Check that an email address is valid on iOS

Possible Duplicate:
Best practices for validating email address in Objective-C on iOS 2.0?

I am developing an iPhone application where I need the user to give his email address at login.

What is the best way to check if an email address is a valid email address?

---

Good cocoa function:

-(BOOL) NSStringIsValidEmail:(NSString *)checkString
{
   BOOL stricterFilter = NO; // Discussion http://blog.logichigh.com/2010/09/02/validating-an-e-mail-address/
   NSString *stricterFilterString = @"^[A-Z0-9a-z._%+-]+@([A-Za-z0-9-]+.)+[A-Za-z]{2,4}$";
   NSString *laxString = @"^.+@([A-Za-z0-9-]+.)+[A-Za-z]{2}[A-Za-z]*$";
   NSString *emailRegex = stricterFilter ? stricterFilterString : laxString;
   NSPredicate *emailTest = [NSPredicate predicateWithFormat:@"SELF MATCHES %@", emailRegex];
   return [emailTest evaluateWithObject:checkString];
}

Discussion on Lax vs. Strict - http://blog.logichigh.com/2010/09/02/validating-an-e-mail-address/

And because categories are just better, you could also add an interface:

@interface NSString (emailValidation) 
  - (BOOL)isValidEmail;
@end

Implement

@implementation NSString (emailValidation)
-(BOOL)isValidEmail
{
  BOOL stricterFilter = NO; // Discussion http://blog.logichigh.com/2010/09/02/validating-an-e-mail-address/
  NSString *stricterFilterString = @"^[A-Z0-9a-z._%+-]+@([A-Za-z0-9-]+.)+[A-Za-z]{2,4}$";
  NSString *laxString = @"^.+@([A-Za-z0-9-]+.)+[A-Za-z]{2}[A-Za-z]*$";
  NSString *emailRegex = stricterFilter ? stricterFilterString : laxString;
  NSPredicate *emailTest = [NSPredicate predicateWithFormat:@"SELF MATCHES %@", emailRegex];
  return [emailTest evaluateWithObject:self];
}
@end

And then utilize:

if([@"emailString@email.com" isValidEmail]) { /* True */ }
if([@"InvalidEmail@notreallyemailbecausenosuffix" isValidEmail]) { /* False */ }

---

To check if a string variable contains a valid email address, the easiest way is to test it against a regular expression. There is a good discussion of various regex's and their trade-offs at regular-expressions.info.

Here is a relatively simple one that leans on the side of allowing some invalid addresses through: ^[A-Z0-9._%+-]+@[A-Z0-9.-]+.[AZ]{2,6}$

How you can use regular expressions depends on the version of iOS you are using.

iOS 4.x and Later

You can use NSRegularExpression , which allows you to compile and test against a regular expression directly.

iOS 3.x

Does not include the NSRegularExpression class, but does include NSPredicate , which can match against regular expressions.

NSString *emailRegex = ...;
NSPredicate *emailTest = [NSPredicate predicateWithFormat:@"SELF MATCHES %@", emailRegex];
BOOL isValid = [emailTest evaluateWithObject:checkString];

Read a full article about this approach at cocoawithlove.com.

iOS 2.x

Does not include any regular expression matching in the Cocoa libraries. However, you can easily include RegexKit Lite in your project, which gives you access to the C-level regex APIs included on iOS 2.0.

---

Heres a good one with NSRegularExpression that's working for me.

[text rangeOfString:@"^.+@.+..{2,}$" options:NSRegularExpressionSearch].location != NSNotFound;

You can insert whatever regex you want but I like being able to do it in one line.

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