Provide workaround for incomplete Android EXDATE support

[rfc2822]

See http://stackoverflow.com/questions/14522393/android-exdate-format-when-adding-a-calendar-event

Android has a very own implementation of the EXDATE property which causes that 1:1 synchronization of iCal events with EXDATE Android calendar provider EXDATE doesn’t work.

DAVdroid could (should?) rewrite .ical EXDATEs so that they are understood by the Android calendar provider.

[AutoImport-LudovicRousseau]

I can reproduce the problem using my DAViCal server. The problem is also present when using AndroidCaldavSyncAdapater https://github.com/gggard/AndroidCaldavSyncAdapater. It is not surprising if it is a bug in Android and not in the sync adapter themselves.

[AutoImport-rvandegrift]

More info for this problem: DAVDroid 0.5.2 on my phone (Android 4.0) and tablet (Android 4.3) against a DAViCal server. Modifying an instance of a repeating even works correctly on the device used to modify it, but the change is not properly synced. Steps:

1. On phone: reschedule one instance of a repeating event to a different time. (works as expected)
2. Wait for/trigger syncs.
3. On tablet: The original repeating event appears, and a new individual event at the rescheduled time.
4. Thunderbird and CalDavZap see the same thing: original instance, plus a new event at the new time.

If I delete the rescheduled instance using CalDavZAP, then DAVDroid:

• on the tablet: syncs the delete as expected
• on the phone: goes haywire, crashing on every sync

[rfc2822]

As this is not a DAVdroid problem and there are far more important issues, I’ll close this for now.

[AutoImport-jondo]

Reading the corresponding kolab feature request, I wonder whether a workaround is even possible.

[AutoImport-jondo]

This unanswered Stackoverflow question sounds related.

Also, these two issues point to the Google Product Forums. The only forum that sounded somehow suitable was the one for Nexus devices, so I posted the problem there.

[rfc2822]

Note: should be implemented with 5b7947034a656c463ca477e198f7728cccc9e4c1

[AutoImport-jondo]

I have now testing DAVdroid 0.8.3 against Kolab (kolabnow.com) again, and I am generally happy:

• When I delete an instance of a recurring event series on the phone, the instance stays visible in the Kolab web interface, but becomes striked through and gets the annotation “cancelled”, with the option to fully delete it on the kolab server.
  I’d have expected the instance to be fully deleted automatically, but I can live with the situation.
• When I delete an instance of a recurring event series in the Kolab web interface or mark it as cancelled, the instance is deleted on the phone.
  This is also fine for me. I assume the status “cancelled” cannot be represented on the phone.

So: Thank you!