Pro Android with Kotlin

109
CHAPTER 7: Permissions
Acquiring Permissions
The way permissions are handled by the Android OS has changed. Prior to Android 6.0
(API level 23), the permission inquiry asked the user happened during the installation. Starting 
with API level 23, a paradigm change happened: permission inquiry happens during the 
runtime of an app. This made the permission system more flexible; users of your app might 
never use certain parts of it, and thus asking for permission to do so might annoy them.
The downside of this approach is that more programming work is needed. The runtime 
permission inquiry must be included in your code. To do so, at any suitable place before the 
permission is needed, you add the following:
val activity = this
val perm = Manifest.permission.CAMERA
val cameraPermReturnId = 7239 // any suitable constant
val permissionCheck = ContextCompat.checkSelfPermission(
activity, perm)
if (permissionCheck !=
PackageManager.PERMISSION_GRANTED) {
// Should we show an explanation?
if (ActivityCompat.
shouldShowRequestPermissionRationale(
activity, perm)) {
// Show an explanation to the user
// *asynchronously* -- don't block
// this thread waiting for the user's
// response! After the user sees the
// explanation, try again to request
// the permission.
val dialog = AlertDialog.Builder(activity) ...
.create()
dialog.show()
} else {
// No explanation needed, we can request
// the permission.
ActivityCompat.requestPermissions(activity,
arrayOf(perm), cameraPermReturnId)
// cameraPermReturnId is an app-defined
// int constant. The callback method gets
// the result of the request.
}
}
This code does the following:

First we check whether the permission has already been granted. If the 
permission was granted before, the user wouldn’t be asked again unless 
the app got reinstalled or the permission got revoked explicitly.

The ActivityCompat.shouldShowRequestPermissionRationale() method 
checks whether a rationale should be shown to the user. The idea 
behind that is if the user denied the permission inquiry request a couple 
of times, they might have done that because the need for the permission 
was not well understood. In this case, the app gets a chance to tell 

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