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copied!<p>Please read the <a href="http://cocoawithlove.com/2009/06/verifying-that-string-is-email-address.html" rel="noreferrer">full post</a> over at <a href="http://cocoawithlove.com" rel="noreferrer">http://cocoawithlove.com</a>.</p> <blockquote> <p>In Cocoa, NSPredicate works in much the same way as the "WHERE" clause of SQL. The main reason that NSPredicate is being brought to the iPhone is that NSPredicate fulfils the same role in Core Data that "WHERE" clauses fulfil in SQL — to allow the persistent store to fetch objects that satisfy specific criteria.</p> </blockquote> <pre><code>// given an NSDictionary created used the above method named "row"... NSPredicate *johnSmithPredicate = [NSPredicate predicateWithFormat:@"firstname = 'John' AND lastname = 'Smith'"]; BOOL rowMatchesPredicate = [johnSmithPredicate evaluateWithObject:row]; </code></pre> <p><strong>Verifying an email address</strong></p> <blockquote> <p>The "LIKE" comparison operator in NSPredicate (NSLikePredicateOperatorType) is commonly used as a convenient means of testing if an NSString matches a Regular Expression. It's advantage over full libraries with greater options and replacement capability is that it is already in Cocoa — no libraries, no linkage, no hassle.</p> </blockquote> <p>You can do a simple test: </p> <pre><code>NSPredicate *regExPredicate = [NSPredicate predicateWithFormat:@"SELF MATCHES %@", regularExpressionString]; BOOL myStringMatchesRegEx = [regExPredicate evaluateWithObject:myString]; </code></pre> <blockquote> <p>The only question that remains is: what is a regular expression that can be used to verify that an NSString contains a syntactically valid email address?</p> </blockquote> <pre><code>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])+)\\])"; </code></pre>

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