Allow only alphanumeric characters for a UITextField

Question

How would I go about allowing inputting only alphanumeric characters in an iOS UITextField?

Answer 1

Use the UITextFieldDelegate method -textField:shouldChangeCharactersInRange:replacementString: with an NSCharacterSet containing the inverse of the characters you want to allow. For example:

// in -init, -initWithNibName:bundle:, or similar NSCharacterSet *blockedCharacters = [[[NSCharacterSet alphanumericCharacterSet] invertedSet] retain];  - (BOOL)textField:(UITextField *)field shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)characters {     return ([characters rangeOfCharacterFromSet:blockedCharacters].location == NSNotFound); }  // in -dealloc [blockedCharacters release]; 

Note that you’ll need to declare that your class implements the protocol (i.e. @interface MyClass : SomeSuperclass <UITextFieldDelegate>) and set the text field’s delegate to the instance of your class.

Answer 2

Swift 3 version

Currently accepted answer approach:

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {      // Get invalid characters     let invalidChars = NSCharacterSet.alphanumerics.inverted      // Attempt to find the range of invalid characters in the input string. This returns an optional.     let range = string.rangeOfCharacter(from: invalidChars)      if range != nil {         // We have found an invalid character, don't allow the change         return false     } else {         // No invalid character, allow the change         return true     } } 

Another equally functional approach:

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {      // Get invalid characters     let invalidChars = NSCharacterSet.alphanumerics.inverted      // Make new string with invalid characters trimmed     let newString = string.trimmingCharacters(in: invalidChars)      if newString.characters.count < string.characters.count {         // If there are less characters than we started with after trimming         // this means there was an invalid character in the input.          // Don't let the change go through         return false     } else {         // Otherwise let the change go through         return true     }  }