Requirements: must contain uppercase letters + lowercase letters + arrays + symbols
NSString * psw = @"Abc123456@!";
NSString * regex1 = @"^[0-9]{8,16}$|^[a-zA-Z]{8,20}$";
NSString * regex2 = @"^[A-Za-z0-9]{8,20}$";
NSString * regex3 = @"^(?=.*\\d)(?=.*[a-z])(?=.*[A-Z]).{8,20}$";
Note: \d in the expression of regular 3 will be regarded as an escape character in iOS, so it needs to be written as \\d, so if you use this regular expression in other languages, remember to remove \
NSPredicate * pred1 = [NSPredicate predicateWithFormat:@"SELF MATCHES %@", regex1];
NSPredicate * pred2 = [NSPredicate predicateWithFormat:@"SELF MATCHES %@", regex2];
NSPredicate * pred3 = [NSPredicate predicateWithFormat:@"SELF MATCHES %@", regex3];
BOOL result1 = [pred1 evaluateWithObject:psw];
BOOL result2 = [pred2 evaluateWithObject:psw];
BOOL result3 = [pred3 evaluateWithObject:psw];
password is true if result1 and result12 fail and result3 passes
if (result1 ==NO && result2 ==NO && result3 ==YES) {
//Password passed, write your logic here
}else{
password failed
}