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Unable to scan or discover BT and BLE devices in android

I am a complete novice in Java and Android. I am trying to create a test app to listen for BLE and BT devices nearby. I have another device where I wrote some logic to broadcast its BLE beacons. I verified it using a playstore app. Now I am trying to write my own app on Android.
I have been reading the Android developer pages for guidance. I have literally followed every step of the following pages
https://developer.android.com/guide/topics/connectivity/bluetooth/setup
https://developer.android.com/guide/topics/connectivity/bluetooth/permissions
https://developer.android.com/guide/topics/connectivity/bluetooth/find-bluetooth-devices
https://developer.android.com/guide/topics/connectivity/bluetooth/find-ble-devices
Also, Note that I have used BARE MINIMUM CODE from the Android Developers page So here is what I have done.
1. First off I have added my permissions under AndroidManifest
Note1 : I am deploying this app to My phone running Android 11
Note2 : All this code is written inside MainActivity. I have not created any other activity class
<uses-permission android:name="android.permission.BLUETOOTH" android:maxSdkVersion="30" />
<uses-permission android:name="android.permission.BLUETOOTH_ADMIN" android:maxSdkVersion="30" />
<uses-permission android:name="android.permission.BLUETOOTH_SCAN" />
<uses-permission android:name="android.permission.BLUETOOTH_ADVERTISE" />
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
<uses-permission android:name="android.permission.BLUETOOTH_CONNECT" />
2. Next I check if my BT is enabled.
if (bluetoothAdapter == null) {
blefinder.append("\nDEVICE DOES NOT SUPPORT BLUETOOTH");
}
else {
blefinder.append("\nDEVICE SUPPORTS BLUETOOTH");
}
I get the success message that BT is of course enabled
3. Next I check if my device supports BLE
if (!getPackageManager().hasSystemFeature(PackageManager.FEATURE_BLUETOOTH_LE)) {
blefinder.append("\nBLE NOT SUPPORTED ON THIS DEVICE : ");
finish();
}
else{
blefinder.append("\nBLE IS SUPPORTED ON THIS DEVICE : ");
}
I get the message that BLE is supported
4. Next I list my already paired/bonded devices
For this I call ListPairedAndBondedDevices(); in onCreate() itself right after the above steps. Function Definition Below.
private void ListPairedAndBondedDevices(){
#SuppressLint("MissingPermission") Set<BluetoothDevice> pairedDevices = bluetoothAdapter.getBondedDevices();
if (pairedDevices.size() > 0) {
// There are paired devices. Get the name and address of each paired device.
blefinder.append("\nPAIRED/BONDED DEVICES");
for (BluetoothDevice device : pairedDevices) {
blefinder.append("\n" + device.getName() + " | " + device.getAddress());
}
}
}
This also works like a charm and prints out my paired devices. The next 2 parts is where I face the problem.
5. The Problem Step | Part 1:
Here I register a Broadcast receiver to discover all BT devices in the vicinity. I've unbonded my BT headphones and kept it in pairing mode to verify this.
ListPairedAndBondedDevices(); // From previous code snippet
IntentFilter filter = new IntentFilter(BluetoothDevice.ACTION_FOUND); // New code statement
registerReceiver(BTReceiver, filter);// New code statement
Broadcast Receiver implementation
private final BroadcastReceiver BTReceiver = new BroadcastReceiver() {
#SuppressLint("MissingPermission")
public void onReceive(Context context, Intent intent) {
String action = intent.getAction();
if (BluetoothDevice.ACTION_FOUND.equals(action)) {
// Discovery has found a device. Get the BluetoothDevice
// object and its info from the Intent.
BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
blefinder.append("\n" + device.getName() + " | " + device.getAddress());
}
}
};
So This part didn't Work :(
If you see above, I am registering the BTReceiver in onCreate right after listing the already paired devices (by calling ListPairedAndBondedDevices()).
When I ran the debugger, this broadcast receiver never gets called.
6. The Problem Step | Part 2:
Right after this I try to scan for BLE Devices as well by callin scanLeDevice()
ListPairedAndBondedDevices(); // From previous snippet
IntentFilter filter = new IntentFilter(BluetoothDevice.ACTION_FOUND); // From previous snippet
registerReceiver(BTReceiver, filter);// From previous snippet
scanLeDevice(); // ---------------->>> CALLING THIS FUNCTION TO SCAN FOR BLE DEVICES
Implementation of scanLeDevice()
private void scanLeDevice() {
if (!scanning) {
// Stops scanning after a predefined scan period.
handler.postDelayed(new Runnable() {
#Override
public void run() {
scanning = false;
bluetoothLeScanner.stopScan(leScanCallback);
blefinder.append("\nSTOPPING BLE SCAN... TIMEOUT REACHED");
}
}, SCAN_PERIOD);
scanning = true;
bluetoothLeScanner.startScan(leScanCallback);
} else {
scanning = false;
bluetoothLeScanner.stopScan(leScanCallback);
blefinder.append("\nSTOPPING BLE SCAN");
}
}
Unfortunately this also fails. The debugger tells me that this part of the code is getting called.
And after 30 seconds of SCAN_PERIOD (The TIMEOUT that I've set), I get the message that the scanning has stopped (STOPPING BLE SCAN)
Now I have implemented the leScanCallback as well (i.e the Device Scan Callback)
private ScanCallback leScanCallback =
new ScanCallback() {
#Override
public void onScanResult(int callbackType, ScanResult result) {
super.onScanResult(callbackType, result);
blefinder.append("SOMETHING GOT SCANNED?");
blefinder.append("\n"+result.getDevice().toString());
// leDeviceListAdapter.addDevice(result.getDevice());
// leDeviceListAdapter.notifyDataSetChanged();
}
};
Notice that I am not using a ListAdapter since I have no idea about that concept. Hence for starters I am just trying to dump the results in a TextView represented by blefinder . This blefinder prints all the other texts so there is nothing wrong with that TextView variable. When I ran using the, debugger, it is not entering into the leScanCallback piece of code definition at all, even after 30 seconds, after scanLeDevice() function is executed.
I am a little lost here. Is there something I may be missing or doing wrong. It is supposed to be a simple, list the ble/bt devices around my vicinity.
I am happy to share any further information if I have missed. Just let me know in the comments.

Assuming you've done with the permissions that I've mentioned in the comments, we can implement a clean bluetooth LE scanner object and then use it in the UI.
First we implement a result consumer interface in order to deliver the results to the consumers which call the BleScanner.scan() method.
public interface ScanResultConsumer {
public void onDeviceFound(BluetoothDevice device, byte[] scanRecord, int rssi);
public void onScanningStarted();
public void onScanningStopped();
}
Now we need to implement the scanner object that manages the scanning events:
public class BleScanner {
private static final String TAG = BleScanner.class.getSimpleName();
private BluetoothLeScanner leScanner = null;
private BluetoothAdapter bleAdapter = null;
private Handler uiHandler = new Handler(Looper.getMainLooper);
private ScanResultConsumer scanResultConsumer;
private boolean scanning = false;
private final ArrayList<BluetoothDevice> foundDeviceList = new ArrayList<>();
public BleScanner(Context context) {
final BluetoothManager bluetoothManager = (BluetoothManager)
context.getSystemService(Context.BLUETOOTH_SERVICE);
bleAdapter = bluetoothManager.getAdapter();
if(bleAdapter == null) {
Log.d(TAG, "No bluetooth hardware.");
}
else if(!bleAdapter.isEnabled()){
Log.d(TAG, "Blutooth is off.");
}
}
public void scan(ScanResultConsumer scanResultConsumer, long scanTime){
foundDeviceList.clear();
if (scanning){
Log.d(TAG, "Already scanning.");
return;
}
Log.d(TAG, "Scanning...");
if(leScanner == null){
leScanner = bleAdapter.getBluetoothLeScanner();
}
if(scanTimeMs > 0) {
uiHandler.postDelayed(()-> {
if (scanning) {
Log.d(TAG, "Scanning is stopping.");
if(leScanner != null)
leScanner.stopScan(scanCallBack);
else
Log.d(TAG,"Scanner null");
setScanning(false);
}
}, scanTimeMs);
}
this.scanResultConsumer = scanResultConsumer;
leScanner.startScan(scanCallBack);
setScanning(true);
}
private final ScanCallback scanCallBack = new ScanCallback() {
#Override
public void onScanResult(int callbackType, ScanResult result) {
super.onScanResult(callbackType, result);
if (!scanning){
return;
}
if(foundDeviceList.contains(result.getDevice())) {
// This device has already been found
return;
}
// New device found, add it to the list in order to prevent duplications
foundDeviceList.add(result.getDevice());
if(scanResultConsumer != null) {
uiHandler.post(() -> {
scanResultConsumer.onDeviceFound(result.getDevice(),
result.getScanRecord().getBytes(), result.getRssi());
});
}
}
};
public boolean isScanning(){
return scanning;
}
void setScanning(boolean scanning){
this.scanning = scanning;
uiHandler.post(() -> {
if(scanResultConsumer == null) return;
if(!scanning){
scanResultConsumer.onScanningStopped();
// Nullify the consumer in order to prevent UI crashes
scanResultConsumer = null;
} else{
scanResultConsumer.onScanningStarted();
}
});
}
}
Finally we can use this clean implementation in anywhere we need. But do note that a context must be provided in order to create a BleScanner object.
public class MainActivity extends AppCompatActivity {
private BleScanner bleScanner;
private Button buttonScan
// Other codes...
#Override
public void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Other codes...
bleScanner = new BleScanner(getApplicationContext());
// Other codes...
// For example if you want to start scanning on a button press
// Let's say you have a button called buttonScan and initiated it
buttonScan = findViewById(R.id.scan_button);
buttonScan.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
bleScanner.scan(new ScanResultConsumer {
#Override
public void onDeviceFound(BluetoothDevice device, byte[] scanRecord, int rssi) {
// TODO Here you have a newly found device, do something.
}
#Override
q public void onScanningStarted() {
// TODO Scanning has just started, you may want to make some UI changes.
}
#Override
public void onScanningStopped() {
// TODO Scanning has just stopped, you may want to make some UI changes.
}
});
}
});
}
}
Note: I written this code in a plain editor not in Android Studio. So there may be some errors, let me know if any.

First you should check if your app was granted the location permission(s) in the Settings app > Apps <your_app> > permissions. Some permissions (like ACCESS_*_LOCATION and BLUETOOTH_ADMIN) need to be requested at runtime and granted by the user through a popup. Normally you should get a SecurityException or a logcat warning when trying to execute code requiring permissions which your app doesn't have, but it's not uncommon for android to skip over error handling.
Consider using this method to start the scan in order check its result code for potential additional info about what is (not) going on.
You might also get some clues by logging all actions received in BTReceiver.onReceive(), not just action found.
Lastly check if the location settings on your device to ensure that bluetooth scanning is turned on (Settings app > location > wifi and bluetooth scanning )

GPS set to ON and app crashes at first start

I implemented an app that uses GPS location and so I am dealing with the permissions.
The app runs correctly, all locations are correctly performed.
When I install the application, the first fragment opens correctly and shows to user the request for GPS permission.
Behind that, I added also a dialog that requests to set ON the GPS in order to start the application.
If before first start (after installation) the GPS is set to OFF, when the app starts, it is shown the first fragment on background, the request for GPS permission and then the request to set ON the GPS inside settings.
If before first start (after installation) the GPS is set to ON, when the app starts, it is shown the first fragment on background, the request for GPS permission and app crashes maintaining the request for GPS permission active. If I press OK, I restart the application and all works properly.
Why this issue when GPS on settings is set to ON?
Here below a part of code:
On first fragment, onCreateView I wrote the following code for GPS permission:
mGoogleApiClient = new GoogleApiClient.Builder(getActivity())
.addApi(LocationServices.API)
.addOnConnectionFailedListener(this)
.addConnectionCallbacks(this)
.build();
if (ContextCompat.checkSelfPermission(getActivity(), Manifest.permission.ACCESS_FINE_LOCATION)
!= PackageManager.PERMISSION_GRANTED) {
if (ActivityCompat.shouldShowRequestPermissionRationale(getActivity(), Manifest.permission.ACCESS_FINE_LOCATION)) {
showAlert(getString(R.string.PermessoDisp), getString(R.string.PermessoDispTitle));
} else {
ActivityCompat.requestPermissions(getActivity(), new String[]{Manifest.permission.ACCESS_FINE_LOCATION},
MY_PERMISSION_REQUEST_LOCATION);
}
} else {
}
In the onStart() I have:
#Override
public void onStart() {
super.onStart();
if (isLocationEnabled()) {
mGoogleApiClient.connect();
} else {
showAlertGPSSettings();
}
}
where showAlertGPSSettings() is the method that ask user to set the GPS ON in order to use app.
And I have also:
#Override
public void onConnected(#Nullable Bundle bundle) {
locationRequest = LocationRequest.create();
locationRequest.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);
locationRequest.setInterval(1000);
locationRequest.setFastestInterval(500);
LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient, locationRequest, this);
}
#Override
public void onConnectionSuspended(int i) {
}
#Override
public void onConnectionFailed(#NonNull ConnectionResult connectionResult) {
}
#Override
public void onRequestPermissionsResult(int requestCode, #NonNull String[] permissions, #NonNull int[] grantResults) {
switch (requestCode) {
case MY_PERMISSION_REQUEST_LOCATION:
if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
} else {
}
}
}
When the app crashes (at first start when GPS is set to ON), I have the following error:
java.lang.SecurityException: Client must have ACCESS_FINE_LOCATION permission to request PRIORITY_HIGH_ACCURACY locations.
The row where the error is located, is inside the onConnected method:
LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient, locationRequest, this);
Any suggestion?

Did you add permission in your manifest?
android.permission.ACCESS_COARSE_LOCATION or android.permission.ACCESS_FINE_LOCATION.
This permissions are needed.

How to get a permission request in new ActivityResult API (1.3.0-alpha05)?

so, I tried to get a permission with the new registerForActivityResult() method and ask for with button click with .launch() and it doesn´t seem to be opening any window to ask for it.
I´m always getting false in registerForActivityResult().
// Permission to get photo from gallery, gets permission and produce boolean
private ActivityResultLauncher<String> mPermissionResult = registerForActivityResult(
new ActivityResultContracts.RequestPermission(),
new ActivityResultCallback<Boolean>() {
#Override
public void onActivityResult(Boolean result) {
if(result) {
Log.e(TAG, "onActivityResult: PERMISSION GRANTED");
} else {
Log.e(TAG, "onActivityResult: PERMISSION DENIED");
}
}
});
// Launch the permission window -- this is in onCreateView()
floatingActionButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
mPermissionResult.launch(Manifest.permission.ACCESS_BACKGROUND_LOCATION);
}
});
This is my LOG always: onActivityResult: PERMISSION DENIED

UPDATE
This answer works, but I found a better solution for permission requests with no open holes here.
From docs:
In your Activity/Fragment, create this field:
// Register the permissions callback, which handles the user's response to the
// system permissions dialog. Save the return value, an instance of
// ActivityResultLauncher, as an instance variable.
private ActivityResultLauncher<String> requestPermissionLauncher =
registerForActivityResult(new RequestPermission(), isGranted -> {
if (isGranted) {
// Permission is granted. Continue the action or workflow in your
// app.
} else {
// Explain to the user that the feature is unavailable because the
// features requires a permission that the user has denied. At the
// same time, respect the user's decision. Don't link to system
// settings in an effort to convince the user to change their
// decision.
}
});
Somewhere in the same Activity/Fragment:
if (ContextCompat.checkSelfPermission(
context, Manifest.permission.ACCESS_BACKGROUND_LOCATION) ==
PackageManager.PERMISSION_GRANTED) {
performAction(...);
} else if (shouldShowRequestPermissionRationale(...)) {
// In an educational UI, explain to the user why your app requires this
// permission for a specific feature to behave as expected. In this UI,
// include a "cancel" or "no thanks" button that allows the user to
// continue using your app without granting the permission.
showInContextUI(...);
} else {
// You can directly ask for the permission.
// The registered ActivityResultCallback gets the result of this request.
requestPermissionLauncher.launch(Manifest.permission.ACCESS_BACKGROUND_LOCATION);
}
If you are getting unreasonable "Permission denied" all the time, maybe you did not declare it in your manifest.xml?

Looking at Update to androidx.fragment:fragment:1.3.0-alpha08: registerForActivityResult not allowed after onCreate anymore. How to use after onCreate?,
private lateinit var checkLocationPermission: ActivityResultLauncher<Array<String>>
// Initialize checkLocationPermission in onAttach or onCreate.
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
checkLocationPermission = registerForActivityResult(
ActivityResultContracts.RequestMultiplePermissions()) { permissions ->
if (permissions[Manifest.permission.ACCESS_FINE_LOCATION] == true ||
permissions[Manifest.permission.ACCESS_COARSE_LOCATION] == true) {
initUserLocation()
} else {
// Permission was denied. Display an error message.
}
}
}
fun showMap() {
if (ActivityCompat.checkSelfPermission(requireContext(),
Manifest.permission.ACCESS_FINE_LOCATION) == PackageManager.PERMISSION_GRANTED ||
ActivityCompat.checkSelfPermission(requireContext(),
Manifest.permission.ACCESS_COARSE_LOCATION) == PackageManager.PERMISSION_GRANTED) {
initUserLocation()
} else {
checkLocationPermission.launch(arrayOf(Manifest.permission.ACCESS_FINE_LOCATION,
Manifest.permission.ACCESS_COARSE_LOCATION))
}
}
private fun initUserLocation() {
googleMap?.isMyLocationEnabled = true
}

java.lang.SecurityException: was not granted this permission: android.permission.WRITE_SETTINGS

I going to change some system setting in android and i use this code :
ContentResolver cr = getContentResolver();
Settings.System.putInt(cr, Settings.System.HAPTIC_FEEDBACK_ENABLED, 0);
this code used for change screen Brightness use Brightness sensor,
but in android 6 I get this exception
java.lang.SecurityException: com.vpn.sabalan was not granted this permission: android.permission.WRITE_SETTINGS.
i can use this method to get permission from user , but i need get permission programmetically can any one help me ?
private void showBrightnessPermissionDialog( )
{
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M && !android.provider.Settings.System.canWrite(this))
{
Intent intent = new Intent(android.provider.Settings.ACTION_MANAGE_WRITE_SETTINGS);
intent.setData(Uri.parse("package:"+getPackageName()));
startActivity(intent);
}
}

Update Android Marshmallow and Higher
You can start System settings to grant Write System Settings. Once this permission is grant by user you can set brightness without any issues
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
if (Settings.System.canWrite(this)) {
Intent intent = new Intent(Settings.ACTION_MANAGE_WRITE_SETTINGS);
intent.setData(Uri.parse("package:" + getPackageName()));
startActivity(intent);
}
}

Follow the step by step provided in documentation. It is very thorough.
https://developer.android.com/training/permissions/requesting.html
All you have to do is request permission, and override the callback for onRequestPermissionsResult to check if you got it or not. If you did, then you are good to go. You still need it in your manifest though or it won't work.
UPDATE to show details based on your comments.
public class MainActivity extends AppCompatActivity implements ActivityCompat.OnRequestPermissionsResultCallback{
private static final int REQUEST_WRITE_PERMISSION = 1001;
#Override
public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
if (requestCode == REQUEST_WRITE_PERMISSION && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
doFileWork();
}else{
//handle user denied permission, maybe dialog box to user
}
}
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
requestPermission();
}
private void requestPermission() {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
requestPermissions(new String[]{android.Manifest.permission.WRITE_EXTERNAL_STORAGE}, REQUEST_WRITE_PERMISSION);
} else {
doFileWork();
}
}
}
There are also many good libraries out there that wrap this callback context if you really want to go that route, but it isn't that complex. Make sure you also have write permission in your Manifest.

GoogleApiClient onConnected callback doesn't get called correctly

I'm trying to use the DriveApi in order to create some folders and upload a text file with some data for a user.
I've tried implementing the quick-start guide from (link), but it has a few fundamental issues:
The api gets connected at onResume so the user will get prompted to give access to the app immediately after he opens the app which is confusing and scary.
If you deny or press the back button at the consent screen, the onResume method will get called again and the consent screen will be shown one more time, leading to an infinite loop.
I would rather like to connect the api when the user actually needs to store data so that will make more sense to the user. I tried doing it like this:
ResultCallback<DriveFolder.DriveFolderResult> folderCreatedCallback = new
ResultCallback<DriveFolder.DriveFolderResult>() {
#Override
public void onResult(#NonNull DriveFolder.DriveFolderResult result) {
clearCurrentAction();
if (!result.getStatus().isSuccess()) {
Log.e(TAG, "Error while trying to create the folder");
return;
}
Log.d(TAG, "Created a folder: " + result.getDriveFolder().getDriveId());
}
};
public DriveApiHelper(GoogleApiClient mGoogleApiClient) {
this.mGoogleApiClient = mGoogleApiClient;
}
public void createBackupsFolder() {
currentAction = DriveActions.CREATING_FOLDER;
if (mGoogleApiClient.isConnected()) {
MetadataChangeSet changeSet = new MetadataChangeSet.Builder()
.setTitle("test").build();
Drive.DriveApi.getRootFolder(mGoogleApiClient).createFolder(
mGoogleApiClient, changeSet).setResultCallback(folderCreatedCallback);
} else {
mGoogleApiClient.connect();
}
}
and this is how my onResume and onConnected methods look like:
#Override
protected void onResume() {
super.onResume();
if (mGoogleApiClient == null) {
// Create the API client and bind it to an instance variable.
// We use this instance as the callback for connection and connection
// failures.
// Since no account name is passed, the user is prompted to choose.
mGoogleApiClient = new GoogleApiClient.Builder(this)
.addApi(Drive.API)
.addScope(Drive.SCOPE_FILE)
.addConnectionCallbacks(this)
.addOnConnectionFailedListener(this)
.build();
mDriveHelper = new DriveApiHelper(mGoogleApiClient);
}
//Log.d(TAG, mDriveHelper.getCurrentAction() + "");
Log.d("test", "Connected " + mGoogleApiClient.isConnected());
}
#Override
public void onConnected(Bundle connectionHint) {
Log.i(TAG, "API client connected.");
switch (mDriveHelper.getCurrentAction()) { //resume the last action
case CREATING_FOLDER:
mDriveHelper.createBackupsFolder();
break;
}
}
I was hoping that keeping a reference of what the user tried to do when the api was asked to connect, I can resume that action after the api successfully connected. This is the closest implementation I've got to fit my needs, but after actually clicking the 'Allow' button from the consent screen none of the api callbacks gets called (onConnected, onConnectionFailed).
I actually need to call the connect method one more time in order to get connected and also fire the onConnected successfully resuming the users' action.

Turns out that I forgot about overriding onActivityResult (it wasn't mentioned in the documentation at that time and I don't know if they included it now)
Just add:
#Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if (resultCode == RESULT_OK) {
if (requestCode == REQUEST_CODE_RESOLUTION) {
mGoogleApiClient.connect();
}
} else {
if (requestCode == REQUEST_CODE_RESOLUTION) {
mDriveHelper.dismissStatusDialog();
}
}
}