Question

This code validates your email field, but I can’t understand how it works.

NSString *e = email.text;
NSString *emailRegEx =@"(?:[a-z0-9!#$%\\&'*+/=?\\^_`{|}~-]+(?:\\.[a-z0-9!#$%\\&'*+/=?\\^_`{|}"
@"~-]+)*|\"(?:[\\x01-\\x08\\x0b\\x0c\\x0e-\\x1f\\x21\\x23-\\x5b\\x5d-\\"
@"x7f]|\\\\[\\x01-\\x09\\x0b\\x0c\\x0e-\\x7f])*\")@(?:(?:[a-z0-9](?:[a-"
@"z0-9-]*[a-z0-9])?\\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?|\\[(?:(?:25[0-5"
@"]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-"
@"9][0-9]?|[a-z0-9-]*[a-z0-9]:(?:[\\x01-\\x08\\x0b\\x0c\\x0e-\\x1f\\x21"
@"-\\x5a\\x53-\\x7f]|\\\\[\\x01-\\x09\\x0b\\x0c\\x0e-\\x7f])+)\\])";

NSPredicate *regExPredicate =[NSPredicate predicateWithFormat:@"SELF MATCHES %@", emailRegEx];
BOOL myStringMatchesRegEx = [regExPredicate evaluateWithObject:e];
NSLog(@"myStringMatchesRegEx = %d ",myStringMatchesRegEx);

Answer 1

thats one huge regular expression 🙂

Basically, the NSPredicate states that it wants to match itself (which is an NSString in the end) with a regular expression (are you familiar with Regular Expressions?) and returns a YES/NO response if the given NSString (which is the email.text) matches that regular expression.

In essence, its making sure that the email text is valid according to the massive regular expression (which I will not go into as it would take hours to get my head around).