Running an IntentService in BroadcastReceiver using AlarmManager

Question

I want to call a Service in my Receiver class which extends BroadcastReceiver but the service didn't start and I got this error:

FATAL EXCEPTION: main java.lang.RuntimeException: Unable to
    start receiver com.example.ahmed.service.AlarmReceiver: 
    java.lang.NullPointerException: Attempt to invoke virtual 
    method 'java.lang.String 
    android.content.Context.getPackageName()' on a null 
    object reference

In my MainActivity, I call the alarm manager:

 // Calendar settings for AlarmReceiver
        Calendar cur_cal = new GregorianCalendar();
        cur_cal.setTimeInMillis(System.currentTimeMillis());//set the current time and date for this calendar
        Calendar cal = new GregorianCalendar();
        cal.add(Calendar.DAY_OF_YEAR, cur_cal.get(Calendar.DAY_OF_YEAR));
        cal.set(Calendar.HOUR_OF_DAY, 8);
        cal.set(Calendar.MINUTE, 07);
        cal.set(Calendar.SECOND, cur_cal.get(Calendar.SECOND));
        cal.set(Calendar.MILLISECOND, cur_cal.get(Calendar.MILLISECOND));
        cal.set(Calendar.DATE, cur_cal.get(Calendar.DATE));
        cal.set(Calendar.MONTH, cur_cal.get(Calendar.MONTH));

        // Retrieve a PendingIntent that will perform a broadcast
        alarmIntent = new Intent(this, AlarmReceiver.class);
        pendingIntent = PendingIntent.getBroadcast(this, 0, alarmIntent, 0);

        AlarmManager alarm = (AlarmManager) getSystemService(Context.ALARM_SERVICE);
        alarm.setRepeating(AlarmManager.RTC_WAKEUP, cal.getTimeInMillis(), 30 * 1000, pendingIntent);


// When you click Start sensing button
    public void onSensingButtonClickedToStart(final View view) {
        if (!SensorEvent.isSensing) {
            SensorEvent.isSensing = true;

            manager = (AlarmManager) getSystemService(Context.ALARM_SERVICE);
            int interval = 10000;
            manager.setRepeating(AlarmManager.RTC_WAKEUP, System.currentTimeMillis(), interval, pendingIntent);
            Toast.makeText(this, "Sensing On", Toast.LENGTH_SHORT).show();
        }
    }

    // when you click Stop sensing button
    public void onSensingButtonClickedToStop(final View view) {
        if (SensorEvent.isSensing) {

            manager = (AlarmManager) getSystemService(Context.ALARM_SERVICE);
            manager.cancel(pendingIntent);
            Toast.makeText(this, "Sensing Off", Toast.LENGTH_SHORT).show();
            SensorEvent.isSensing = false;
        }
    }

My Service

public class Sense8 extends IntentService {

    public static Accelerometer accelerometer;
    public static Gyroscope gyroscope;
    public static Light light;
    public static Magnetometer magnetometer;
    Context context;

    /**
     * Creates an IntentService.  Invoked by your subclass's constructor.
     *
     */
    public Sense8(String name) {
        super(name);
    }

    public Sense8(){
        super("Sense8");
    }

    @Override
    protected void onHandleIntent(Intent intent) {

        Log.d("accelerometer.isSensing", SensorEvent.isSensing + "");
        if (accelerometer.isSensing) {
            accelerometer = new Accelerometer(context);
            gyroscope = new Gyroscope(context);
            light = new Light(context);
            magnetometer = new Magnetometer(context);
            Toast.makeText(context, "I'm running instead of some sensors being captured", Toast.LENGTH_SHORT).show();
            Log.d("toast", "I'm running instead of some sensors being captured");
            startSensing();
        }
    }

    public static void startSensing() {
        accelerometer.start();
        gyroscope.start();
        light.start();
        magnetometer.start();
    }

    public void stopSensing() {
        accelerometer.stop();
        gyroscope.stop();
        light.stop();
        magnetometer.stop();

    }
}

In my Receiver class, I only call the IntentService:

 @Override
    public void onReceive(Context c, Intent intent) {


        Intent service = new Intent(c, Sense8.class);
        c.startService(service);
}

But in vain, it doesn't even start and hit me directly with the above error

What am I doing wrong? Can someone help me implement this the right way.

EDIT

the guys gave me the right solution for the first problem but now I get the same error after pushing the sensing button

Here is the SensorEvent:

public class SensorEvent implements SensorEventListener {

    public static boolean isSensing;
    SensorManager mSensorManager;
    Sensor mSensor;
    DataWriter fileWriter;
    Constants.SensorType sensorType;
    Context context;


    private SensorEvent()
    {}

    private static SensorEvent INSTANCE = null;

    public static SensorEvent getInstance()
    {
        if (INSTANCE == null)
        {   INSTANCE = new SensorEvent();
        }
        return INSTANCE;
    }

    public static SensorEvent getInstance(Context context, Constants.SensorType sensorType)
    {
        if (INSTANCE == null)
        {   INSTANCE = new SensorEvent(context, sensorType);
        }
        return INSTANCE;
    }


    public SensorEvent(Context context, Constants.SensorType sensorType) {
        this.sensorType = sensorType;

        this.context = context;
        this.mSensorManager = (SensorManager) context.getSystemService(Context.SENSOR_SERVICE);
        this.mSensor = mSensorManager.getDefaultSensor(sensorType.getType());
      //  this.isSensing = true;
    }


    public void start() {
        isSensing = true;
        fileWriter = new DataWriter(sensorType);
        mSensorManager.registerListener(this, mSensor, SensorManager.SENSOR_DELAY_NORMAL);
    }

    public void stop() {
        try {
            fileWriter.finish();
        } catch (IOException e) {
            e.printStackTrace();
        }
        isSensing = false;
    }


    @Override
    public void onSensorChanged(android.hardware.SensorEvent event) {

        try {
            if (isSensing) {
                fileWriter.append(event);

            } else {
                fileWriter.finish();
                mSensorManager.unregisterListener(this);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    @Override
    public void onAccuracyChanged(Sensor sensor, int accuracy) {

    }


}

In your `BroadcastReceiver`, you're apparently using a null `Context` reference that you declared outside of the `onReceive()` method. Instead, use the `Context` passed into `onReceive()`. That is, change `context` to `c`, on both lines. — Mike M., Jun 25 '16 at 08:05
Possible duplicate of [What is a NullPointerException, and how do I fix it?](http://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do-i-fix-it) — Sufian, Jun 26 '16 at 01:38

score 0 · Answer 1 · answered Jun 25 '16 at 08:07

0

just change :

 @Override 
    public void onReceive(Context c, Intent intent) {


        Intent service = new Intent(context, Sense8.class);
        context.startService(service);
}

to

 @Override 
    public void onReceive(Context c, Intent intent) {


        Intent service = new Intent(c, Sense8.class);
        c.startService(service);
}

You haven't assigned you context to parameter c. So you are trying to start service on null reference.

answered Jun 25 '16 at 08:07

Krupal Shah

8,949
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Yes indeed, silly mistake i am sorry. now the app opens up but after i hit the **onSensingButtonClickedToStart** button i get, the app starts sensing and i don't get the following toast `Toast.makeText(context, "I'm running instead of some sensors being captured", Toast.LENGTH_SHORT).show();` If you allow me i will edit my question and provide you with the right class. My aim is to capture sensor data in given intervals and i am trying to implement the IntentService because someone here on StackOverflow said that this allows running a service even though the app is closed – Ahmed Hamed Jun 25 '16 at 11:08
@ahmedhamed I can't know what you have written here until you explain it nicely. A question will not get answer here until it fails you understand what's going on to others. I think this makes sense. Put proper explanation of what you are doing, why and which error you got - with complete stacktraces and logs. – Krupal Shah Jun 25 '16 at 11:41
You are right, okay i have an app which collects sensors, write them to SD card then send them via FTP. The app uses alarm manager and sensor manager and all the adequate classes, it works fine and generate a file every 10 or 20 sec as specified in the interval. the problem is with the activity life cycle, when i push home button it continues to work that's fine, but when i close the app it stops collecting data. Thats why i had to implement the IntentService but now once i push the start sending button it stays a couple of seconds then i get the **the application has stopped** – Ahmed Hamed Jun 25 '16 at 12:02

Running an IntentService in BroadcastReceiver using AlarmManager

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