How to check if a string only contains alphanumeric characters in objective C?

If you don’t want to bring in a regex library for this one task…

NSString *str = @"aA09";
NSCharacterSet *alphaSet = [NSCharacterSet alphanumericCharacterSet];
BOOL valid = [[str stringByTrimmingCharactersInSet:alphaSet] isEqualToString:@""];