Develop Reference

Android Bluetooth LE Scan how to check if device is out of range?

I have faced with the issue using startScan method of BluetoothLeScanner a BLE device was found, but when I turned off BLE device my phone still shows this device as turned on !!
I have tried to use:
private ScanCallback mScanCallback = new ScanCallback() {
#Override
public void onScanResult(int callbackType, ScanResult result) {
Log.i("ScanCallback", String.format("onScanResult(int callbackType[%d], ScanResult result)", callbackType));
final BluetoothDevice btDevice = result.getDevice();
if (btDevice == null){
Log.e("ScanCallback", "Could not get bluetooth device");
return;
}
final String macAddress = btDevice.getAddress();
if (callbackType == ScanSettings.CALLBACK_TYPE_MATCH_LOST) {
// NOTE: I've never got here
final BluetoothDevice outOfRangeDevice = mBtDevices.get(macAddress);
...
} else {
...
}
}
...
};
Guy, I have not found solution how to detect that BLE device is lost in other resources like (Android SDK reference, forums, stackoverflow and etc) (:
Any help will be appreciated !!

During googling and exploring the Android Documentations I have figured out how to detect if device is out of range. I would like to share my solution how I did it:
...
public void scanBLEDevices(final boolean enable) {
if(mLeScanner == null) {
Log.d(TAG, "Could not get LEScanner object");
throw new InternalError("Could not get LEScanner object");
}
if (enable) {
startLeScan();
} else {
stopLeScan(false);
}
}
private void startLeScan() {
Log.i(TAG, "startLeScan(BluetoothLeScanner mLeScanner)");
mScanning = true;
mInRangeBtDevices.clear();
if (mStartScanCallback != null) {
mHandler.removeCallbacks(mStartScanCallback);
}
if (Build.VERSION.SDK_INT < 21) {
mBluetoothAdapter.startLeScan(mLeScanCallback);
} else {
mLeScanner.startScan(mScanFilters, mScanSettings, mScanCallback);
}
mStopScanCallback = new Runnable() {
#Override
public void run() {
stopLeScan(true);
}
};
mHandler.postDelayed(mStopScanCallback, SCAN_PERIOD);
}
private void stopLeScan(final boolean isContinueAfterPause) {
Log.i(TAG, "stopLeScan(BluetoothLeScanner mLeScanner)");
mScanning = false;
if (mStopScanCallback != null) {
mHandler.removeCallbacks(mStopScanCallback);
}
removeOutOfRangeDevices();
if (Build.VERSION.SDK_INT < 21) {
mBluetoothAdapter.stopLeScan(mLeScanCallback);
} else {
mLeScanner.stopScan(mScanCallback);
}
if (isContinueAfterPause) {
mStartScanCallback = new Runnable() {
#Override
public void run() {
startLeScan();
}
};
mHandler.postDelayed(mStartScanCallback, SCAN_PAUSE);
}
}
private void removeOutOfRangeDevices() {
final Set<String> outOfRangeDevices = new HashSet<>();
for (String btAddress : mBtDevices.keySet()) {
if (!mInRangeBtDevices.contains(btAddress)) {
outOfRangeDevices.add(btAddress);
}
}
for (String btAddress : outOfRangeDevices) {
final BluetoothDevice outOfRangeDevice = mBtDevices.get(btAddress);
mBtDevicesRSSI.remove(btAddress);
mBtDevices.remove(btAddress);
}
}
...
Explanation:
As you can see I have added on each scanning period mInRangeBtDevices collection that will keep all devices found during the current scanning.
When I stop scanning, I am also removing out of range device from previous lists that is not available anymore using one additional helper collection outOfRangeDevices
I think this example would be usefull and you will be able to integrate it in your own code

This one is looking good (JAVA):
As I understood, you need to implement startLeScan().
Find BLE devices
To find BLE devices, you use the startLeScan() method. This method takes a BluetoothAdapter.LeScanCallback as a parameter. You must implement this callback, because that is how scan results are returned. Because scanning is battery-intensive, you should observe the following guidelines:
As soon as you find the desired device, stop scanning.
Never scan on a loop, and set a time limit on your scan. A device that was previously available may have moved out of range, and continuing to scan drains the battery.
The following snippet shows how to start and stop a scan:
public class DeviceScanActivity extends ListActivity {
private BluetoothAdapter mBluetoothAdapter;
private boolean mScanning;
private Handler mHandler;
// Stops scanning after 10 seconds.
private static final long SCAN_PERIOD = 10000;
...
private void scanLeDevice(final boolean enable) {
if (enable) {
// Stops scanning after a pre-defined scan period.
mHandler.postDelayed(new Runnable() {
#Override
public void run() {
mScanning = false;
mBluetoothAdapter.stopLeScan(mLeScanCallback);
}
}, SCAN_PERIOD);
mScanning = true;
mBluetoothAdapter.startLeScan(mLeScanCallback);
} else {
mScanning = false;
mBluetoothAdapter.stopLeScan(mLeScanCallback);
}
...
}
...}
Consider checking this tutorial as well.
Also this one.

Ble scanning callback only get called several times then stopped

I have 2 phones with Android 5.0.2, they both installed the latest Radius Beacon's App: Locate Beacon, meanwhile, I turned on 2 IBeacon sender, and can see the RSSI keep changing in both phone with the App.
But when I tried to write some sample code to simulate above situation, I found the ble scan callback always stop get called after called 2 or 3 times, I initially suspect the 'Locate Beacon' may use different way, so I tried with 2 kinds of API, one is for old 4.4, and another is the new way introduced in android 5, but both the same behavior(but all running on android 5).
the 4.4 one:
public class MainActivity extends Activity {
private BluetoothAdapter mBluetoothAdapter;
private static final String LOG_TAG = "BleCollector";
private TextView calledTimesTextView = null;
private int calledTimes = 0;
// Device scan callback.
private BluetoothAdapter.LeScanCallback mLeScanCallback = new BluetoothAdapter.LeScanCallback() {
#Override
public void onLeScan(final BluetoothDevice device, int rssi,
byte[] scanRecord) {
calledTimes++;
runOnUiThread(new Runnable() {
#Override
public void run() {
calledTimesTextView.setText(Integer.toString(calledTimes));
}
});
Log.e(LOG_TAG, "in onScanResult, " + " is coming...");
}
};
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
calledTimesTextView = (TextView) findViewById(R.id.CalledTimes);
mBluetoothAdapter = ((BluetoothManager) getSystemService(Context.BLUETOOTH_SERVICE))
.getAdapter();
mBluetoothAdapter.startLeScan(mLeScanCallback);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}}
And the 5.0.2:
public class MainActivity extends Activity {
private BluetoothAdapter mBluetoothAdapter = null;
private BluetoothLeScanner mLescanner;
private ScanCallback mLeScanCallback;
private static final String LOG_TAG = "BleFingerprintCollector";
private TextView calledTimesTextView = null;
private int calledTimes = 0;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
calledTimesTextView = (TextView) findViewById(R.id.CalledTimes);
this.mBluetoothAdapter = ((BluetoothManager) getSystemService(Context.BLUETOOTH_SERVICE))
.getAdapter();
this.mLescanner = this.mBluetoothAdapter.getBluetoothLeScanner();
ScanSettings bleScanSettings = new ScanSettings.Builder().setScanMode(
ScanSettings.SCAN_MODE_LOW_LATENCY).build();
this.mLeScanCallback = new ScanCallback() {
#Override
public void onScanResult(int callbackType, ScanResult result) {
calledTimes++;
runOnUiThread(new Runnable() {
#Override
public void run() {
calledTimesTextView.setText(Integer
.toString(calledTimes));
}
});
Log.e(LOG_TAG, "in onScanResult, " + " is coming...");
}
#Override
public void onBatchScanResults(List<ScanResult> results) {
}
#Override
public void onScanFailed(int errorCode) {
}
};
this.mLescanner.startScan(null, bleScanSettings, this.mLeScanCallback);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}}
They are very simple and just show a counter in UI, proved finally always stopped at 2 or 3.
I've played this ble advertising receiving before on a SamSung note 2 with android 4.4 device, it works perfectly, the callback get called every second.
then anyone can help? why Radius' Locate Beacon works well here?

Different Android devices behave differently when scanning for connectable BLE advertisements. On some devices (e.g. the old Nexus 4), the scanning APIs only get one callback per scan for transmitters sending a connectable advertisement, whereas they get a scan callback for every advertisement for non-connectable advertisements. Newer devices (e.g. the Nexus 5 and most built after 2015) provide a scan callback every single advertisement regardless of whether it is connectable.
The Locate app you mention uses the open source Android Beacon Library to detect beacons. It is built on top of the same scanning APIs you show in your question, but it gets around this problem by defining a scan period (1.1 seconds by default in the foreground) and stopping and restarting a scan at this interval. Stopping and restarting the scan causes Android to send a new callback.
A few other notes here:
This issue of getting multiple scan callbacks for connectable devices applies to both the 4.x and 5.x scanning APIs.
It is unclear whether the difference in delivering scan callbacks for connectable advertisements on different devices is due to Android firmware differences or bluetooth hardware chipset differences.
There doesn't seem to be a way to detect if a device requires a scan restart to get additional callbacks for connectable advertisements, so if you are targeting a wide variety of devices, you need to plan to stop and restart scanning.
Using Android's raw scanning APIs is a great way to understand how BLE beacons work. But there are lots of complexities with working with BLE beacons (this is just one example) which is why using a SDK like the Android Beacon Library is a good choice to keep you from pulling your hair out.
Full disclosure: I am the author of the Locate app in the lead developer on the Android Beacon Library open source project.

David - Are you sure that scan callback gets called for every non-connectable advertisement. I have a Xiaomi Redmi 3 and another Nexus 5 phone running Android 6.0. I have a BLE sensor that at every 1 minute interval sends the data. These phones appearing as central BLE device should receive and process the data from the sensor. I can see from an Over the Air (OTA) BLE capture device that it the sensor is sending data every 1 minute. However both phones seems to process data for few minutes at 1 minute interval but after that stop processing for 4 - 6 minutes and then start processing agenter code hereain.
Time interval of phone processing on looks like this
1 min, 2 min, 3 min, 8min, 9min, 10min, 11 min
So after processing 3 packets at 1 minute interval, either phone will stop processing for 4 -6 minutes.
Here is code that does the processing.
public class BluetoothDataReader {
private final Context context;
public BluetoothDataReader(Context context) {
this.context = context;
}
public void startReading() {
BluetoothAdapter btAdapter = getBluetoothAdapter();
if (btAdapter == null) return;
BluetoothLeScanner scanner = btAdapter.getBluetoothLeScanner();
ScanSettings settings = new ScanSettings.Builder()
.setScanMode(ScanSettings.SCAN_MODE_LOW_LATENCY)
.build();
scanner.startScan(Collections.<ScanFilter>emptyList(), settings, new ScanRecordReader());
}
public void uploadScanBytes(SensorDataUploader sensorDataUploader, int count) {
BluetoothAdapter btAdapter = getBluetoothAdapter();
if (btAdapter == null) return;
BluetoothLeScanner scanner = btAdapter.getBluetoothLeScanner();
ScanSettings settings = new ScanSettings.Builder()
.setScanMode(ScanSettings.SCAN_MODE_BALANCED)
.setCallbackType(ScanSettings.CALLBACK_TYPE_ALL_MATCHES)
.build();
// scanner.startScan(Arrays.asList(new ScanFilter.Builder().setDeviceAddress("26:50:26:50:26:50").build()), settings, new LimitedScanRecordReader(sensorDataUploader, count, scanner));
scanner.startScan(Collections.<ScanFilter>emptyList(), settings, new LimitedScanRecordReader(sensorDataUploader, count, scanner));
}
#Nullable
private BluetoothAdapter getBluetoothAdapter() {
BluetoothAdapter btAdapter = BluetoothAdapter.getDefaultAdapter();
if(btAdapter == null){
Log.i(BluetoothDataReader.class.getName(), "No bluetooth adapter available");
return null;
}
if(!btAdapter.isEnabled()){
Log.i(BluetoothDataReader.class.getName(), "Enable bluetooth adapter");
Intent enableBluetooth = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
context.startActivity(enableBluetooth);
}
return btAdapter;
}
private class LimitedScanRecordReader extends ScanCallback {
private final int limit;
private final BluetoothLeScanner scanner;
private int scanRecordRead = 0;
private final SensorDataUploader sensorDataUploader;
private LimitedScanRecordReader( SensorDataUploader sensorDataUploader, int limit, BluetoothLeScanner scanner) {
this.limit = limit;
this.scanner = scanner;
this.sensorDataUploader = sensorDataUploader;
}
#Override
public void onScanResult(int callbackType, ScanResult result) {
// if(scanRecordRead++ < limit) {
// if(result.getDevice().getAddress().equals("A0:E6:F8:01:02:03")) {
// if(result.getDevice().getAddress().equals("C0:97:27:2B:74:D5")) {
if(result.getDevice().getAddress().equals("A0:E6:F8:01:02:03")) {
long timestamp = System.currentTimeMillis() -
SystemClock.elapsedRealtime() +
result.getTimestampNanos() / 1000000;
byte[] rawBytes = result.getScanRecord().getBytes();
Log.i(DataTransferService.class.getName(), "Raw bytes: " + byteArrayToHex(rawBytes));
sensorDataUploader.upload(timestamp, rawBytes);
}
// }else {
// scanner.stopScan(this);
// }
}
public String byteArrayToHex(byte[] a) {
StringBuilder sb = new StringBuilder(a.length * 2);
for(byte b: a)
sb.append(String.format("%02x", b & 0xff));
return sb.toString();
}
public void onScanFailed(int errorCode) {
Log.i(DataTransferService.class.getName(), "Error code is:" + errorCode);
}
public void onBatchScanResults(java.util.List<android.bluetooth.le.ScanResult> results) {
Log.i(DataTransferService.class.getName(), "Batch scan results");
}
}
private class ScanRecordReader extends ScanCallback {
#Override
public void onScanResult(int callbackType, ScanResult result) {
byte []rawBytes = result.getScanRecord().getBytes();
Log.i(DataTransferService.class.getName(), "Raw bytes: " + byteArrayToHex(rawBytes ));
// Map<ParcelUuid, byte[]> serviceData = result.getScanRecord().getServiceData();
// for(ParcelUuid uuid : serviceData.keySet()) {
// Log.i(DataTransferService.class.getName(), uuid.toString() + ":" + byteArrayToHex(serviceData.get(uuid)));
// }
// Log.i(DataTransferService.class.getName(),result.toString());
}
public String byteArrayToHex(byte[] a) {
StringBuilder sb = new StringBuilder(a.length * 2);
for(byte b: a)
sb.append(String.format("%02x", b & 0xff));
return sb.toString();
}
public void onScanFailed(int errorCode) {
Log.i(DataTransferService.class.getName(), "Error code is:" + errorCode);
}
public void onBatchScanResults(java.util.List<android.bluetooth.le.ScanResult> results) {
Log.i(DataTransferService.class.getName(), "Batch scan results");
}
}
}

Blutooth LE Scan

I am developing a demo app to scan Blutooth Le devices. But startLeScan() returns null. and I am not getting any device name. I have tried using normal scan it shows up fine. I am adding my snippet here
private void scanLeDevice(final boolean enable) {
if (enable) {
// Stops scanning after a pre-defined scan period.
new Handler().postDelayed(new Runnable() {
#Override
public void run() {
mScanning = false;
mTxtInfo.setText("Stopped Scanning.");
mBluetoothAdapter.stopLeScan(mLeScanCallback);
}
}, SCAN_PERIOD);
mScanning = true;
mTxtInfo.setText("Started Scanning...");
mBluetoothAdapter.startLeScan(mLeScanCallback);
} else {
mTxtInfo.setText("Stopped Scanning.");
mScanning = false;
mBluetoothAdapter.stopLeScan(mLeScanCallback);
}
}
This is my function to start Le scan.
// 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() {
mTxtInfo.setText("Detected devices: " + device.getName());
Toast.makeText(MainActivity.this,
"Detected devices: " + device.getName(),
Toast.LENGTH_LONG).show();
}
});
}
};
this is the callback. And its showing me
07-04 12:50:17.833: D/BluetoothAdapter(3564): startLeScan(): null
Would appreciate any help.

The Problem there is that you are trying to use
startLeScan(callback)
without setting the Uuid parameter. So the BluetoothAdapter code it's doing something like:
startLeScan(null, callback)
on the back and printing
"startLeScan:" + Uuid.
Which for you is null.

how to deal with datastreams in android

I want to analysis the heart rate of a heart rate monitor. For that I want to save the last used device and compare it to the found devices. Because it takes a while to find devices, mDevice remains null. What do I have to do to update mDevice properly?
private ArrayList<BluetoothDevice> mDeviceList;
private BluetoothAdapter mBluetoothAdapter;
private boolean mScanning;
private Handler mHandler;
private BluetoothDevice mDevice;
private static final int REQUEST_ENABLE_BT = 1;
// Stops scanning after 10 seconds.
private static final long SCAN_PERIOD = 10000;
#Override
protected void onStart() {
super.onStart();
// 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);
startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
}
// Initializes list view adapter.
mDeviceList = new ArrayList<BluetoothDevice>();
scanLeDevice(true);
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this);
final String adress = prefs.getString(getString(R.string.device_address), "");
for(BluetoothDevice b : mDeviceList){
if(b.getAddress().equals(adress)){
mDevice = b;
}
}
if(mDevice != null)
Log.e(TAG, mDevice.getAddress());
}
taken from the google manual:
private void scanLeDevice(final boolean enable) {
if (enable) {
// 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;
mBluetoothAdapter.startLeScan(mLeScanCallback);
} else {
mScanning = false;
mBluetoothAdapter.stopLeScan(mLeScanCallback);
}
invalidateOptionsMenu();
}
// 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() {
if(!mDeviceList.contains(device)){
mDeviceList.add(device);
}
}
});
}
};
I hope these are enough information. If something is missing, feel free to ask

The scan is a background activity your trying to look at the results straight after you start it rather than waiting for it to finish. You may want to put your checking code into the onLeScan call-back directly and stopping the scan as soon as you see the device you want.
You could also try not doing the scan all together if you already have the details for the device just try going straight to connect. The details of if you need to scan before you connect are not at all clear from the documentation so you need to be prepared to experiment a bit as it's still all far too flaky.

Just move your code where you try to find the last device (everything in onStart() after SharedPreferences prefs...) to after you have already found devices, for example at the end of your runnable (after invalidateOptionsMenu();)

NoClassDefFoundError during class load for BLE scanning callback

I am keep on getting the NoClassDefFoundError when my class is loaded.
The code is taken from BluetoothLeGatt project -
http://developer.android.com/samples/BluetoothLeGatt/project.html
My code:
// Device scan callback.
private BluetoothAdapter.LeScanCallback mLeScanCallback =
new BluetoothAdapter.LeScanCallback() { //java.lang.NoClassDefFoundError...
#Override
public void onLeScan(final BluetoothDevice device,
final int rssi, final byte[] scanRecord) {
runOnUiThread(new Runnable() {
#Override
public void run() {
String msg= device.getAddress();
Log.d(TAG,msg);
addItems(msg);
}
});
}
};
Someone suggested that the error is because my device doesn't support BLE but I want to get rid of this error for any device. So if it doesn't support BLE feature then simply skip this error else continue with the call to this BluetoothAdapter.LeScanCallback.
NOTE:
See this my previous SO post for more clarification.
Putting the BLE feature check as the first line onCreate() doesn't stop the crash --
#Override
public void onCreate(Bundle savedInstanceState) {
if (!bleCheck()) {
Toast.makeText(getApplicationContext(), R.string.ble_not_supported,
Toast.LENGTH_SHORT).show();
finish();
}
//Rest of the code
//Call to BLE Scan on button click that causes error..
}
private boolean bleCheck() {
boolean result = false;
if (getPackageManager().
hasSystemFeature(PackageManager.FEATURE_BLUETOOTH_LE)){
result = true;
}
return result;
}

As BluetoothAdapter.LeScanCallback was Added in API level 18 ; Source, this code would need a API level check also. Here's how i have gone about this, not declared the callback as private but under the condition:
boolean apiJBorAbove = android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.JELLY_BEAN_MR2 ? true
: false;
boolean isBleAvailable = getPackageManager().hasSystemFeature(
PackageManager.FEATURE_BLUETOOTH_LE) ? true : false;
// Use this check to determine whether BLE is supported on the device.
if (isBleAvailable && apiJBorAbove) {
// 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();
// Ensures Bluetooth is available on the device and it is enabled.
// If not, displays a dialog requesting user permission to enable
// Bluetooth.
if (mBluetoothAdapter == null || !mBluetoothAdapter.isEnabled()) {
startActivity(new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE));
}
BluetoothAdapter.LeScanCallback mLeScanCallback =
new BluetoothAdapter.LeScanCallback() {
#Override
public void onLeScan(final BluetoothDevice device,
final int rssi, final byte[] scanRecord) {
runOnUiThread(new Runnable() {
#Override
public void run() {
String msg= device.getAddress();
// Log.d(TAG,msg);
// addItems(msg);
}
});
}
};
}
The NoClassDefFoundError is due to the API , not on the basis of PackageManager.FEATURE_BLUETOOTH_LE.