Google Play控制台报告应用程序崩溃，我无法复制

Question

Google Play Console in Android Vitals reports provides me with this information

java.lang.RuntimeException: 
  at android.app.ActivityThread.performLaunchActivity (ActivityThread.java:2955)
  at android.app.ActivityThread.handleLaunchActivity (ActivityThread.java:3030)
  at android.app.ActivityThread.-wrap11 (Unknown Source)
  at android.app.ActivityThread$H.handleMessage (ActivityThread.java:1696)
  at android.os.Handler.dispatchMessage (Handler.java:105)
  at android.os.Looper.loop (Looper.java:164)
  at android.app.ActivityThread.main (ActivityThread.java:6938)
  at java.lang.reflect.Method.invoke (Native Method)
  at com.android.internal.os.Zygote$MethodAndArgsCaller.run (Zygote.java:327)
  at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:1374)
Caused by: java.lang.NullPointerException: 
  at com.golendukhin.whitenoise.GridAdapter.getCount (GridAdapter.java:52)
  at android.widget.GridView.setAdapter (GridView.java:243)
  at com.golendukhin.whitenoise.FoldersGridActivity.onCreate (FoldersGridActivity.java:60)
  at android.app.Activity.performCreate (Activity.java:7183)
  at android.app.Instrumentation.callActivityOnCreate (Instrumentation.java:1220)
  at android.app.ActivityThread.performLaunchActivity (ActivityThread.java:2908)

As I have understood this happens because getCount method of grid adapter returns null value. Hense, grid adapter does not work. Hense, whole acrivity is not created. Only Samsung devices has such a problem.

First, I've tryed to create same emulated device with same Android version, RAM and ARM. Emulator works absolutely great. No mistakes.

Then I have added some tests to be sure getCount works and activity is created.

@RunWith(AndroidJUnit4.class)
public class GridViewTest {

    @Rule
    public ActivityTestRule<FoldersGridActivity> foldersGridActivityTestRule  = new  ActivityTestRule<>(FoldersGridActivity.class);

    @Test
    public void ensureGridAdapterIsNotNull() {
        FoldersGridActivity foldersGridActivity = foldersGridActivityTestRule.getActivity();
        View view = foldersGridActivity.findViewById(R.id.grid_view);
        GridView gridView = (GridView) view;
        GridAdapter gridAdapter = (GridAdapter) gridView.getAdapter();
        assertThat(gridAdapter, notNullValue());
    }

    @Test
    public void ensureArrayAdapterInGridActivityIsNotEmpty() {
        FoldersGridActivity foldersGridActivity = foldersGridActivityTestRule.getActivity();
        View view = foldersGridActivity.findViewById(R.id.grid_view);
        GridView gridView = (GridView) view;
        GridAdapter gridAdapter = (GridAdapter) gridView.getAdapter();
        assertTrue(gridAdapter.getCount() > 0 );
    }

    @Test
    public void gridViewIsVisibleAndClickable() {
        onData(anything()).inAdapterView(withId(R.id.grid_view)).atPosition(0).perform(click());
        onView(withId(R.id.toolbar_title_text_view)).check(matches(withText("rain")));
    }
}

And again all emulated devices successfully pass tests. Then I have added FireBase TestLab and launched my tests on Galaxy S9 real device with Android 8. All tests are passed.

Code of adapter. Yes, I have overriten getCount() method even though it does not make sence.

public class GridAdapter extends ArrayAdapter<TracksFolder> {
    @BindView(R.id.folder_text_view) TextView textView;
    @BindView(R.id.grid_item_image_view) ImageView imageView;

    private ArrayList<TracksFolder> tracksFolders;
    private Context context;

    GridAdapter(Context context, int resource, ArrayList<TracksFolder> tracksFolders) {
        super(context, resource, tracksFolders);
        this.tracksFolders = tracksFolders;
        this.context = context;
    }

    /**
     * @return grid item, customized via TracksFolder class instance
     */
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        if (convertView == null) {
            convertView = LayoutInflater.from(context).inflate(R.layout.grid_item, parent, false);
        }
        ButterKnife.bind(this, convertView);

        String folderName = tracksFolders.get(position).getFolderName();
        int imageResource = tracksFolders.get(position).getImageResource();
        textView.setText(folderName);
        imageView.setImageResource(imageResource);

        return convertView;
    }

    /**
     * Added to possibly avoid NPE on multiple devices
     * Could not reproduce this error
     * @return size of tracksFolders
     */
    @Override
    public int getCount() {
        return tracksFolders.size();
    }
}

So, I have got a couple of question: First, does this crash reports mean that this crash happens every time Sumsung owner launches app? Since some Samsung devices persist in statistic, I assume no. Second, what am I supposed to do to somehow reproduce this mistake and eventually fix the bug.

I understand question is too broad, but I will really appreciate any help, because I absolutely don't know what to do next.

Entry class. Uses adapter

import android.content.Intent;
import android.content.SharedPreferences;
import android.content.res.Resources;
import android.content.res.TypedArray;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.AdapterView;
import android.widget.Button;
import android.widget.GridView;

import com.google.firebase.crash.FirebaseCrash;

import java.util.ArrayList;
import butterknife.BindArray;
import butterknife.BindView;
import butterknife.ButterKnife;

import static com.golendukhin.whitenoise.SharedPreferencesUtils.writeToSharedPreferences;

public class FoldersGridActivity extends AppCompatActivity {
    @BindView(R.id.grid_view) GridView gridView;
    @BindArray(R.array.labels) String[] foldersName;
    @BindView(R.id.toolbar_like_button) Button toolbarLikeButton;
    @BindView(R.id.toolbar_back_button) Button toolbarBackButton;

    private ArrayList<TracksFolder> tracksFolders;

    /**
     * Binds all UI views
     * Defines variables to feed adapter and listeners
     * Initializes grid adapter, sets number of columns via phone in portrait or landscape orientation
     * Sets onclick listener for every grid item
     * Sets onclick for toolbar "like" button
     */
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.folders_grid_view);
        ButterKnife.bind(this);

        if (getIntent().getExtras() != null) { //activity is triggered via on back pressed
            Bundle bundle = getIntent().getExtras();
            tracksFolders = (ArrayList<TracksFolder>) bundle.getSerializable("tracksFolders");
        } else if (savedInstanceState != null) { //this happens after screen is rotated
            tracksFolders = (ArrayList<TracksFolder>) savedInstanceState.getSerializable("tracksFolders");
        } else { //this happens if app is launched by user
            tracksFolders = getTracksFolders();
            initService();
        }

        toolbarBackButton.setVisibility(View.GONE);

        GridAdapter gridAdapter;
        gridAdapter = new GridAdapter(this, R.id.grid_view, tracksFolders);
        gridView.setNumColumns(getResources().getInteger(R.integer.columns_number));
        gridView.setAdapter(gridAdapter);
        FirebaseCrash.log("Activity created");

        gridView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                Bundle bundle = new Bundle();
                bundle.putSerializable("tracksFolders", tracksFolders);
                bundle.putInt("folderPosition", position);
                Intent intent = new Intent(FoldersGridActivity.this, TracksListActivity.class);
                intent.putExtras(bundle);
                startActivity(intent);
            }
        });

        toolbarLikeButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Bundle bundle = new Bundle();
                bundle.putSerializable("tracksFolders", tracksFolders);
                bundle.putInt("activityFrom", Constants.FROM_FOLDERS_GRID_ACTIVITY);
                Intent intent = new Intent(FoldersGridActivity.this, LikedTracksListActivity.class);
                intent.putExtras(bundle);
                startActivity(intent);
            }
        });
    }

    /**
     * Saves tracksFolders array list to rebuild activity after rotation
     */
    @Override
    protected void onSaveInstanceState(Bundle outState) {
        outState.putSerializable("tracksFolders", tracksFolders);
        writeToSharedPreferences(this, tracksFolders);
        super.onSaveInstanceState(outState);
    }

    @Override
    public void onBackPressed() {
        super.onBackPressed();
        moveTaskToBack(true);
    }

    /**
     * After app is launched need to initialize audio player service
     */
    private void initService() {
        Intent intent = new Intent(FoldersGridActivity.this, AudioPlayerService.class);
        startService(intent);
    }

    /**
     * If tracksFolders is not stored in shared preferences, it is initialized from resources.
     * @return arrayList of folders with arrayList of tracks belonging to every folder
     */
    private ArrayList<TracksFolder> getTracksFolders() {
        Resources resources = getResources();
        TypedArray pictures = resources.obtainTypedArray(R.array.pictures);

        ArrayList<TracksFolder> tracksFolders = new ArrayList<>();
        for (int i = 0; i < foldersName.length; i++) {
            String folderName = foldersName[i];
            int imageResource = pictures.getResourceId(i, -1);
            ArrayList<Track> tracks = getArrayListOfTracks(resources, i, imageResource);
            tracksFolders.add(new TracksFolder(folderName, imageResource, tracks));
        }
        pictures.recycle();
        return tracksFolders;
    }

    /**
     * @param resources      need to get typedArray to get array of audio files names
     * @param folderPosition passed to Track constructor
     * @param imageResource  passed to Track constructor
     *                       Liked tracks are obtained from shared preferences
     * @return array list of tracks for every folder
     */
    private ArrayList<Track> getArrayListOfTracks(Resources resources, int folderPosition, int imageResource) {
        TypedArray audioTracksTypedArray = resources.obtainTypedArray(R.array.audio_tracks);
        int audioTracksId = audioTracksTypedArray.getResourceId(folderPosition, 0);
        String[] audio = resources.getStringArray(audioTracksId);
        audioTracksTypedArray.recycle();

        TypedArray trackNamesTypedArray = resources.obtainTypedArray(R.array.track_names);
        int trackNamesId = trackNamesTypedArray.getResourceId(folderPosition, 0);
        String[] trackNames = resources.getStringArray(trackNamesId);
        trackNamesTypedArray.recycle();

        SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());

        ArrayList<Track> tracksInFolder = new ArrayList<>();
         for (int i = 0; i < trackNames.length; i++) {
            int audioResource = resources.getIdentifier(audio[i], "raw", this.getPackageName());
            String trackName = trackNames[i].replace("_", " ");
            boolean isLiked = sharedPreferences.getBoolean(String.valueOf(audioResource), false);
            tracksInFolder.add(new Track(audioResource, trackName, imageResource, isLiked));
        }
        return tracksInFolder;
    }
    //todo убрать полосы в списках треков
}

Updated class:

@NonNull
    private  ArrayList<TracksFolder> getTracksFoldersAndInitService(Bundle savedInstanceState) {
        if (getIntent().getExtras() != null) { //activity is triggered via on back pressed
            Bundle bundle = getIntent().getExtras();
            tracksFolders = (ArrayList<TracksFolder>) bundle.getSerializable("tracksFolders");
        } else if (savedInstanceState != null) { //this happens after screen is rotated
            tracksFolders = (ArrayList<TracksFolder>) savedInstanceState.getSerializable("tracksFolders");
        } else { //this happens if app is launched by user
            tracksFolders = getTracksFoldersFromResources();
            initService();
        }
        return tracksFolders;
    }

@Nick Fortescue, @Ranjan, thank you both for advices, but tracksFolders is never NULL. I have edited class (you can see it below "Updated class:") and separated tracksFolders instantiation into another method with @NonNull annotation. I have updated app with this changes and later got same NPE with same log. I know it's the worst way to test app on users, but I had no other option. If you were right, log would say that Exception is thrown in getTracksFoldersAndInitService method. But it didn't. Consequently, problem is in adapter. Correct me if I'm wrong.

Answer 1

The NullPointerException occurring in GridAdapter.getCount() doesn't mean getCount() returns null. It means it is accessing a null. Since you uploaded your code (Great!) we can see there are only two possible problems:

• trackFolders is null , so when you access it you get an NPE
• trackFolders returns a null Integer, so when it gets converted to an int you get an NPE

The second option isn't possible, because .size() on an ArrayList returns an int too, so it must be the first option.

trackFolders is set in the constructor, which is set in your onCreate() method from the bundle, from the saved state, or from getTracksFolders() . It looks like getTracksFolders() can't return null, so my guess is your activity is being started with an intent with this set to null. I would double check this in your onCreate() method, and if it happens take appropriate action, maybe replace it with a new ArrayList() ?