[c#] Phone Number Validation MVC

I am trying to use a regular expression to validate a phone number and return an error when an invalid number or phone number is submitted.

MVC Code:

<ol class="row">
    <li class="cell" style="width: 20%;">Phone Number:</li>
    <li class="cell last" style="width: 60%;">
        @Html.TextBoxFor(model => model.PhoneNumber, new { @class = "textbox" }) 
        @Html.ValidationMessageFor(model => model.PhoneNumber)
    </li>
</ol>

C# Code:

[DataType(DataType.PhoneNumber)]
[Display(Name = "Phone Number")]
[Required(ErrorMessage = "Phone Number Required!")]
[RegularExpression(@"^\(?([0-9]{3})\)?[-. ]?([0-9]{3})[-. ]?([0-9]{4})$",
                   ErrorMessage = "Entered phone format is not valid.")]
public string PhoneNumber { get; set; }

However, the input box will not show a message to the user indicating that the phone number which was submitted is not valid.

Along with the above answers Try this for min and max length:

In Model

[StringLength(13, MinimumLength=10)]
public string MobileNo { get; set; }

In view

 <div class="col-md-8">
           @Html.TextBoxFor(m => m.MobileNo, new { @class = "form-control" , type="phone"})
           @Html.ValidationMessageFor(m => m.MobileNo,"Invalid Number")
           @Html.CheckBoxFor(m => m.IsAgreeTerms, new {@checked="checked",style="display:none" })
  </div>

[DataType(DataType.PhoneNumber)] does not come with any validation logic out of the box.

According to the docs:

When you apply the DataTypeAttribute attribute to a data field you must do the following:

• Issue validation errors as appropriate.

The [Phone] Attribute inherits from [DataType] and was introduced in .NET Framework 4.5+ and is in .NET Core which does provide it's own flavor of validation logic. So you can use like this:

[Phone()]
public string PhoneNumber { get; set; }

However, the out-of-the-box validation for Phone numbers is pretty permissive, so you might find yourself wanting to inherit from DataType and implement your own IsValid method or, as others have suggested here, use a regular expression & RegexValidator to constrain input.

Note: Use caution with Regex against unconstrained input per the best practices as .NET has made the pivot away from regular expressions in their own internal validation logic for phone numbers

Try this:

[DataType(DataType.PhoneNumber, ErrorMessage = "Provided phone number not valid")]

Try for simple regular expression for Mobile No

[Required (ErrorMessage="Required")]
[RegularExpression(@"^(\d{10})$", ErrorMessage = "Wrong mobile")]
public string Mobile { get; set; }

You don't have a validator on the page. Add something like this to show the validation message.

@Html.ValidationMessageFor(model => model.PhoneNumber, "", new { @class = "text-danger" })

The phone number data annotation attribute is for the data type, which is not related to the data display format. It's just a misunderstanding. Phone number means you can accept numbers and symbols used for phone numbers for this locale, but is not checking the format, length, range, or else. For display string format use the javascript to have a more dynamic user interaction, or a plugin for MVC mask, or just use a display format string properly.

If you are new to MVC programming put this code at the very end of your view file (.cshtml) and see the magic:

<script src="https://code.jquery.com/jquery-3.5.1.min.js" integrity="sha256-9/aliU8dGd2tb6OSsuzixeV4y/faTqgFtohetphbbj0=" crossorigin="anonymous"></script>
<script type="text/javascript">
    $(document).ready(function () {
        $("#the_id_of_your_field_control").keyup(function () {
            $(this).val($(this).val().replace(/^(\d{2})(\d{5})(\d{4})+$/, "($1) $2-$3"));
        });
    });
</script>

This format is currently used for mobile phones in Brazil. Adapt for your standard.

This will add the parenthesis and spaces to your field, which will increase the string length of your input data. If you want to save just the numbers you will have to trim out the non-numbers from the string before saving.

To display a phone number with (###) ###-#### format, you can create a new HtmlHelper.

Usage

@Html.DisplayForPhone(item.Phone)

HtmlHelper Extension

public static class HtmlHelperExtensions
{
    public static HtmlString DisplayForPhone(this HtmlHelper helper, string phone)
    {
        if (phone == null)
        {
            return new HtmlString(string.Empty);
        }
        string formatted = phone;
        if (phone.Length == 10)
        {
            formatted = $"({phone.Substring(0,3)}) {phone.Substring(3,3)}-{phone.Substring(6,4)}";
        }
        else if (phone.Length == 7)
        {
            formatted = $"{phone.Substring(0,3)}-{phone.Substring(3,4)}";
        }
        string s = $"<a href='tel:{phone}'>{formatted}</a>";
        return new HtmlString(s);
    }
}

Or you can use JQuery - just add your input field to the class "phone" and put this in your script section:

$(".phone").keyup(function () {
        $(this).val($(this).val().replace(/^(\d{3})(\d{3})(\d)+$/, "($1)$2-$3"));

There is no error message but you can see that the phone number is not correctly formatted until you have entered all ten digits.