Password validation in UITextField in iOS

This is how I would do it. The validation should be done at the end when the user has typed in the password and not in between.I will not be using NSRegularExpression.

-(void)textFieldDidEndEditing:(UITextField *)textField{
   int numberofCharacters = 0;
   BOOL lowerCaseLetter,upperCaseLetter,digit,specialCharacter = 0;
   if([textField.text length] >= 10)
   {
      for (int i = 0; i < [textfield.text length]; i++) 
      {
         unichar c = [textfield.text characterAtIndex:i];
         if(!lowerCaseLetter)
         {
           lowerCaseLetter = [[NSCharacterSet lowercaseLetterCharacterSet] characterIsMember:c];
         }
         if(!upperCaseLetter)
         {
           upperCaseLetter = [[NSCharacterSet uppercaseLetterCharacterSet] characterIsMember:c];
         }
         if(!digit)
         {
            digit = [[NSCharacterSet decimalDigitCharacterSet] characterIsMember:c];
         }
         if(!specialCharacter)
         {
            specialCharacter = [[NSCharacterSet symbolCharacterSet] characterIsMember:c];
         }
      }

      if(specialCharacter && digit && lowerCaseLetter && upperCaseLetter)
      {
         //do what u want
      }
      else
      { 
         UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Error"
                                                        message:@"Please Ensure that you have at least one lower case letter, one upper case letter, one digit and one special character"
                                                       delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
        [alert show];
      }

   }
   else
   {
      UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Error"
                                                        message:@"Please Enter at least 10 password"
                                                       delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
        [alert show];
   }
}

Hope this helps…