Strip Non-Alphanumeric Characters from an NSString

We can do this by splitting and then joining. Requires OS X 10.5+ for the componentsSeparatedByCharactersInSet:

NSCharacterSet *charactersToRemove = [[NSCharacterSet alphanumericCharacterSet] invertedSet];
NSString *strippedReplacement = [[someString componentsSeparatedByCharactersInSet:charactersToRemove] componentsJoinedByString:@""];

In Swift, the componentsJoinedByString is replaced by join(...), so here it just replaces non-alphanumeric characters with a space.

let charactersToRemove = NSCharacterSet.alphanumericCharacterSet().invertedSet
let strippedReplacement = " ".join(someString.componentsSeparatedByCharactersInSet(charactersToRemove))

For Swift2 ...

var enteredByUser = field.text .. or whatever

let unsafeChars = NSCharacterSet.alphanumericCharacterSet().invertedSet

enteredByUser = enteredByUser
         .componentsSeparatedByCharactersInSet(unsafeChars)
         .joinWithSeparator("")

If you want to delete just the one character, for example delete all returns...

 enteredByUser = enteredByUser
         .componentsSeparatedByString("\n")
         .joinWithSeparator("")

What I wound up doing was creating an NSCharacterSet and the -invertedSet method that I found (it's a wonder what an extra hour of sleep does for documentation-reading abilities). Here's the code snippet, assuming that someString is the string from which you want to remove non-alphanumeric characters:

NSCharacterSet *charactersToRemove =
[[ NSCharacterSet alphanumericCharacterSet ] invertedSet ];

NSString *trimmedReplacement =
[ someString stringByTrimmingCharactersInSet:charactersToRemove ];

trimmedReplacement will then contain someString's alphanumeric characters.

Swift 3 version of accepted answer:

let unsafeChars = CharacterSet.alphanumerics.inverted
let myStrippedString = myString.components(separatedBy: unsafeChars).joined(separator: "")