BeaconManager being passed Null context

[graham768]

I compiled the source in my build.gradle and copied the code from the 2.x API Transition guide into a new Android project to test the library for the first time. I saw an issue similar to this, but the library was known to be edited. I have not changed any aspect of the library in this case.

Expected behavior

I was hoping the program would run and check for the default UUID given in the source code.

public class MainActivity extends AppCompatActivity implements BeaconConsumer {

    protected static final String TAG = "MainActivity";
    private BeaconManager beaconManager = BeaconManager.getInstanceForApplication(this);

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        beaconManager.bind(this);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        beaconManager.unbind(this);
    }

    @Override
    public void onBeaconServiceConnect() {
        beaconManager.setRangeNotifier(new RangeNotifier() {
            @Override
            public void didRangeBeaconsInRegion(Collection<Beacon> beacons, Region region) {
                if (beacons.size() > 0) {
                    Log.i(TAG, "The first beacon I see is about "+beacons.iterator().next().getDistance()+" meters away.");
                }
            }
        });

        try {
            beaconManager.startRangingBeaconsInRegion(new Region("myRangingUniqueId", Identifier.parse("2F234454-CF6D-4A0F-ADF2-F4911BA9FFA6"), Identifier.parse("1"), null));
        } catch (RemoteException e) {   }
    }
}

Actual behavior

java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.content.Context.getApplicationContext()' on a null object reference
                                                                                   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2327)
                                                                                   at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
                                                                                   at android.app.ActivityThread.-wrap11(ActivityThread.java)
                                                                                   at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
                                                                                   at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                                   at android.os.Looper.loop(Looper.java:148)
                                                                                   at android.app.ActivityThread.main(ActivityThread.java:5422)
                                                                                   at java.lang.reflect.Method.invoke(Native Method)
                                                                                   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                                                   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
                                                                                Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.content.Context.getApplicationContext()' on a null object reference
                                                                                   at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:107)
                                                                                   at com.example.ben.beacontesting.MainActivity.<init>(MainActivity.java:22)
                                                                                   at java.lang.Class.newInstance(Native Method)
                                                                                   at android.app.Instrumentation.newActivity(Instrumentation.java:1067)
                                                                                   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2317)
                                                                                   at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
                                                                                   at android.app.ActivityThread.-wrap11(ActivityThread.java) 
                                                                                   at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
                                                                                   at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                                   at android.os.Looper.loop(Looper.java:148) 
                                                                                   at android.app.ActivityThread.main(ActivityThread.java:5422) 
                                                                                   at java.lang.reflect.Method.invoke(Native Method) 
                                                                                   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
                                                                                   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 

Steps to reproduce this behavior

Start a new project. compile 2.9.2, paste API Migration code in MainActivity, and run

Mobile device model and OS version

Nexus 6P 6.0.1

Android Beacon Library version

2.9.2

IMPORTANT: This forum is reserved for feature requests or reproducible bugs with the library itself. If you need help with using the library with your project, please open a new question on StackOverflow.com.

[graham768]

Fixed by instantiating beaconManager inside onCreate

public class MainActivity extends AppCompatActivity implements BeaconConsumer {

    protected static final String TAG = "MainActivity";
    private BeaconManager beaconManager;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        beaconManager = BeaconManager.getInstanceForApplication(this);
        beaconManager.bind(this);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        beaconManager.unbind(this);
    }

    @Override
    public void onBeaconServiceConnect() {
        beaconManager.setRangeNotifier(new RangeNotifier() {
            @Override
            public void didRangeBeaconsInRegion(Collection<Beacon> beacons, Region region) {
                if (beacons.size() > 0) {
                    Log.i(TAG, "The first beacon I see is about "+beacons.iterator().next().getDistance()+" meters away.");
                }
            }
        });

        try {
            beaconManager.startRangingBeaconsInRegion(new Region("myRangingUniqueId", Identifier.parse("2F234454-CF6D-4A0F-ADF2-F4911BA9FFA6"), Identifier.parse("1"), null));
        } catch (RemoteException e) {   }
    }
}

[davidgyoung]

Thanks for this report @graham768. I have updated the documentation so that the BeaconManager is not shown as being constructed in an instance variable declaration. Hopefully this will save other folks the same trouble you had.