If you are using the provided CrudManager, then https://www.bryntum.com/docs/calendar/api/Calendar/feature/LoadOnDemand would be the way to go.
If you are doing this yourself, listen for this event: https://www.bryntum.com/docs/calendar/api/Calendar/view/Calendar#event-dateRangeChange
currently I am assigning events, resources and assignments after getting data from API. If that is the case, I believe in this case I can write an event to load api data with CrudManager, and then form the resources, events and assignments.
Can I still use crud manager and get the data outside the CrudManager?