iOS 判断字母、数字串

以下为NSString的扩展方法，分别是判断字符串是否只是包含字母、是否只包含数字、是否只包含字母和数字：

//只有字母- (BOOL)isOnlyLetters {  NSCharacterSet *letterCharacterset = [[NSCharacterSet letterCharacterSet] invertedSet];  return ([self rangeOfCharacterFromSet:letterCharacterset].location == NSNotFound);}//只有数字- (BOOL)isOnlyNumbers {  NSCharacterSet *numSet = [[NSCharacterSet characterSetWithCharactersInString:@"0123456789"] invertedSet];  return ([self rangeOfCharacterFromSet:numSet].location == NSNotFound);}//字母和数字- (BOOL)isOnlyAlphaNumeric {  NSCharacterSet *numAndLetterCharSet = [[NSCharacterSet alphanumericCharacterSet] invertedSet];  return ([self rangeOfCharacterFromSet:numAndLetterCharSet].location == NSNotFound);}