Is Match(str Phone Num) 'Check Validity Else Phone Valid = False 'Not Valid / Empty End If Return Phone Valid 'Return True / False End Function Private Sub txt Tel_Lost Focus(sender As Object, e As System. If it isn't valid input, it will clear the textbox and give it the focus again; if it is valid, the Phone Valid variable gets updated to true. This does have a list of possible values but also allows for editing. Add this to validate the surname textbox: Private Sub txt Surname_Leave(sender As Object, e As System. Leave 'Create A Pattern For Surname Dim str Surname As String = "^[a-z A-Z\s] $" Dim re Surname As New Regex(str Surname) 'Attach Pattern To Surname Textbox 'Not A Match If Not re Surname. Add the following code to validate your phone number textbox: 'Function To Check Phone Number Validity Public Function Validate Phone(By Val str Phone Num As String) As Boolean ''Create Reg Exp Pattern Dim str Phone Pattern As String = "^[1-9]\d-[1-9]\d-\d$" 'Create Reg Ex Object Dim re Phone As New Regex(str Phone Pattern) 'Something Typed In If Not String. This function is later called inside the textbox's Lost Focus event, which also fires when a control loses the focus. Keep in mind that each country has its own domain name, which sometimes will look like: Private Sub Validate Email() 'Set Up Reg Exp Pattern To Allow Most Characters, And No Special Characters Dim re Email As Regex = New Regex("([a-z A-Z0-9_\-\.] )@((\
This is why I decided to make use of Regular Expressions here within this article.For details about the makeup of event handlers, see Event Handlers Overview.The Form and Control classes expose a set of events related to application startup and shutdown.Also, the more tests you are performing, the slower your app might become. For more information regarding Regular Expressions, you are welcome to look at these two MSDN articles: Because it is always easy to learn by doing things practically, you will be creating an app that makes use of Regular Expressions to determine valid input. NET application and design the form to resemble Figure 1. Obviously this only works for the formatting of the email.Figure 1 - These objects will determine if all our data is valid or not. Clear() 'Clear Text Box Name Valid = False 'Boolean = False Else Name Valid = True 'Everything Fine End If End Sub Easy one to start with. Focus() 'Set Focus To Text Box End If End Sub Private Sub txt Email_Lost Focus(sender As Object, e As System. Lost Focus Validate Email() 'Check Email Validity End Sub The expression may look horrible to the layman's eye, but look closer. To check if the user has entered an email that actually exists, you will have to find a different way such as to send a of some sorts.