How to Validate a Registration Form Using Regular Expression in C#

Submitted by janobe on Friday, July 22, 2016 - 09:15.
In this tutorial, I will teach you how to validate a Registration Form using Regular Expression in C#. With this method, you can restrict all the textboxes in a form.It is also a guide for all users when they're going to fill up a registration form.

Let’s get started:

Open Microsoft Visual Studio 2008 and create new Windows Form Application for C#. Then, do the following Form as follows. fig 1 Go to the Solution Explorer, click the “View Code” to make the code editor appear. fig 2 In the code editor, put the "using System.Text.RegularExpressions;" above the namespace to access regular expression library. 
  1. //import the regular expression library
  2. using System.Text.RegularExpressions;
After that, do the following codes for formating the specific fields using the correct pattern. 
  1. //initialize the validating method
  2.             static Regex Valid_Name = StringOnly();
  3.             static Regex Valid_Contact = NumbersOnly(); 
  4.             static Regex Valid_Password = ValidPassword();
  5.             static Regex Valid_Email = Email_Address();
  6.  
  7.  //Method for validating email address
  8.         private static Regex Email_Address()
  9.         {
  10.             string Email_Pattern = @"^(?!\.)(""([^""\r\\]|\\[""\r\\])*""|"
  11.                 + @"([-a-z0-9!#$%&'*+/=?^_`{|}~]|(?<!\.)\.)*)(?<!\.)"
  12.                 + @"@[a-z0-9][\w\.-]*[a-z0-9]\.[a-z][a-z\.]*[a-z]$";
  13.  
  14.             return new Regex(Email_Pattern, RegexOptions.IgnoreCase);
  15.         }
  16.         //Method for string validation only
  17.         private static Regex StringOnly()
  18.         {
  19.             string StringAndNumber_Pattern = "^[a-zA-Z]";
  20.  
  21.             return new Regex(StringAndNumber_Pattern, RegexOptions.IgnoreCase);
  22.         }
  23.         //Method for numbers validation only
  24.         private static Regex NumbersOnly()
  25.         {
  26.             string StringAndNumber_Pattern = "^[0-9]*$";
  27.  
  28.             return new Regex(StringAndNumber_Pattern, RegexOptions.IgnoreCase);
  29.         }
  30.         //Method for password validation only
  31.         private static Regex ValidPassword()
  32.         {
  33.             string Password_Pattern = "(?!^[0-9]*$)(?!^[a-zA-Z]*$)^([a-zA-Z0-9]{8,15})$";
  34.  
  35.             return new Regex(Password_Pattern, RegexOptions.IgnoreCase);
  36.         }
Go back to the design view, double-click the button and do the following codes to validate the registration form. 
  1. //Validate all textboxes when the button is clicked
  2.  
  3.         private void btnSave_Click_1(object sender, EventArgs e)
  4.         {
  5.  //for Name 
  6.             if (Valid_Name.IsMatch(txtName.Text) != true)
  7.             {
  8.                 MessageBox.Show("Namme accepts only alphabetical characters", "Invalid", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
  9.                 txtName.Focus();
  10.                 return;
  11.             }
  12.  
  13.             //for Address 
  14.             if (txtAddress.Text == "")
  15.             {
  16.                 MessageBox.Show("Address cannot be empty!", "Invalid", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
  17.                 txtAddress.Focus();
  18.                 return;
  19.             }
  20.             //for Contacts 
  21.             if (Valid_Contact.IsMatch(txtContactNo.Text) != true)
  22.             {
  23.                 MessageBox.Show("Contact accept numbers only.", "Invalid", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
  24.                 txtContactNo.Focus();
  25.                 return;
  26.             }
  27.             //for username 
  28.             if (txtUsername.Text == "")
  29.             {
  30.                 MessageBox.Show("Username cannot be empty!", "Invalid", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
  31.                 txtUsername.Focus();
  32.                 return;
  33.             }
  34.             //for password 
  35.             if (Valid_Password.IsMatch(txtPassword.Text) != true)
  36.             {
  37.                 MessageBox.Show("Password must be atleast 8 to 15 characters. It contains atleast one Upper case and numbers.", "Invalid", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
  38.                 txtPassword.Focus();
  39.                 return;
  40.             }
  41.             //for Email Address 
  42.             if (Valid_Email.IsMatch(txtEmailAddress.Text) != true)
  43.             {
  44.                 MessageBox.Show("Invalid Email Address!","Invalid",MessageBoxButtons.OK ,MessageBoxIcon.Exclamation );
  45.                 txtEmailAddress.Focus(); 
  46.                 return; 
  47.             }
  48.  
  49.             //success message
  50.           MessageBox.Show("You are now successfully registered.");
  51.  
  52.             //hidding all object in the form
  53.           foreach(Control txt in this.Controls)
  54.           {
  55.               if (txt is Control)
  56.               {
  57.                   txt.Visible = false;
  58.  
  59.               }
  60.           }
  61.  
  62.         }
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