This is a conceptual idea: after a sync, show a message bar indicator (for calendars selected beforehand), that X events updates, Y added, Z deleted. Then you can tap on this notification and get a more complete summary where it says “EVENT TITLE updated, EVENT TITLE deleted/added”, etc.
@rfc2822 Thank you very much for the fix. I was going to create an ownCloud issue, but I see you’ve already done so. I’ll copy some of the information from this issue into that so the OC developers can get the information in their own bug report.
Sounds reasonable to me to look e.g. for a “BEGIN: VCALENDAR” and a “BEGIN: EVENT” as well as for a closing “END:VEVENT” and “END:VCALENDAR” as a basic validation. I think from a user perspective this should be fine, the subscription would be fast and as it can happen at any time that a once valid resource becomes invalid (maybe due to an error while the .ics file was created, or a failed file download, or…) I don’t see a drawback in validating the whole file only when synchronizing.