user input validation

7/25/2019 User Input Validation

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User Input ValidationVisual Basic .NET


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ValidationValidationrefers to ensuring entered data is well, valid.

Validation helps avoid bugs by filtering out invalid data toget in to the program flow.


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Basic Validation Process

Format test- This test determines if the entered string is in thecorrect format.

Type test- This test checks if the input is the correct type. Forexample: Integers of dates that do not need conversion afterwards.

Permitted Character test - This test ensure that no illegalcharacters are entered. For example: If a user is supposed to entera name, numbers and some special symbols must not be allowed.

Range test- This tests checks to see if entered values are within aspecified range. For example : If you are only supposed to type in50 characters, you must not be able to enter more than fifty.


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Regular Expressions Provide a powerful, flexible, and efficient method

for processing text.

Enables you to quickly parse large amounts of textto find specific character patterns;

To validate text to ensure that it matches a

predefined pattern (such as an e-mail address);


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Regular Expressions To extract, edit, replace, or delete text substrings;

and to add the extracted strings to a collection in

order to generate a report.


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RegEx Example - Replacing

SubString!"#$%&')*'&+",-+.&,/+0123%4.#%+''5$6'7$812+4.3"#2+

91:25;)1:73565"#3&&+%6 ?')&%560@ A5"63"+'


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RegEx - Identifying

Duplicate Words!"#$%&')*'&+",-+.&,/+0123%4.#%+''5$6'7$812+"$87356

91:25;)1:73565"#3&&+%6 ?')&%560@ AB:


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RegEx

The regular expression pattern B:


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RegEx Methods The Regex.Matchesmethod is called with regular

expression options set to

RegexOptions.IgnoreCase. Therefore, the match

operation is case-insensitive, and the exampleidentifies the substring "This this" as a duplication.

Note that the input string includes the substring

"this? This". However, because of the interveningpunctuation mark, it is not identified as a

duplication.


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Guided Example Start Visual Studio and create a Desktop VB.NET

application and design the form to resemble this

figure.


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ExampleImportsSystem.Text.RegularExpressions' Regular Expressions Namespace

PrivateNameValidAsBoolean'Is Name Valid?Private SurnameValid As Boolean 'IsSurnameValid?PrivatePhoneValidAsBoolean'Is Phone Number Valid?Private EmailValid As Boolean 'IsEmailValid?


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Private Sub txtName_Leave(sender As Object, e As System.EventArgs) HandlestxtName.Leave

'If Not A Matching Format Entered If Not Regex.Match(txtName.Text, "^[a-z]*$",

RegexOptions.IgnoreCase).Success Then 'Only Letters

MessageBox.Show("Please Enter Alphabetic Characters Only!") 'InformUser

txtName.Focus() 'Return Focus txtName.Clear() 'Clear TextBox

NameValid = False 'Boolean = False

Else

NameValid = True 'Everything Fine

End If

End Sub


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PrivateSubtxtSurname_Leave(sender AsObject,e AsSystem.EventArgs)HandlestxtSurname.Leave

'Create A Pattern For Surname Dim strSurname As String = "^[a-zA-Z\s]+$"

Dim reSurname As New Regex(strSurname) 'Attach Pattern To Surname Textbox

'Not A Match If Not reSurname.IsMatch(txtSurname.Text) Then

MessageBox.Show("Please Enter Alphabetic Characters Only!")

txtName.Focus()

txtName.Clear()

SurnameValid = False

Else

SurnameValid = True

End If

End Sub


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'Function To Check Phone Number Validity Public Function ValidatePhone(ByVal strPhoneNum As String) As Boolean

''Create Reg Exp Pattern Dim strPhonePattern As String = "^[1-9]\d{2}-[1-9]\d{2}-\d{4}$"

'CreateRegExObject DimrePhone AsNewRegex(strPhonePattern)

'Something Typed In If Not String.IsNullOrEmpty(strPhoneNum) Then

PhoneValid = rePhone.IsMatch(strPhoneNum) 'CheckValidity

Else

PhoneValid=False'Not Valid / Empty

End If

Return PhoneValid 'ReturnTrue/False

EndFunction

PrivateSubtxtTel_LostFocus(sender AsObject,e AsSystem.EventArgs)HandlestxtTel.LostFocus

IfNotValidatePhone(txtTel.Text)Then'Call Phone Validation Function

MessageBox.Show("Please Enter Phone Number In Correct Format!")

txtTel.Clear() 'ClearInput txtTel.Focus()'Return Focus

End If

End Sub


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PrivateSubValidateEmail()

'Set Up Reg Exp Pattern To Allow Most Characters, And No Special Characters Dim reEmail As Regex = New Regex("([a-zA-Z0-9_\-\.]+)@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\." + _ ")|(([a-zA-Z0-9\-]+\.)+))([a-zA-Z]{2,4}|[0-9]{1,3})", _ RegexOptions.IgnoreCase _ Or RegexOptions.CultureInvariant _ Or RegexOptions.IgnorePatternWhitespace _ Or RegexOptions.Compiled _

)

Dim blnPossibleMatch As Boolean = reEmail.IsMatch(txtEmail.Text)

If blnPossibleMatch Then

'CheckIfEnteredEmailIsInCorrectFormat IfNottxtEmail.Text.Equals(reEmail.Match(txtEmail.Text).ToString)Then

MessageBox.Show("Invalid Email Address!")

Else

EmailValid=True'Email is Perfect

End If

Else 'NotA MatchToPattern

EmailValid=False'Set Boolean Variable To False

MessageBox.Show("Invalid Email Address!") 'InformUser

txtEmail.Clear()'Clear Textbox

txtEmail.Focus() 'SetFocusToTextBox

EndIf

EndSub

PrivateSubtxtEmail_LostFocus(sender AsObject,e AsSystem.EventArgs)HandlestxtEmail.LostFocus

ValidateEmail()'Check Email Validity

End Sub


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References:

MSDN

Code guru

user input validation

Documents