Flutter - Validate a phone number using Regex

Question

In my futter mobile app, I am trying to validate a phone number using regex. Below are the conditions.

1. Phone numbers must contain 10 digits.

Answer 1

Validation using Regex:

String validateMobile(String value) {
String pattern = r'(^(?:[+0]9)?[0-9]{10,12}$)';
RegExp regExp = new RegExp(pattern);
if (value.length == 0) {
      return 'Please enter mobile number';
}
else if (!regExp.hasMatch(value)) {
      return 'Please enter valid mobile number';
}
return null;
}