BLE scan does not discover device

My code is as follows->

manifest

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.root.securityalert">

<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:roundIcon="@mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="@style/AppTheme">
<activity android:name=".DeviceScanActivity" android:label="Activity2" />
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />

<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:label="@string/app_name" android:name=".BlueTooth"/>
</application>
<uses-feature android:name="android.hardware.bluetooth_le" android:required="false"/>
<uses-permission android:name="android.permission.BLUETOOTH" />
<uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
</manifest>


deviceScanActivity

class DeviceScanActivity extends AppCompatActivity/ListActivity/ {

public BluetoothAdapter mBluetoothAdapter;
public /*final*/ BluetoothManager mBluetoothManager;

ArrayList<ViewHolder> arrayOfUsers2 = new ArrayList<ViewHolder>();
private boolean mScanning;

private Handler mHandler;

ArrayList<String> mylist = new ArrayList<String>();
private static final int REQUEST_ENABLE_BT = 1;
// Stops scanning after 10 seconds.
private static final long SCAN_PERIOD = 50000;
private static final int PERMISSION_REQUEST_COARSE_LOCATION = 456;

UsersAdapter adapter;
@Override
public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);
setContentView(R.layout.main);
//getActionBar().setTitle("abc");

mHandler = new Handler();

requestPermissions(new String{Manifest.permission.ACCESS_COARSE_LOCATION}, PERMISSION_REQUEST_COARSE_LOCATION);
// 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.
mBluetoothManager =
(BluetoothManager) getSystemService(Context.BLUETOOTH_SERVICE);
mBluetoothAdapter = mBluetoothManager.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;
}
if( !mBluetoothAdapter.isEnabled())
{
Intent enableBluetooth = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(enableBluetooth, 1);
}
if( !mBluetoothAdapter.isDiscovering()) {
Intent discoverableIntent =
new Intent(BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE);
discoverableIntent.putExtra(BluetoothAdapter.EXTRA_DISCOVERABLE_DURATION, 300);
startActivity(discoverableIntent);
}
// Construct the data source

ArrayList<ViewHolder> arrayOfUsers = new ArrayList<ViewHolder>();

// Create the adapter to convert the array to views

adapter = new UsersAdapter(this, arrayOfUsers);


ListView listView = (ListView) findViewById(R.id.mobile_list);
listView.setAdapter(adapter);
ViewHolder newUser2 = new ViewHolder("adtv2","vvg2");
adapter.add(newUser2);

}


private void scanLeDevice(final boolean enable) {
if (enable) {
// Stops scanning after a pre-defined scan period.
ViewHolder newUser2 = new ViewHolder("adtv2","vvg2");
adapter.add(newUser2);
mHandler.postDelayed(new Runnable() {
@Override
public void run() {
mScanning = false;
mBluetoothAdapter.stopLeScan(mLeScanCallback);


if(arrayOfUsers2.isEmpty())
{
ViewHolder currentX=new ViewHolder("No devices ","found");
adapter.add(currentX);
}
else {
Iterator<ViewHolder> it = arrayOfUsers2.iterator();
while (it.hasNext()) {
ViewHolder currentX = it.next();
adapter.add(currentX);
}
}
// Do something with the value

}
}, SCAN_PERIOD);

mScanning = true;
mBluetoothAdapter.startLeScan(mLeScanCallback);
} else {
mScanning = false;
mBluetoothAdapter.stopLeScan(mLeScanCallback);
}
//invalidateOptionsMenu();
}
@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String permissions, @NonNull int grantResults) {
switch (requestCode) {
case PERMISSION_REQUEST_COARSE_LOCATION: {
if (grantResults[0] == PackageManager.PERMISSION_GRANTED) {
// Permission granted, yay! Start the Bluetooth device scan.
scanLeDevice(true);
} else {
// Alert the user that this application requires the location permission to perform the 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() {
//mLeDeviceListAdapter.addDevice(device);
//mLeDeviceListAdapter.notifyDataSetChanged();

//ViewHolder newUser = new ViewHolder("Nathan", "San Diego");
String deviceName=null, deviceAddress=null;
if(device!=null)
deviceName= device.getName();
if (!(deviceName != null && deviceName.length() > 0))
deviceName = "unknown device";
if(device!=null)
deviceAddress= device.getAddress();
ViewHolder newUser = new ViewHolder(deviceName, deviceAddress);
ViewHolder newUser2 = new ViewHolder("adtv","vvg");
//if(!arrayOfUsers2.contains(newUser))
arrayOfUsers2.add(newUser);
adapter.add(newUser);
}
});
}
};
public class UsersAdapter extends ArrayAdapter<ViewHolder> {


public UsersAdapter(Context context, ArrayList<ViewHolder> users) {

super(context, 0, users);

}



@Override

public View getView(int position, View convertView, ViewGroup parent) {

// Get the data item for this position

ViewHolder user = getItem(position);


// Check if an existing view is being reused, otherwise inflate the view

if (convertView == null) {

convertView = LayoutInflater.from(getContext()).inflate(R.layout.bt_details, parent, false);

}

// Lookup view for data population

TextView tvName = (TextView) convertView.findViewById(R.id.DeviceName);

TextView tvHome = (TextView) convertView.findViewById(R.id.DeviceAddress);

// Populate the data into the template view using the data object

tvName.setText(user.deviceName);

tvHome.setText(user.deviceAddress);

// Return the completed view to render on screen

return convertView;

}

}
public class ViewHolder {
String deviceName;
String deviceAddress;

public ViewHolder(String device, String __address) {
this.deviceName =device;
this.deviceAddress= __address;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
ViewHolder a = (ViewHolder) o;
return Objects.equals(deviceAddress, a.deviceAddress);
}
}



}


}});
ViewHolder newUser2 = new ViewHolder("adtv2","vvg2");
adapter.add(newUser2);

}


private void scanLeDevice(final boolean enable) {
if (enable) {
// Stops scanning after a pre-defined scan period.
ViewHolder newUser2 = new ViewHolder("adtv2","vvg2");
adapter.add(newUser2);
mHandler.postDelayed(new Runnable() {
@Override
public void run() {
mScanning = false;
mBluetoothAdapter.stopLeScan(mLeScanCallback);


if(arrayOfUsers2.isEmpty())
{
ViewHolder currentX=new ViewHolder("No devices ","found");
adapter.add(currentX);
}
else {
Iterator<ViewHolder> it = arrayOfUsers2.iterator();
while (it.hasNext()) {
ViewHolder currentX = it.next();
adapter.add(currentX);
}
}
// Do something with the value

}
}, SCAN_PERIOD);

mScanning = true;
mBluetoothAdapter.startLeScan(mLeScanCallback);
} else {
mScanning = false;
mBluetoothAdapter.stopLeScan(mLeScanCallback);
}

}
@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String permissions, @NonNull int grantResults) {
switch (requestCode) {
case PERMISSION_REQUEST_COARSE_LOCATION: {
if (grantResults[0] == PackageManager.PERMISSION_GRANTED) {
// Permission granted, yay! Start the Bluetooth device scan.
scanLeDevice(true);
} else {
// Alert the user that this application requires the location permission to perform the 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() {

String deviceName=null, deviceAddress=null;
if(device!=null)
deviceName= device.getName();
if (!(deviceName != null && deviceName.length() > 0))
deviceName = "unknown device";
if(device!=null)
deviceAddress= device.getAddress();
ViewHolder newUser = new ViewHolder(deviceName, deviceAddress);
ViewHolder newUser2 = new ViewHolder("adtv","vvg");
//if(!arrayOfUsers2.contains(newUser))
arrayOfUsers2.add(newUser);
adapter.add(newUser);
}
});
}
};
public class UsersAdapter extends ArrayAdapter<ViewHolder> {


public UsersAdapter(Context context, ArrayList<ViewHolder> users) {

super(context, 0, users);

}



@Override

public View getView(int position, View convertView, ViewGroup parent) {

// Get the data item for this position

ViewHolder user = getItem(position);


// Check if an existing view is being reused, otherwise inflate the view

if (convertView == null) {

convertView = LayoutInflater.from(getContext()).inflate(R.layout.bt_details, parent, false);

}

// Lookup view for data population

TextView tvName = (TextView) convertView.findViewById(R.id.DeviceName);

TextView tvHome = (TextView) convertView.findViewById(R.id.DeviceAddress);

// Populate the data into the template view using the data object

tvName.setText(user.deviceName);

tvHome.setText(user.deviceAddress);

// Return the completed view to render on screen

return convertView;

}

}
public class ViewHolder {
String deviceName;
String deviceAddress;

public ViewHolder(String device, String __address) {
this.deviceName =device;
this.deviceAddress= __address;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
ViewHolder a = (ViewHolder) o;
return Objects.equals(deviceAddress, a.deviceAddress);
}
}



}


I am trying to scan for nearby bluetooth devices using BLE API.I had tested with this code,it was working till today morning.But I got 2 new devices and am putting this code on both of them and testing. They are not discovering each other.Also it is not discovering my laptop. Earlier I could discover other devices nearby. Hope they are not nearby now.Both of them are discovering same one device but not discovering each other.
build.gradle(ModuleApp)

apply plugin: 'com.android.application'
apply plugin: 'kotlin-android'

android {
compileSdkVersion 26
defaultConfig {
applicationId "com.example.root.securityalert"
minSdkVersion 23
targetSdkVersion 26
versionCode 1
versionName "1.0"
testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}
}
}

dependencies {
implementation fileTree(include: ['*.jar'], dir: 'libs')
implementation 'com.android.support:appcompat-v7:26.1.0'
implementation 'com.android.support.constraint:constraint-layout:1.0.2'
testImplementation 'junit:junit:4.12'
androidTestImplementation 'com.android.support.test:runner:1.0.1'
androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.1'
compile 'io.reactivex.rxjava2:rxandroid:2.0.0'
compile 'io.reactivex.rxjava2:rxjava:2.0.0'
implementation 'com.android.support:design:27.0.2'-this line is in red(error)
compile "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
}
repositories {
mavenCentral()
}


Build.gradle(Project:xyz)

// Top-level build file where you can add configuration options common to all sub-projects/modules.

buildscript {
ext.kotlin_version = '1.2.50'

repositories {
google()
jcenter()
}
dependencies {
classpath 'com.android.tools.build:gradle:3.1.3'
classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
compile 'io.reactivex.rxjava2:rxandroid:2.0.0'
compile 'io.reactivex.rxjava2:rxjava:2.0.0'
// NOTE: Do not place your application dependencies here; they belong
// in the individual module build.gradle files
}
}

allprojects {
repositories {
google()
jcenter()
}
}

task clean(type: Delete) {
delete rootProject.buildDir
}


logcat error

build failed 213ms
Run build 90ms
Load build 3ms
Configure build 78ms
Load projects 6ms
rootProject
Configure project : 61ms
Apply plugin org.gradle.help-tasks 1ms
Apply script build.gradle 53ms--- this line is in red(error)


Also I get this error

Could not find method compile() for arguments [io.reactivex.rxjava2:rxjava:2.0.0] on object of type org.gradle.api.internal.artifacts.dsl.dependencies.DefaultDependencyHandler.


1 Answer
1

Make sure you have the API levels ironed out because most of the Android BLE constructs are > API 21. The one where adapter.startLeScan{} is for lower API devices and that maybe the reason why new devices are not being able to detect the other devices. I created a simple BLE scanner with Rx using Kotlin. This makes it easier to handle and schedule on to threads.

adapter.startLeScan{}

You can configure it using the Builder and setting stopCallback with a condition would stop the scan upon hitting that condition.

Builder

stopCallback

import android.bluetooth.BluetoothAdapter
import android.bluetooth.BluetoothDevice
import android.bluetooth.le.ScanCallback
import android.bluetooth.le.ScanFilter
import android.bluetooth.le.ScanResult
import android.bluetooth.le.ScanSettings
import android.os.Build
import android.support.annotation.RequiresApi
import io.reactivex.*
import io.reactivex.android.schedulers.AndroidSchedulers
import io.reactivex.schedulers.Schedulers
import org.jetbrains.anko.bluetoothManager

class BleScannerFlowable private constructor(
private val adapter: BluetoothAdapter,
private val stopCallback: ((BluetoothDevice) -> Boolean)? = null,
private val scanFilter: Array<out ScanFilter>? = null,
private val scanSettings: ScanSettings? = null
): FlowableOnSubscribe<BluetoothDevice> {

override fun subscribe(e: FlowableEmitter<BluetoothDevice>) {
if (isAboveLollipop()) {
setupSubscriber21(e)
} else {
setupSubscriber(e)
}
}

private fun setupSubscriber(emitter: FlowableEmitter<BluetoothDevice>) {
adapter.startLeScan { device, rssi, scanRecord ->
if (stopCallback?.invoke(device) == true) {
adapter.stopLeScan { device, rssi, scanRecord ->
emitter.onComplete()
}
}
emitter.onNext(device)
}
}

@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
private fun setupSubscriber21(emitter: FlowableEmitter<BluetoothDevice>) {
val isFilterSet = scanFilter?.isNotEmpty() == true
val filters = if (isFilterSet) scanFilter!!.toMutableList() else mutableListOf()
adapter.bluetoothLeScanner?.startScan(filters, scanSettings, ScanCaller(emitter))
}

@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
private inner class ScanCaller(private val emitter: FlowableEmitter<BluetoothDevice>) : ScanCallback() {
override fun onScanFailed(errorCode: Int) {
emitter.onError(Throwable("Scan failed with code $errorCode"))
}

override fun onScanResult(callbackType: Int, result: ScanResult?) {
if (result != null && result.device != null) {
if (stopCallback?.invoke(result.device) == true) {
adapter.bluetoothLeScanner?.stopScan(this)
emitter.onComplete()
} else {
emitter.onNext(result.device)
}
}
}
}

class Builder(private val adapter: BluetoothAdapter) {
private var scanFilter: Array<out ScanFilter>? = null
private var stopCallback: ((BluetoothDevice) -> Boolean)? = null
private var settingsBuilder: ScanSettings.Builder? = null
private var scanSettings: ScanSettings? = null

@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
fun setFilterByName(name: String) : Builder {
setScanFilters(ScanFilter.Builder()
.setDeviceName(name)
.build())
return this
}

@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
fun setScanFilters(vararg scanFilter: ScanFilter) : Builder{
this.scanFilter = scanFilter
return this
}

@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
fun setScanMode(scanMode: ScanModes) : Builder{
getSettingsBuilder().setScanMode(scanMode.settingId)
return this
}

fun setStopCallback(function: (BluetoothDevice) -> Boolean) : Builder {
this.stopCallback = function
return this
}

@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
fun setScanSettings(scanSettings: ScanSettings) : Builder {
this.scanSettings = scanSettings
return this
}

@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
fun build(): Flowable<BluetoothDevice> =
Flowable.create(BleScannerFlowable(adapter,
stopCallback,
scanFilter,
scanSettings ?: settingsBuilder?.build()),
BackpressureStrategy.LATEST)

fun buildLower(): Flowable<BluetoothDevice> =
Flowable.create(BleScannerFlowable(adapter, stopCallback),
BackpressureStrategy.LATEST)

@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
private fun getSettingsBuilder() : ScanSettings.Builder {
if (settingsBuilder == null) {
settingsBuilder = ScanSettings.Builder()
}
return settingsBuilder!!
}
}

}


@RequiresApi(Build.VERSION_CODES.LOLLIPOP)
enum class ScanModes(val settingId: Int) {
LOW_LATENCY(ScanSettings.SCAN_MODE_LOW_LATENCY),
LOW_POWER(ScanSettings.SCAN_MODE_LOW_POWER),
BALANCED(ScanSettings.SCAN_MODE_BALANCED),
OPPORTUNISTIC(ScanSettings.SCAN_MODE_BALANCED)
}

fun startScanning() {
val adapter = applicationContext.bluetoothManager.adapter ?: return
val bleScanner = if (isAboveLollipop()) {
BleScannerFlowable.Builder(adapter)
.setScanMode(ScanModes.BALANCED)
.setStopCallback { it.name == "MyBleDevice" }
.build()
} else {
BleScannerFlowable.Builder(adapter)
.setStopCallback { it.name == "MyBleDevice" }
.buildLower()
}

bleScanner
.observeOn(AndroidSchedulers.mainThread())
.subscribe({
// do something with the bluetooth device
}, {
// handle error
it.printStackTrace()
}, {
// do on finish scan
})
}

fun isAboveLollipop() = Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP


what language is this,does not look like java? I read java 5 years back.Now it may have changed. Is this BLE compatible?
– mithun
Jun 28 at 7:23

This is Kotlin as mentioned in the comment. Yes it is inverse compatible with Java and is meant for BLE scanning
– HawkPriest
Jun 28 at 7:32

Kotlin

I created a class RX_BLE.kt and copied the whole content, but it is showing errors on some imports.
– mithun
Jun 28 at 7:33

can you give me a link where I can study about kotlin in short
– mithun
Jun 28 at 7:36

You need to configure kotlin in project. If you have the latest android studio, you have to go to tools->kotlin->configure kotlin in project and select the project or module for kotlin support. You can find basic introduction to android kotlin here: developer.android.com/kotlin. Better tutorial is with a simple example is: android.jlelse.eu/…
– HawkPriest
Jun 28 at 7:45

tools->kotlin->configure kotlin in project

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