Tim Hunt

Another option is this:

If you are able to edit the qusetion, to change which answer is graded right, then you can do that, then go to Results -> Grades, and regrade all attempts, and the scores will be updated. (However, that does not have the same effect as setting the mark for the question to 0.)

Since Andrew did not link it in his post: https://www.php-fig.org/psr/psr-11/

If you basically want all the features of mod quiz, with just one added feature: teacher controls when students can attempt each question in a classroom situation, I am wondering if creating a whole activitity which duplciates all the quiz funcitonality is the best approach.

I am wondering if you could build this by making a sub-plugin for the quiz. Sepecifically, could you do this using a Quiz access rule plugin? I don't know if that is acutally possible, since the quiz access rule system was not designed for this. However, people have done many creative things using Quiz access rules, which were not orgininally intended, so by creating (ab)use of the API, it might be possible.

https://docs.moodle.org/dev/Quiz_access_rules

Very hard to work ou why this is happening without more information. I wish that error message would tell us what string is being passed where in int is expected.

For what it is worth, the error is coming from this line: https://github.com/moodle/moodle/blob/MOODLE_401_STABLE/mod/quiz/classes/structure.php#L699. So, a few lines above, $this->get_slot_by_number($slotnumber) must have returned something where questionid is not an id.

Are you sure you are on 4.1.6+? Your symptoms seem a lot like MDL-74452, which was fixed in 4.1.3.

Note, if the contents of a file reference is two different places are identical, then Moodle will only ever store one copy of that file.

Are you sure this is an issue?