Validating User Input with VB. NETIntroduction. Validating user input can be quite a pain, especially if you do not know what techniques and what namespaces are at your disposal. Because everyone has a different way of doing things, my methods might not be 1.
This is why I decided to make use of Regular Expressions here within this article. Today you will learn how to use regular Expressions to validate user input. What is Validation? In simple terms, validation refers to ensuring entered data is well, valid.
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Determining whether or not data is valid can sometimes be a painstaking process as there are numerous tests that need to be thought of. These tests include: Format test - This test determines if the entered string is in the correct format. Type test - This test checks if the input is the correct type.
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For example: Integers of dates that do not need conversion afterwards. Permitted Character test - This test ensure that no illegal characters are entered. For example: If a user is supposed to enter a name, numbers and some special symbols must not be allowed. Range test - This tests checks to see if entered values are within a specified range. For example : If you are only supposed to type in 5.
Also, the more tests you are performing, the slower your app might become. The answer is simple: Use Regular Expressions! That is what they were invented for.
What are Regular Expressions? Regular Expressions are extremely powerful. They make use of a pattern matching system to match the input with a certain pattern of data. This means that as a programmer, you have the power to supply the exact pattern for the input you desire in any text input field. By using Regular Expressions this way, you can reduce the chances of getting errors at erratic times. For more information regarding Regular Expressions, you are welcome to look at these two MSDN articles: An Example Project. 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.
Start Visual Studio and create a Desktop VB. NET application and design the form to resemble Figure 1. Figure 1 - Our Design. Code. The Regular Expression's functionalities exist in the System. Text. Regular. Expressions namespace, so let us add that first: Imports System. Text. Regular. Expressions ' Regular Expressions Namespace. Add the following four variables inside the General Declarations section: Private Name.
Valid As Boolean 'Is Name Valid? Based on each of these variables' values, we will know if the data is correct or not. Validating Names. A name doesn't generally contain weird symbols, and definitely not numbers. That may seem like Captain Obvious speaking, but you'll be amazed at some of the data that gets entered into a name field. Sometimes people are just trying to be funny, or they are literally trying to break your program.
You could say that a program's testers are supposed to do this; yes, they should - nobody else should. Add the following inside your name Textbox's Leave event: Private Sub txt. Name. The Leave event fires when the control loses focus. This can be from the mouse clicking inside another field, or a Tab key being pressed to navigate to the next input control. If the data is indeed only alphabetic letters (no symbols, no numbers or any other punctuation characters) the test succeeds and stores True inside the Name. Valid variable. If not, if there is even just one unallowed character that is not supposed to be there, the Match method will return False. See how quick it is to use Regular Expressions?
Instead of you having to loop through each character to determine what that character is, you simply need the correct Regular Expression pattern. If you are uncertain about the pattern I supplied, have a look here. Validating Surnames. Well, the same logic should obviously apply here.
Just a note, some surnames contain spaces and even hyphens. My surname contains a space and it can get quite frustrating if I am not allowed to enter my correct surname, or that I have to edit my surname not to include a space. So, what I am trying to say is: make sure you understand other cultures, or be aware of people with uncommon names. Add this to validate the surname textbox: Private Sub txt. Surname! Phone numbers usually follow some sort of format. This is because it becomes more legible than just a normal set of numbers. People expect to enter a phone number in a format similar to this: ###- ###- ####.
Sometimes there are even brackets surrounding the code. In certain cases the international dialling code will also need to be supplied.
Using Regular expressions here, is basically the standard, even though it is a bit messy. 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 = . This function is later called inside the textbox's Lost. Focus event, which also fires when a control loses the focus. I set up my Expression to allow only numbers, but in the format I explained earlier. 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.
Validating Emails. This one will be tough, be warned. Emails also follow a certain format.
It is always username at sub domain dot domain. Keep in mind that each country has its own domain name, which sometimes will look like: . The point I am trying to make is that there may be more than one dot after the at sign.
Add this code to validate the Email textbox: Private Sub Validate. Email(). 'Set Up Reg Exp Pattern To Allow Most Characters, And No Special Characters. Dim re. Email As Regex = New Regex(. It just summarizes the above paragraph. Each email must have an @ sign.
Each email must have at least one . Again, certain special characters are obviously not allowed. This sub checks the email's format and if it thinks that it matches, it returns True and vice versa. Obviously this only works for the formatting of the email.
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 Registration confirmation of some sorts. Conclusion. As you can see, Regular Expressions are a vital tool to have at your disposal, so become good friends with them. I hope you have learned from this article and that you have enjoyed it as much as I did.
Until next time, cheers!