All my contacts/events are gone after I reboot my phone.
(This problem only affects users of some Android 4.1 devices and some Samsung devices, regardless of which Android version they have installed).
When booting, Android checks if there are orphaned contacts which are not associated to a sync adapter. Unfortunately, this check is sometimes run before decrypting paid apps from Play store. So, Android doesn't find the sync adapter, thinks that all your entries are orphaned and deletes them.
Is DAVdroid compatible with Android below version 4?
No. Its build on technology that has been introduced with Android 4.0 (Ice Cream Sandwich), namely Calendar/Contact Contracts.
Is there any difference in functionality between DAVdroid in the Samsung/Play Store and the free version?
Why do you ask for donations when I have paid for the app anyway?
We decided to make it possible to get the app for free via the F-Droid market. If you download the app there, we encourage you to think about a donation of your choice, because making the app was much work. But of course, DAVdroid is free and open-source and you don't have to pay for it.
I always get the error message "I/O error: No peer certificate" or "Cannot verify hostname" when accessing my server that uses a self-signed certificate.
Your Android device couldn't verify the certificate. Host name and certificate verification are very important security features – it means that if somebody else generates another self-signed certificate for your host name and tricks you into using it (e.g. by DNS manipulation), DAVdroid will reject this wrong certificate and won't transmit private data to the attacker.
If you're not a victim of a man-in-the-middle attack and this message appears, you might have to import your certificate (or the certficate of your CA) into the Android credentials storage. For details, please see Using a self-signed certificate with Android.
Does DAVdroid support Server Name Indication (SNI)?
DAVdroid 0.4+ supports SNI on Android 4.2+ devices. For older Android versions and when updating [to stock or Cynogen firmware] is no option, I recommend to mount your DAV service into the main HTTPS virtual host so that there's no need for SNI. You may also use IP- or port-based virtual SSL hosts.
How can I change the URL/user name/password of my DAV resource or add a new calendar?
At the moment, there's no other way than to delete your DAVdroid account from your device and then add it again.
I have added my address book and calendar(s) and they're shown correctly, but no entries are synchronized.
Make sure that Cyanogen Privacy Guard doesn't prevent DAVdroid access to the address book/calendars.
My device shows only one input field per postal address. How can I enter a structured address (with street, postal code, locality, etc.)?
This is not related to DAVdroid but is an issue of your contact editor. The default contact editor behaves like this: If a structured address is known (for instance, because DAVdroid downloaded it from your server), the formatted address will be shown (as expected). However, if this single field is empty and you enter something into it, it will be stored as "street". See this ICS People app bug report.
We have tested DAVdroids functionality with various platforms, providers and servers.
DAVdroid is designed to be an open-source project from the very first beginning. It is always possible to compile the app yourself and use it for free without any obligations. The source code is available on Github, and you can download the app on F-Droid.
However, it was much work to create this app, so we have decided to put it into the Google Play Store for a small fee. If you want to support this project, please consider donating to DAVdroid or purchasing it via Google Play.