Android: strange npe on MapView onDestroy inside an activity

Question

I'm using a mapview inside an activity, but I'm receiving a strange null pointer exception that I can't seem to pinpoint the cause of.

xml:

<com.google.android.gms.maps.MapView
                    xmlns:map="http://schemas.android.com/apk/res-auto"
                    android:id="@+id/myMapView"
                    android:layout_width="match_parent"
                    android:layout_height="156dp"
                    map:cameraZoom="16"
                    map:liteMode="true"
                    android:visibility="invisible"
                    />

Then inside the activity:

private MapView mMapView;

initialization in onCreate:

mMapView = (MapView) findViewById(R.id.myMapView);

and overriding the methods:

mMapView.onCreate(savedInstanceState);

@Override
protected void onDestroy() {
    super.onDestroy();
    mMapView.onDestroy();

}


@Override
public void onLowMemory() {
    super.onLowMemory();
    mMapView.onLowMemory();

}


@Override
protected void onPause() {
    super.onPause();
    mMapView.onPause();

}


@Override
protected void onResume() {
    super.onResume();
    mMapView.onResume();


}

And I'm continually receiving a crash on the mapview onDestroy method whose stacktrace is as follows:

java.lang.RuntimeException: Unable to destroy activity {myActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.util.LinkedList.isEmpty()' on a null object reference
                                                                           at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:3831)
                                                                           at android.app.ActivityThread.handleDestroyActivity(ActivityThread.java:3849)
                                                                           at android.app.ActivityThread.-wrap5(ActivityThread.java)
                                                                           at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1398)
                                                                           at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                           at android.os.Looper.loop(Looper.java:148)
                                                                           at android.app.ActivityThread.main(ActivityThread.java:5417)
                                                                           at java.lang.reflect.Method.invoke(Native Method)
                                                                           at com.android.internal.os.ZygoteInit$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 'boolean java.util.LinkedList.isEmpty()' on a null object reference
                                                                           at com.google.android.gms.dynamic.zza.zzeJ(Unknown Source)
                                                                           at com.google.android.gms.dynamic.zza.onDestroy(Unknown Source)
                                                                           at com.google.android.gms.maps.MapView.onDestroy(Unknown Source)
                                                                           at myActivity.onDestroy(myActivity.java:454)
                                                                           at android.app.Activity.performDestroy(Activity.java:6422)
                                                                           at android.app.Instrumentation.callActivityOnDestroy(Instrumentation.java:1142)
                                                                           at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:3818)
                                                                           at android.app.ActivityThread.handleDestroyActivity(ActivityThread.java:3849) 
                                                                           at android.app.ActivityThread.-wrap5(ActivityThread.java) 
                                                                           at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1398) 
                                                                           at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                           at android.os.Looper.loop(Looper.java:148) 
                                                                           at android.app.ActivityThread.main(ActivityThread.java:5417) 
                                                                           at java.lang.reflect.Method.invoke(Native Method) 
                                                                           at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
                                                                           at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

Given that mmapview is initialized at the start of onCreate from the xml and exists fine up until the onDestroy, what could be the cause of this null pointer?

What if you remove `super.onDestroy();` or move this line below ? — Shree Krishna, Apr 17 '16 at 09:52
@ShreeKrishna yes, I have - that was one of the first things that I tried when I first started getting the error — Jon, Apr 17 '16 at 10:14

score 4 · Accepted Answer · answered Apr 19 '16 at 10:46

4

Turns out in the end that the reason was because I had the mapview.oncreate inside an if statement that wasn't being executed. As soon as I moved it to the very beginning of the oncreate method the error stopped occcuring.

answered Apr 19 '16 at 10:46

Jon

7,941
9
53
105

score 2 · Answer 2 · answered Apr 17 '16 at 09:57

2

If you are sure it's fine till onDestroy() I suggest doing like this,

@Override
protected void onDestroy() {
    if(mMapView != null) {
        mMapView.onDestroy();
    }
    super.onDestroy();
}

answered Apr 17 '16 at 09:57

Shree Krishna

8,474
6
40
68

score 0 · Answer 3 · answered Apr 17 '16 at 11:05

I don't think you have to worry about calling onDestroy() on your view. I could be wrong but it should be done anyway when the activity is destroyed being a view on the XML.

If you would have other objects (adapters or presenters) you initialized on onCreate() it could be a good idea to clean them up (call release methods/set them to null or whatever is needed)

Apart for that a good rule that I follow is for onPause/onDestroy what Shree Krishna suggests: clean up your resources and then call super.

@Override
    protected void onPause() {
        // clean up your resources in respect to your onResume
        ...
        super.onPause();
    }

@Override
protected void onDestroy() {
    // clean up your resources in respect of onCreate
    ...
    super.onDestroy();
}

Android: strange npe on MapView onDestroy inside an activity

3 Answers3