Pro Android with Kotlin

110
CHAPTER 7: Permissions
the user more about the permission need. The frequency of how often 
shouldShowRequestPermissionRationale() returns true is up to the 
Android OS. The example here shows a dialogue; you can of course do 
whatever you want here to inform the user.
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The ActivityCompat.requestPermissions(...) method finally performs 
the permission inquiry. This happens asynchronously, so the call returns 
immediately.
Once the call to ActivityCompat.requestPermissions(...) happens, the user gets asked by 
the Android OS, outside your app, whether they want to grant the permission. The result of 
that will show up in an asynchronous callback method as follows:
override
fun onRequestPermissionsResult(
requestCode: Int, permissions: Array,
grantResults: IntArray) {
when (requestCode) {
cameraPermReturnId -> {
// If request is canceled, the result
// arrays are empty. Here we know it just
// can be one entry
if ((grantResults.isNotEmpty()
&& grantResults[0] ==
PackageManager.PERMISSION_GRANTED)) {
// permission was granted
// act accordingly...
} else {
// permission denied
// act accordingly...
}
return
}
// Add other 'when' lines to check for other
// permissions this App might request.
else -> {
// Ignore all other requests.
// Or whatever makes sense to you.
}
}
}
This method needs to be implemented inside an android.content.Activity class. In other 
contexts, this is not possible.
Acquiring Special Permissions
Using ActivityCompat.requestPermissions() in certain circumstances is not enough to 
acquire permissions SYSTEM_ALERT_WINDOW and WRITE_SETTINGS. For those two permissions, 
you need to follow a different approach.
The permission WRITE_SETTINGS for API levels 23 and higher must be acquired using a 
special intent as follows:

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