RegularExpressionValidator In ASP.NET

Introduction

Here, I show you the use of RegularExpressionValidator to validate various expressions like:

1. EmailID
2. U.S. Phone Number

Background

It is a common requirement for beginners in ASP.NET to write various validation expressions when creating a form to register a user.

It is necessary to specify that RegularExpressionValidator is validating which control. In the ControlToValidate property, we specify the control which will be validated. For this, we need to mention the ID of the textbox control.

RegularExpressionValidator for Email ID

Here, I have shown a textbox with ID="txtEmail".

  <asp:TextBox ID="txtEmail" runat="server"></asp:TextBox>
                <asp:RequiredFieldValidator ID="rfvEmail" runat="server" 
                ErrorMessage="*" ControlToValidate="txtEmail"
                    ValidationGroup="vgSubmit" ForeColor="Red"></asp:RequiredFieldValidator>
                <asp:RegularExpressionValidator ID="RegularExpressionValidator2" 
                runat="server" ErrorMessage="Please Enter Valid Email ID"
                    ValidationGroup="vgSubmit" ControlToValidate="txtEmail" 
                    CssClass="requiredFieldValidateStyle"
                    ForeColor="Red" 
                    ValidationExpression="\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*">
                    </asp:RegularExpressionValidator>

RegularExpressionValidator for U.S. Phone Number

 <asp:TextBox ID="txtPhoneNumber" runat="
server"></asp:TextBox>(000-000-0000)
                <asp:RequiredFieldValidator ID="rfvPhoneNumber" runat="server" 
                ErrorMessage="*" ControlToValidate="txtPhoneNumber"
                    ValidationGroup="vgSubmit" ForeColor="Red"></asp:RequiredFieldValidator>
                <asp:RegularExpressionValidator ID="RegularExpressionValidator1" 
                runat="server" ErrorMessage="Phone Number is not valid"
                    ValidationGroup="vgSubmit" ControlToValidate="
                    txtPhoneNumber" ForeColor="Red"
                    ValidationExpression="((\(\d{3}\) ?)|(\d{3}-))?\d{3}-\d{4}">
                    </asp:RegularExpressionValidator>

Points of Interest

These are the most common validation expressions used to validate an Email ID and phone number.

There is no way to check the false Email IDs. They can be checked by the mail servers only.

There is no way to check the false phone numbers. They are also checked by the Phone agencies.

These regular expressions only check the expression pattern for an email or a phone number.