Develop Reference

How do I create a single permission check in my android app?

I am programming an app that connects to a device via Bluetooth, but every time I want to do something with the BluetoothDevice I have to insert a permission check like this (Kotlin):
if (ActivityCompat.checkSelfPermission(this, Manifest.permission.BLUETOOTH_CONNECT) != PackageManager.PERMISSION_GRANTED) {
ActivityCompat.requestPermissions(
this,
arrayOf(Manifest.permission.BLUETOOTH_CONNECT),
42
)
}
Is there a workaround with one single permission check in the beginning of the app?
Thank you!

We have to check permission granted, otherwise it may crash your app.
but we can do in very handy way in Kotlin.
Follow below steps...
In your MainActivity or Very first activity, ask Bluetooth permission like below.
Create Permission Callback in Activity.
private val requestPermissionsLauncher = registerForActivityResult(ActivityResultContracts.RequestMultiplePermissions()) { permissions ->
if (permissions.all { it.value }) Toast.makeText(
this,
"Permission Granted",
Toast.LENGTH_SHORT
).show()
else Toast.makeText(this, "not accepted all the permissions", Toast.LENGTH_LONG).show()
}
Request a permission in onCreate method of Activity.
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
//your code
requestPermissionsLauncher.launch(
arrayOf(android.Manifest.permission.BLUETOOTH_CONNECT)
) //asking permission whatever we need to run app.
}
Create a kotlin Extension function to make sure to run only on Bluetooth permission is Granted.
fun <T> Context.runOnBluetoothPermission(block: () -> T) {
if (ActivityCompat.checkSelfPermission(this, Manifest.permission.BLUETOOTH_CONNECT) == PackageManager.PERMISSION_GRANTED) {
block()
} else {
Toast.makeText(
this,
"Bluetooth permission need to work this.",
Toast.LENGTH_SHORT
).show()
}
}
Use it extension function wherever you need.
example :
In SecondActivity.kt
class SecondActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
//ui functions
//apicalls if any
//functions that only run on Bluetooth permission
runOnBluetoothPermission{
getAllBluetoothDevices()
}
}
private fun getAllBluetoothDevices(){
//your code to get all bluetooth devices.
}
}

The user can revoke the permission at any time, by going to the app settings. When the permission is revoked, the activity will be recreated. This means you have to check at least once after onCreate and before using the permission, if you still have the permission.
TL;DR
No, your app might crash.

Unable to read internal storage in Android Kotlin

I come to you in a time of great need. I am currently learning to use Kotlin for app development and as a "project" per-say, I am working on a simple "File manager". The current problem I am experiencing is that I am unable to read the directories and the files.
Using API 26
Using Kotlin
Using ViewModel
The permissions in the AndroidManifest.xml are set
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
The permission request in runtime is called in MainActivity
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
if (checkPermission()) {
//permission allowed
val path = Environment.getExternalStorageDirectory().path
val filesAndFolders: Array<File>? = File(path).listFiles()
Log.d("FILETAG", path) // /storage/emulated/0
Log.d("FILETAG", filesAndFolders.toString()) // null
Log.d("FILETAG", File(path).exists().toString()) // true
Log.d("FILETAG", File(path).canRead().toString()) // false
} else {
//permission not allowed
requestPermission()
}
if (savedInstanceState == null) {
supportFragmentManager.beginTransaction()
.replace(R.id.container, MainFragment.newInstance())
.commitNow()
}
}
}
private fun checkPermission(): Boolean {
val result =
ContextCompat.checkSelfPermission(
this,
android.Manifest.permission.READ_EXTERNAL_STORAGE
)
return result == PackageManager.PERMISSION_GRANTED
}
private fun requestPermission(){
if(ActivityCompat.shouldShowRequestPermissionRationale(this, android.Manifest.permission.READ_EXTERNAL_STORAGE)){
Toast.makeText(this, "Storage permission is required", Toast.LENGTH_SHORT).show()
} else {
ActivityCompat.requestPermissions(
this,
arrayOf(Manifest.permission.READ_EXTERNAL_STORAGE),
111
)
}
}
As commented in the code, the file array is returned as a "null", though the files seem to exist but are unreadable.
Additionally, I have tried executing this code from an inside of the fragment, but with the exact same results, though am required to read the files in a fragment rather than inside the MainActivity (But I first need to get this part of my code working before I move on to the fragments) and list the files in a RecyclerView.
This is my first question on Stackoverflow, if I missed any essential detail, let me know.
Please grant me your infinite knowledge, thank you.

How to detect permission's permanent deny in Android 11?

In Android 11, when user select "deny" option for more than once for any permission request, then system will mark it as "Permanently denied".Once permanently denied, user has to enable in settings.From this time shouldShowRequestPermissionRationale() start's to return false
Three options are available for permission window , "Deny","Allow All time","Allow only this time". But in settings "Deny","Allow all the time","Ask every time" are present.
How to find when user selects "Ask me every time" from settings, because, checkSelfPermission() returns PackageManager.PERMISSION_DENIED,and shouldShowRequestPermissionRationale() return false. In this time I want to show permission window, instead of move to settings. Something similar to google map permission

Using the new ActivityResultsContract you can do this in the following manner
private val requestPermissionLauncher =
registerForActivityResult(
ActivityResultContracts.RequestMultiplePermissions()
) { result: MutableMap<String, Boolean> ->
val deniedList: List<String> = result.filter {
!it.value
}.map {
it.key
}
when {
deniedList.isNotEmpty() -> {
val map = deniedList.groupBy { permission ->
if (shouldShowRequestPermissionRationale(permission)) DENIED else EXPLAINED
}
map[DENIED]?.let {
// request denied , request again
}
map[EXPLAINED]?.let {
//request denied ,send to settings
}
}
else -> {
//All request are permitted
}
}
}
In OnCreate()[Make sure you ask permission in OnCreate , else application will crash] , ask the permission :
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
requestPermissionLauncher.launch(REQUIRED_PERMISSIONS)
}
Ask requiredPermissions in the following manner :
private val REQUIRED_PERMISSIONS = arrayOf(
Manifest.permission.CAMERA,
Manifest.permission.READ_EXTERNAL_STORAGE
)

Actually there is one more scenario:
if the user let you request the permission but don't chose any option and dismissed the dialog by tapping outside, the request finishes with denied and shouldShowRequestPermissionRationale() returns false.
That is the exact same behaviour as if the user selects don't ask again.
the permission where requested once, it results in denied and we should not show a explanation.
therefore we have to track if shouldShowRequestPermissionRationale() has returned true for once. if it switches back to false its denied permanent.

Use the following method in your activity (Camera permission is used in this example):
private fun requestPermission() {
if (ContextCompat.checkSelfPermission(this, Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
if (ActivityCompat.shouldShowRequestPermissionRationale(this, Manifest.permission.CAMERA)) {
//Permission is denied
} else {
//ask permission
ActivityCompat.requestPermissions(this, arrayOf(Manifest.permission.CAMERA), REQUEST_CODE_CAMERA)
}
}
}

You only need to check the shouldShowRequestPermissionRationale() after user deny the permission
val requestPermissionLauncher = registerForActivityResult(
ActivityResultContracts.RequestPermission()
) { isGranted: Boolean ->
if (isGranted) {
} else {
if(shouldShowRequestPermissionRationale(Manifest.permission.YOUR_RUNTIME_PERMISSION)){
//user hasn't denied permission permanently
}else{
//user has denied permanently,
//you should try to redirect user to settings
//to ask user grant it manually
}
}
}
requestPermissionLauncher.launch(Manifest.permission.YOUR_RUNTIME_PERMISSION)

I am making a gallery like UI for my app, what permissions do i need to ask for if I am targetting Android 11?

I am using MediaStore to recieve the ids of all the images stored on the device using
private fun getImageUris(): List<Uri> {
val uri = MediaStore.Images.Media.EXTERNAL_CONTENT_URI
val projection = arrayOf(MediaStore.Images.Media._ID)
val mCursor = requireActivity().contentResolver.query(
uri,
projection,
null,
null,
null
)
val imageUris = mutableListOf<Uri>()
while (mCursor?.moveToNext() == true) {
val columnIndex = mCursor.getColumnIndex(MediaStore.Images.Media._ID)
val imageId = mCursor.getInt(columnIndex)
val currentImageUri = Uri.withAppendedPath(uri, imageId.toString())
imageUris.add(currentImageUri)
}
mCursor?.close()
return imageUris
}
and then i ask for the permission in onViewCreated() of my fragment like this:
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
binding = FragmentMainBinding.bind(view)
when {
isStoragePermissionGranted -> {
binding.recyclerView.adapter = RecyclerViewAdapter(getImageUris())
}
shouldShowRequestPermissionRationale -> {
Toast.makeText(mainActivity, "Please grant storage permission", Toast.LENGTH_SHORT).show()
requestPermissions(arrayOf(Manifest.permission.READ_EXTERNAL_STORAGE), STORAGE_PERMISSION_REQUEST_CODE)
}
else -> {
Toast.makeText(mainActivity, "Permission not granted. Images cannot be shown.", Toast.LENGTH_SHORT).show()
}
}
}
I expect this to ask for the storage permission as soon as the app is opened (and my fragment is created) and then it should load all the images on the phone in my recycler view (I am using glide). But it doesn't work the way its expected to, instead the
"Permission not granted. Images cannot be shown."
toast message is shown

For a quick workaround, you can add this in the manifest file under <application>
android:requestLegacyExternalStorage="true"
Read about the storage update for Android 11 here

The problem was here as noted by #blackapps
shouldShowRequestPermissionRationale -> {
Toast.makeText(mainActivity, "Please grant storage permission", Toast.LENGTH_SHORT).show()
requestPermissions(arrayOf(Manifest.permission.READ_EXTERNAL_STORAGE), STORAGE_PERMISSION_REQUEST_CODE)
because shouldShowRequestPermissionRationale is only true when the "deny and don't ask again" option is showing with the permission pop up and that option only appears after the first time the permission has been asked for (which never happens since in order for that to happen, shouldShowRequestPermissionRationale needs to be true).

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
use above permission and in application write below code:
<application
android:usesCleartextTraffic="true"
android:requestLegacyExternalStorage="true"/

rxLocationManager looping

I've made a LocationManager to handle permission issues and return lastLocation from FusedLocationProviderClient. It uses RxJava heavily to avoid callback hell. Here's the code:
object LocationManager {
// using coarse location to not ask for GPS enabling
// after changing to ACCESS_FINE_LOCATION don't forget to check GPS settings
private const val LOCATION_PERMISSION = Manifest.permission.ACCESS_COARSE_LOCATION
private var permissionSubject = AsyncSubject.create<Boolean>()
fun loadLastLocation(activity: Activity): Observable<Location?> =
checkPermission(activity).flatMap { hasPermission ->
// check permission, then request last location
Log.d("qwerty", "hasPermission=$hasPermission")
if (hasPermission) requestLastLocation(activity)
else Observable.error<Location>(Exception("Permission not granted"))
}
private fun checkPermission(activity: Activity): Observable<Boolean> =
if (activity.hasPermission(LOCATION_PERMISSION)) Observable.just(true)
else requestPermission(activity)
private fun requestPermission(activity: Activity): Observable<Boolean> = permissionSubject.apply {
// result will be posted to subject later
Log.d("qwerty", "requestPermission $LOCATION_PERMISSION")
ActivityCompat.requestPermissions(activity, arrayOf(LOCATION_PERMISSION), RequestCode.LOCATION_PERMISSION)
}
// call this from hosting activity or you can never get lastLocation
fun onRequestPermissionsResult(requestCode: Int, grantResults: IntArray) {
if (requestCode == RequestCode.LOCATION_PERMISSION) {
permissionSubject.apply {
val granted = grantResults.isNotEmpty() && grantResults[0] == PackageManager.PERMISSION_GRANTED
Log.d("qwerty", "onRequestPermissionsResult=$granted")
onNext(granted)
onComplete()
}
}
// skip other request codes
}
#SuppressLint("MissingPermission")
// check ACCESS_COARSE_LOCATION or ACCESS_FINE_LOCATION before calling this
private fun requestLastLocation(activity: Activity): Observable<Location?> = PublishSubject.create<Location>().apply {
Log.d("qwerty", "requestLastLocation")
LocationServices.getFusedLocationProviderClient(activity).lastLocation
.addOnSuccessListener { location ->
Log.d("qwerty", "lastLocation=$location")
onNext(location)
onComplete()
}
.addOnFailureListener { error ->
Log.d("qwerty", "lastLocation error: ${error.message}")
onError(error)
}
}
}
And fragment calls LocationManager like this:
LocationManager.loadLastLocation(activity!!)
.subscribe(
{ location -> Log.d("qwerty", "fragment got location $location")},
{ error -> error.printStackTrace() }
)
The problem is Observable stucks in infinite loop trying to get permission. Here's what I get in logs, infinite times:
qwerty: requestPermission android.permission.ACCESS_COARSE_LOCATION
qwerty: hasPermission=false
System.err: java.lang.Exception: Permission not granted...
qwerty: onRequestPermissionsResult=false
Can someone tell me what's wrong with this code?

as far as I can see from this code, it should work properly. Please check in your manifest that it tag contain the same permission that you are requesting. And second one, please check in you Location manager imports, that proper Manifest class is imported (android.Manifest not your.app.package.Manifest).