often multiple types of validation are needed for
  a single input control.
• For example, a required numeric field needs to be
  evaluated for being non-empty and for having a
  value in the proper range using different
  validation controls.
• Different error messages are used to accompany
  the different types of errors.

9
Using a Validation Control

• Commonly, place a validation control on a form
• Next to the control it is to validate
• Where you want the error message or error
  indicator to be displayed
• Validation control typically has a
• ControlToValidate property identifying which
  control it validates
• ErrorMessage text to display or to place in the
  error summary
• Initial value (may be empty, indicating no
  display if valid data is entered).
• Text Text to display in place, if the
  ErrorMessage is displayed in Summary.

10
Validation Control Display Property

• Indicates whether the control occupies space on
  the visible form when no error has been detected
• Static always occupies space even if hidden
• Dynamic occupies space if error useful if
  multiple validation types (e.g., required and
  range) are needed so that only the one
  appropriate message will occupy the space next to
  control with the invalid value.
• None never occupies space
• used if the message is only to appear in Summary,
  for example

11
RequiredFieldValidation Control

• Used to determine whether the associated control
  has no value. For example
• Empty TextBox
• Nothing selected in ListBox
• This is especially important because all other
  controls validate an empty field (or unselected
  item) as being valid
• Often used with other validation controls
• Used to prevent a post-back until all required
  fields are filled/selected

12
RangeValidator Control

• Used to verify a value is in proper range.
• Properties include
• Type of data
• MinimumValue, MaximumValue
• ControlToValidate
• ErrorMessage message to display
• Text Symbol/text to use where RangeValidator
  control is when ErrorMessage is placed in Summary
• Tooltip

13
Data Types Supported

• Data types supported by RangeValidator and
  CompareValidator
• String
• Integer
• Double
• Date
• Currency - Specifies a monetary data type

14
CompareValidator

• Compare one controls value with another
  controls value or with a constant.
• Properties include
• Data Type
• ControlToCompare
• ValueToCompare
• ControlToValidate
• ErrorMessage
• Text
• ValidationCompareOperator

15
ValidationCompareOperator

• Equal
• NotEqual
• GreaterThan
• GreaterThanEqual
• LessThan
• LessThanEqual
• DataTypeCheck
• A data type comparison of the value entered into
  the input control being validated and the data
  type specified by the BaseCompareValidator.Type
  property.
• Validation fails if the value cannot be converted
  to the specified data type.
• Note   The ControlToCompare and ValueToCompare
  properties are ignored when this operator is used.

16
RegularExpressionValidator

• Used to verify that the form of input data is
  correct by using pattern matching.
• Can verify that a telephone number, social
  security number, e-mail address, URL, or similar
  item is formatted correctly and could be valid.
  
• It does not guarantee that the input is valid
  only that its format is valid.

17
RegularExpressionValidator

• Some important properties of a RegularExpressionVa
  lidator control
• ControlToValidate
• ToolTip
• ErrorMessage
• Text
• ValidationExpression a regular expression
  describing the pattern to be used as the input
  value is checked for a match with the pattern

18
RegularExpressionValidator

• Some common items are provided and can be
  selected from a combo box
• Other resources for regular expressions include
• Regulator at http//regex.osherove.com/
• Expresso at http//www.ultrapico.com/Expresso.htm

19
Some Regular Expression Characters
20
CustomValidator

• If you wish to provide your own validation
  algorithm, use a CustomValidator.
• In this case, you should provide both the
  JavaScript client-side algorithm and the .NET
  server-side event handler.
• Details not covered here.

21
ValidationSummary Control

• This control can be used to display all error
  messages gathered from other validation controls
  that failed validation.
• Can be displayed in list, bulleted list, or
  paragraph format.
• Alternatively, can be displayed using
  MessageBox-like window.

22
ValidationSummary Control
 
 
ValidationSummary Control showing MessageBox
Text property of RequiredFieldValidator
ValidationSummary Control Contents are the
ErrorMessages from the individual controls
23
IsValid Property

• The base class for validation controls has a
  property named IsValid. It is set to false if
  the associated control does not pass validation.
• The Page class contains an IsValid property that
  is set to false if any validation controls
  IsValid property is false.
• On server-side, if a control fails to pass
  validation, the ONLY THING that happens is
  IsValid is set to false.
• Remember, if client-side validation is performed,
  the post-back is blocked until validation passes.
• If client-side validation is not performed, this
  becomes important.
• Remaining code is executed normally. To prevent
  unwanted actions, check the IsValid property in
  subsequent event handler(s).
• If Me.IsValid Then
• Take some action
• End If

24
Validate Method

• Each validation control has a Validate method
  that performs the designated validation.
• Each Page has a Validate method that cycles
  through all validation controls on the Page and
  invokes their Validate methods.
• Page.Validate() is normally invoked AFTER
  Page_Load but before other user-related events
  such as a button click event.
• IsValid is only meaningful after Validate is
  called.
• One may call Validate manually for any of the
  validation controls individually or for the
  entire Page if necessary.