Android BluetoothLe Scan finds nothing

Question

I am trying to adapt the code from the Android example connectivity-samples-main\BluetoothLeGatt\Application\src\main\java\com\example\android\bluetoothlegatt\DeviceScanActivity.java

to my app I tried all the permissions, even the ones that are not required

    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>
    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>
        <uses-feature android:name="android.hardware.bluetooth_le" android:required="true"/>
    <uses-permission android:name="android.permission.BLUETOOTH" />
    <uses-permission android:name="android.permission.BLUETOOTH_SCAN" />
    <uses-permission android:name="android.permission.BLUETOOTH_CONNECT" />
    <uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />

instead of only

    <uses-feature android:name="android.hardware.bluetooth_le" android:required="true"/>
    <uses-permission android:name="android.permission.BLUETOOTH"/>
    <uses-permission android:name="android.permission.BLUETOOTH_ADMIN"/>

my code is

package com.embesystems.aresp32;

import static com.embesystems.aresp32.MainActivity.EXTRAS_DEVICE_ADDRESS;
import static com.embesystems.aresp32.MainActivity.EXTRAS_DEVICE_NAME;

import android.Manifest;
import android.annotation.SuppressLint;
import android.app.Activity;
import android.app.ListActivity;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothManager;
import android.content.Context;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.os.Bundle;
import android.os.Handler;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.BaseAdapter;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;

import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;

import com.embesystems.aresp32.databinding.ActivityScanBinding;

import java.util.ArrayList;

/**
 * Activity for scanning and displaying available Bluetooth LE devices.
 */
public class DeviceScanActivity extends AppCompatActivity {
    private static String TAG="MainActivity";
    private ActivityScanBinding binding;
    private LeDeviceListAdapter mLeDeviceListAdapter;
    private BluetoothAdapter mBluetoothAdapter;
    private boolean mScanning;
    private Handler mHandler;

    private static final int REQUEST_ENABLE_BT = 1;
    // Stops scanning after 10 seconds.
    private static final long SCAN_PERIOD = 10000;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        binding = ActivityScanBinding.inflate(getLayoutInflater());
//        setContentView(binding.getRoot());
//        setSupportActionBar(binding.toolbar);
        getSupportActionBar().setTitle(R.string.title_devices);

        binding.listview.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                Log.i(TAG, "Position=" + position);
                final BluetoothDevice device = mLeDeviceListAdapter.getDevice(position);
                if (device == null) return;
                if (mScanning) {
                    mBluetoothAdapter.stopLeScan(mLeScanCallback);
                    mScanning = false;
                }
                Intent resultIntent = new Intent();
                resultIntent.putExtra(EXTRAS_DEVICE_NAME, device.getName());
                resultIntent.putExtra(EXTRAS_DEVICE_ADDRESS, device.getAddress());
                setResult(Activity.RESULT_OK, resultIntent);
                finish();
            }
        });

        mHandler = new Handler();

        // Use this check to determine whether BLE is supported on the device.  Then you can
        // selectively disable BLE-related features.
        if (!getPackageManager().hasSystemFeature(PackageManager.FEATURE_BLUETOOTH_LE)) {
            Toast.makeText(this, R.string.ble_not_supported, Toast.LENGTH_SHORT).show();
            finish();
        }

        // Initializes a Bluetooth adapter.  For API level 18 and above, get a reference to
        // BluetoothAdapter through BluetoothManager.
        final BluetoothManager bluetoothManager =
                (BluetoothManager) getSystemService(Context.BLUETOOTH_SERVICE);
        mBluetoothAdapter = bluetoothManager.getAdapter();

        // Checks if Bluetooth is supported on the device.
        if (mBluetoothAdapter == null) {
            Toast.makeText(this, R.string.error_bluetooth_not_supported, Toast.LENGTH_SHORT).show();
            finish();
            return;
        }
//        mLeDeviceListAdapter.notifyDataSetChanged();
        scanLeDevice(true);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.scan_menu, menu);
        if (!mScanning) {
            menu.findItem(R.id.menu_stop).setVisible(false);
            menu.findItem(R.id.menu_scan).setVisible(true);
            // menu.findItem(R.id.menu_refresh).setActionView(null);
        } else {
            menu.findItem(R.id.menu_stop).setVisible(true);
            menu.findItem(R.id.menu_scan).setVisible(false);
            menu.findItem(R.id.menu_refresh).setActionView( R.layout.actionbar_indeterminate_progress);
        }
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.menu_scan:
                mLeDeviceListAdapter.clear();
                scanLeDevice(true);
                break;
            case R.id.menu_stop:
                scanLeDevice(false);
                break;
        }
        return true;
    }

    @Override
    protected void onResume() {
        super.onResume();
//            if (ActivityCompat.checkSelfPermission(this, Manifest.permission.BLUETOOTH_SCAN) != PackageManager.PERMISSION_GRANTED) {
//                // TODO: Consider calling
//                //    ActivityCompat#requestPermissions
//                // here to request the missing permissions, and then overriding
//                //   public void onRequestPermissionsResult(int requestCode, String[] permissions,
//                //                                          int[] grantResults)
//                // to handle the case where the user grants the permission. See the documentation
//                // for ActivityCompat#requestPermissions for more details.
//                String[] perms= new String[1];
//                perms[0]=Manifest.permission.BLUETOOTH_SCAN;
//                ActivityCompat.requestPermissions( this, perms,1);
////                return;
//            }
        // Ensures Bluetooth is enabled on the device.  If Bluetooth is not currently enabled,
        // fire an intent to display a dialog asking the user to grant permission to enable it.
        if (!mBluetoothAdapter.isEnabled()) {
            Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
//            if (ActivityCompat.checkSelfPermission(this, Manifest.permission.BLUETOOTH_CONNECT) != PackageManager.PERMISSION_GRANTED) {
//                // TODO: Consider calling
//                //    ActivityCompat#requestPermissions
//                // here to request the missing permissions, and then overriding
//                //   public void onRequestPermissionsResult(int requestCode, String[] permissions,
//                //                                          int[] grantResults)
//                // to handle the case where the user grants the permission. See the documentation
//                // for ActivityCompat#requestPermissions for more details.
//                return;
//            }
            startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
        }

        // Initializes list view adapter.
        mLeDeviceListAdapter = new LeDeviceListAdapter();
        binding.listview.setAdapter(mLeDeviceListAdapter);
        mLeDeviceListAdapter.notifyDataSetChanged();
        scanLeDevice(true);
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        // User chose not to enable Bluetooth.
        if (requestCode == REQUEST_ENABLE_BT && resultCode == Activity.RESULT_CANCELED) {
            finish();
            return;
        }
        super.onActivityResult(requestCode, resultCode, data);
    }

    @Override
    protected void onPause() {
        super.onPause();
        scanLeDevice(false);
        mLeDeviceListAdapter.clear();
        mLeDeviceListAdapter.notifyDataSetChanged();
    }

    private void scanLeDevice(final boolean enable) {
        if (enable) {
            Log.d(TAG, "scanLeDevice");
            // Stops scanning after a pre-defined scan period.
            mHandler.postDelayed(new Runnable() {
                @Override
                public void run() {
                    mScanning = false;
                    mBluetoothAdapter.stopLeScan(mLeScanCallback);
                    invalidateOptionsMenu();
                }
            }, SCAN_PERIOD);

            mScanning = true;
//            if (ActivityCompat.checkSelfPermission(this, Manifest.permission.BLUETOOTH_SCAN) != PackageManager.PERMISSION_GRANTED) {
//                // TODO: Consider calling
//                //    ActivityCompat#requestPermissions
//                // here to request the missing permissions, and then overriding
//                //   public void onRequestPermissionsResult(int requestCode, String[] permissions,
//                //                                          int[] grantResults)
//                // to handle the case where the user grants the permission. See the documentation
//                // for ActivityCompat#requestPermissions for more details.
//                String[] perms= new String[1];
//                perms[0]=Manifest.permission.BLUETOOTH_SCAN;
//                ActivityCompat.requestPermissions( this, perms,1);
////                return;
//            }
            Log.d(TAG, "Commence à scanner...");
            mBluetoothAdapter.startLeScan(mLeScanCallback);
        } else {
            mScanning = false;
            Log.d(TAG, "Arrête de scanner.");
            mBluetoothAdapter.stopLeScan(mLeScanCallback);
        }
        invalidateOptionsMenu();
    }

    // Adapter for holding devices found through scanning.
    private class LeDeviceListAdapter extends BaseAdapter {
        private ArrayList<BluetoothDevice> mLeDevices;
        private LayoutInflater mInflator;

        public LeDeviceListAdapter() {
            super();
            mLeDevices = new ArrayList<BluetoothDevice>();
            mInflator = DeviceScanActivity.this.getLayoutInflater();
            Log.d(TAG, "Init ListAdapter...");
        }

        public void addDevice(BluetoothDevice device) {
            if(!mLeDevices.contains(device)) {
                mLeDevices.add(device);
            }
        }

        public BluetoothDevice getDevice(int position) {
            return mLeDevices.get(position);
        }

        public void clear() {
            mLeDevices.clear();
        }

        @Override
        public int getCount() {
            return mLeDevices.size();
        }

        @Override
        public Object getItem(int i) {
            return mLeDevices.get(i);
        }

        @Override
        public long getItemId(int i) {
            return i;
        }

        @Override
        public View getView(int i, View view, ViewGroup viewGroup) {
            ViewHolder viewHolder;
            // General ListView optimization code.
            if (view == null) {
                view = mInflator.inflate(R.layout.listitem_device, null);
                viewHolder = new ViewHolder();
                viewHolder.deviceAddress = (TextView) view.findViewById(R.id.device_address);
                viewHolder.deviceName = (TextView) view.findViewById(R.id.device_name);
                view.setTag(viewHolder);
            } else {
                viewHolder = (ViewHolder) view.getTag();
            }

            BluetoothDevice device = mLeDevices.get(i);
            final String deviceName = device.getName();
            if (deviceName != null && deviceName.length() > 0)
                viewHolder.deviceName.setText(deviceName);
            else
                viewHolder.deviceName.setText(R.string.unknown_device);
            viewHolder.deviceAddress.setText(device.getAddress());

            return view;
        }
    }

    // Device scan callback.
    private BluetoothAdapter.LeScanCallback mLeScanCallback =
            new BluetoothAdapter.LeScanCallback() {

        @Override
        public void onLeScan(final BluetoothDevice device, int rssi, byte[] scanRecord) {
            runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    Log.d(TAG, "Ajoute à liste");
                    mLeDeviceListAdapter.addDevice(device);
                    mLeDeviceListAdapter.notifyDataSetChanged();
                }
            });
        }
    };

    static class ViewHolder {
        TextView deviceName;
        TextView deviceAddress;
    }
}

I use the

    compileSdk 32
...
        minSdk 21
        targetSdk 31

but I also tried targetSdk 28 and 29

So far without success. The debug indicates that it start scanning but no results. I have BLE Scanner app that finds my ble iot device and connects to it. So the issue is with my Android code / manifest confifg. Any ideas? thanks

Answer 1

Some of the Bluetooth permissions you have specified are runtime permissions. However, all the code for querying these runtime permissions is commented out.

It is very likely that your application simply does not have the required permissions and the results are therefore empty.