Marshmallow brought runtime permissions to the Android world, and by now most apps have started requesting their permissions at runtime instead of install time (you have, right?).
Permissions are grouped into buckets like "location" or "storage" to simplify the explanation of what a permission does for users. Hopefully this is all old news to you.
However there is an interesting situation that merits a little more explanation.
Let's say your app currently requests
ACCESS_COARSE_LOCATION. Your requirements
have changed a little bit, and you now need
ACCESS_FINE_LOCATION. What happens might
not be quite what you expect.
The documentation provides this note:
Note: Your app still needs to explicitly request every permission it needs, even if the user has already granted another permission in the same group.
So we know we need to request the new fine location permission. But what does the user see?
If a user hasn't accepted the coarse location permission (and hasn't said "don't ask again"), your app behaves as you would expect it to on a fresh install. You can request the permission as usual and go on about your day.
If your user has denied the coarse location permission and selected the "never ask again" option, you will not be allowed to ask for either permission. This is also generally what I would expect- the user clearly doesn't want you using their location, so you don't get the opportunity to ask again.
Here's where it gets a little more interesting.
checkSelfPermission()you'll still get
requestPermissions(), you will automatically get a callback to
onRequestPermissionsResult()with the fine location permission granted. This is transparent to your user- they will not see a dialog.
If your app already requests a permission in a particular permission group, you still need to explicitly request all other permissions in that group that you want to use. However, if your user has already accepted one of the other permissions in that group, they will not see another permission request dialog.