Attempt to invoke interface method 'int android.database.Cursor.getCount()' on a null object reference

Question

I do have a problem that gives me a headache. I store some images of my city in the sqlite database via a custom content provider. However when I run my app I get a null cursor.

Caused by: java.lang.NullPointerException: Attempt to invoke interface method 'int android.database.Cursor.getCount()' on a null object reference
                                                 at theo.testing.androidcustomloaders.fragments.MainActivityFragment.onActivityCreated(MainActivityFragment.java:74)
                                                 at android.support.v4.app.Fragment.performActivityCreated(Fragment.java:2089)
                                                 at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1133)
                                                 at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1290)
                                                 at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:801)
                                                 at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1677)
                                                 at android.support.v4.app.FragmentController.execPendingActions(FragmentController.java:388)
                                                 at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:604)
                                                 at android.support.v7.app.AppCompatActivity.onStart(AppCompatActivity.java:178)
                                                 at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1220)
                                                 at android.app.Activity.performStart(Activity.java:5992)
                                                 at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2261)
                                                 at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2358) 
                                                 at android.app.ActivityThread.access$800(ActivityThread.java:144) 
                                                 at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278) 
                                                 at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                 at android.os.Looper.loop(Looper.java:135) 
                                                 at android.app.ActivityThread.main(ActivityThread.java:5219) 
                                                 at java.lang.reflect.Method.invoke(Native Method) 
                                                 at java.lang.reflect.Method.invoke(Method.java:372) 
                                                 at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:898) 
                                                 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:693)

That would mean the the info are not stored correctly or the Uri of my provider is somehow faulty. So.

MyCityContract

public class MyCityContract {

public static final String CONTENT_AUTHORITY = "theo.testing.customloaders";

public static final Uri BASE_CONTENT_URI = Uri.parse("content://" + CONTENT_AUTHORITY);

public static final class MyCityEntry implements BaseColumns{
    //table name
    public static final String TABLE_MY_CITY = "my_city";
    //columns
    public static final String _ID = "_id";
    public static final String COLUMN_NAME = "name";
    public static final String COLUMN_ICON = "icon";

    // create content uri
    public static final Uri CONTENT_URI = BASE_CONTENT_URI.buildUpon()
            .appendPath(TABLE_MY_CITY).build();
    // create cursor of base type directory for multiple entries
    public static final String CONTENT_DIR_TYPE =
            ContentResolver.CURSOR_DIR_BASE_TYPE + "/" + CONTENT_AUTHORITY + "/" + TABLE_MY_CITY;
    // create cursor of base type item for single entry
    public static final String CONTENT_ITEM_TYPE =
            ContentResolver.CURSOR_ITEM_BASE_TYPE +"/" + CONTENT_AUTHORITY + "/" + TABLE_MY_CITY;

    // for building URIs on insertion
    public static Uri buildFlavorsUri(long id){
        return ContentUris.withAppendedId(CONTENT_URI, id);
    }

  }
}

MyCityDbHelper

public class MyCityDbHelper  extends SQLiteOpenHelper{
public static final String LOG_TAG = MyCityDbHelper.class.getSimpleName();
//name & version
public static final String DATABASE_NAME = "city.db";
public static final int DATABASE_VERSION = 4;
// Create the database
public MyCityDbHelper(Context context) {
    super(context, DATABASE_NAME,null,DATABASE_VERSION);
}

@Override
public void onCreate(SQLiteDatabase sqLiteDatabase) {
    final String SQL_CREATE_MY_CITY_TABLE = "CREATE TABLE " +
            MyCityContract.MyCityEntry.TABLE_MY_CITY + "(" + MyCityContract.MyCityEntry._ID +
            " INTEGER PRIMARY KEY AUTOINCREMENT, " +
            MyCityContract.MyCityEntry.COLUMN_NAME + " TEXT NOT NULL, " +
            MyCityContract.MyCityEntry.COLUMN_ICON + " INTEGER NOT NULL);";


    sqLiteDatabase.execSQL(SQL_CREATE_MY_CITY_TABLE);
}

@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int oldVersion, int newVersion) {
    Log.w(LOG_TAG, "Upgrading database from version " + oldVersion + " to " +
            newVersion + ". OLD DATA WILL BE DESTROYED");
    // Drop the table
    sqLiteDatabase.execSQL("DROP TABLE IF EXISTS " + MyCityContract.MyCityEntry.TABLE_MY_CITY);
    sqLiteDatabase.execSQL("DELETE FROM SQLITE_SEQUENCE WHERE NAME = '" +
            MyCityContract.MyCityEntry.TABLE_MY_CITY + "'");

    // re-create database
    onCreate(sqLiteDatabase);
   }
}

MyCityProvider

public class MyCityProvider extends ContentProvider {
private static final String LOG_TAG = MyCityProvider.class.getSimpleName();
private static final UriMatcher sUriMatcher = buildUriMatcher();
private MyCityDbHelper myCityDbHelper;

//Codes for UriMatcher
private static final int MY_CITY = 100;
private static final int MY_CITY_WITH_ID = 200;


private static UriMatcher buildUriMatcher(){
    // Build a UriMatcher by adding a specific code to return based on a match
    // It's common to use NO_MATCH as the code for this case.
    final UriMatcher matcher = new UriMatcher(UriMatcher.NO_MATCH);
    final String authority = MyCityContract.CONTENT_AUTHORITY;

    //add code for each URI


 matcher.addURI(authority,MyCityContract.MyCityEntry.TABLE_MY_CITY,MY_CITY);
    matcher.addURI(authority,MyCityContract.MyCityEntry.TABLE_MY_CITY + "/#",MY_CITY_WITH_ID);

    return matcher;

}
@Override
public boolean onCreate() {
    myCityDbHelper = new MyCityDbHelper(getContext());

    return true;
}

@Override
public String getType(Uri uri) {
    final int match = sUriMatcher.match(uri);

    switch (match){
        case MY_CITY: {
            return MyCityContract.MyCityEntry.CONTENT_DIR_TYPE;
        }
        case MY_CITY_WITH_ID:{
            return MyCityContract.MyCityEntry.CONTENT_ITEM_TYPE;

        }
        default:{
            throw new UnsupportedOperationException("Unknown uri: " + uri);
        }
    }
}
@Override
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder){
    Cursor retCursor;
    switch(sUriMatcher.match(uri)){
        // All Flavors selected
        case MY_CITY:{
            retCursor = myCityDbHelper.getReadableDatabase().query(
                    MyCityContract.MyCityEntry.TABLE_MY_CITY,
                    projection,
                    selection,
                    selectionArgs,
                    null,
                    null,
                    sortOrder);
            return retCursor;
        }
        // Individual flavor based on Id selected
        case MY_CITY_WITH_ID:{
            retCursor = myCityDbHelper.getReadableDatabase().query(
                    MyCityContract.MyCityEntry.TABLE_MY_CITY,
                    projection,
                    MyCityContract.MyCityEntry._ID + " = ?",
                    new String[] {String.valueOf(ContentUris.parseId(uri))},
                    null,
                    null,
                    sortOrder);
            return retCursor;
        }
        default:{
            // By default, we assume a bad URI
            throw new UnsupportedOperationException("Unknown uri: " + uri);
        }
    }
}




@Override
public Uri insert(Uri uri, ContentValues contentValues) {
    final SQLiteDatabase db = myCityDbHelper.getWritableDatabase();

    Uri returnUri;

    switch (sUriMatcher.match(uri)){
        case MY_CITY:

            long _id = db.insert(MyCityContract.MyCityEntry.TABLE_MY_CITY,null,contentValues);
            Log.d("id",String.valueOf(_id));
            // insert unless it is already contained in the database
            if(_id>0){
                returnUri = MyCityContract.MyCityEntry.buildFlavorsUri(_id);
            }else {
                throw new android.database.SQLException("Failed to insert row into: " + uri);
            }
            break;
        default: {
            throw  new UnsupportedOperationException("Unknown uri: " + uri );
        }
    }

    getContext().getContentResolver().notifyChange(uri,null);
    return returnUri;
}

@Override
public int delete(Uri uri, String selection, String[] selectionArgs) {
    final SQLiteDatabase db = myCityDbHelper.getWritableDatabase();
    final int match = sUriMatcher.match(uri);
    int numDeleted;
    switch(match){
        case MY_CITY:
            numDeleted = db.delete(
                    MyCityContract.MyCityEntry.TABLE_MY_CITY, selection, selectionArgs);
            // reset _ID
            db.execSQL("DELETE FROM SQLITE_SEQUENCE WHERE NAME = '" +
                    MyCityContract.MyCityEntry.TABLE_MY_CITY + "'");
            break;
        case MY_CITY_WITH_ID:
            numDeleted = db.delete(MyCityContract.MyCityEntry.TABLE_MY_CITY,
                    MyCityContract.MyCityEntry._ID + " = ?",
                    new String[]{String.valueOf(ContentUris.parseId(uri))});
            // reset _ID
            db.execSQL("DELETE FROM SQLITE_SEQUENCE WHERE NAME = '" +
                    MyCityContract.MyCityEntry.TABLE_MY_CITY  + "'");

            break;
        default:
            throw new UnsupportedOperationException("Unknown uri: " + uri);
    }

    return numDeleted;
}
@Override
public int bulkInsert(Uri uri, ContentValues[] values){
    final SQLiteDatabase db = myCityDbHelper.getWritableDatabase();
    final int match = sUriMatcher.match(uri);
    switch(match){
        case MY_CITY:
            // allows for multiple transactions
            db.beginTransaction();

            // keep track of successful inserts
            int numInserted = 0;
            try{
                for(ContentValues value : values){
                    if (value == null){
                        throw new IllegalArgumentException("Cannot have null content values");
                    }
                    long _id = -1;
                    try{
                        _id = db.insertOrThrow(MyCityContract.MyCityEntry.TABLE_MY_CITY,
                                null, value);
                    }catch(SQLiteConstraintException e) {
                        Log.w(LOG_TAG, "Attempting to insert " +
                                value.getAsString(
                                        MyCityContract.MyCityEntry.COLUMN_NAME)
                                + " but value is already in database.");
                    }
                    if (_id != -1){
                        numInserted++;
                    }
                }
                if(numInserted > 0){
                    // If no errors, declare a successful transaction.
                    // database will not populate if this is not called
                    db.setTransactionSuccessful();
                }
            } finally {
                // all transactions occur at once
                db.endTransaction();
            }
            if (numInserted > 0){
                // if there was successful insertion, notify the content resolver that there
                // was a change
                getContext().getContentResolver().notifyChange(uri, null);
            }
            return numInserted;
        default:
            return super.bulkInsert(uri, values);
    }
}
@Override
public int update(Uri uri, ContentValues contentValues, String selection, String[] selectionArgs){
    final SQLiteDatabase db = myCityDbHelper.getWritableDatabase();
    int numUpdated = 0;

    if (contentValues == null){
        throw new IllegalArgumentException("Cannot have null content values");
    }

    switch(sUriMatcher.match(uri)){
        case MY_CITY:{
            numUpdated = db.update(MyCityContract.MyCityEntry.TABLE_MY_CITY,
                    contentValues,
                    selection,
                    selectionArgs);
            break;
        }
        case MY_CITY_WITH_ID: {
            numUpdated = db.update(MyCityContract.MyCityEntry.TABLE_MY_CITY,
                    contentValues,
                    MyCityContract.MyCityEntry._ID + " = ?",
                    new String[] {String.valueOf(ContentUris.parseId(uri))});
            break;
        }
        default:{
            throw new UnsupportedOperationException("Unknown uri: " + uri);
        }
    }

    if (numUpdated > 0){
        getContext().getContentResolver().notifyChange(uri, null);
    }

    return numUpdated;
  }
}

MainActivityFragment

public class MainActivityFragment extends Fragment implements LoaderManager.LoaderCallbacks<Cursor>{
private static final String LOG_TAG = MainActivityFragment.class.getSimpleName();
private MyCityAdpapter myCityAdpapter;
private static final int CURSOR_LOADER_ID = 0;
private GridView mGridView;


MyCity[] mMyCity = {
        new MyCity("Ancient Theatre - Larisa", R.drawable.larissa1),

        new MyCity("Ancient Theatre - Larisa", R.drawable.larissa2),
        new MyCity("Municipality park", R.drawable.larissa3),
        new MyCity("Municipality park", R.drawable.larissa4),
        new MyCity("Old trains",R.drawable.larissa5),
        new MyCity("Old trains",R.drawable.larissa6),
        new MyCity("Church",
                R.drawable.larissa7),
        new MyCity("Church",
                R.drawable.larissa8),
        new MyCity("Alcazar park",
                R.drawable.larissa9),
        new MyCity("Alcazar park",
                R.drawable.larissa10),
        new MyCity("AEL FC Arena",
                R.drawable.larissa11),
        new MyCity("AEL FC Arena",
                R.drawable.larissa12),
        new MyCity("Larissa Fair",
                R.drawable.larissa13),
        new MyCity("Larissa Fair",
                R.drawable.larissa14),
        new MyCity("Larissa Fair",
                R.drawable.larissa15),
        new MyCity("Larissa Fair",
                R.drawable.larissa16)

};
public MainActivityFragment() {
    // Required empty public constructor
}

@Override
public void onActivityCreated(@Nullable Bundle savedInstanceState) {
    Cursor c =
            getActivity().getContentResolver().query(MyCityContract.MyCityEntry.CONTENT_URI,
                    new String[]{MyCityContract.MyCityEntry._ID},
                    null,
                    null,
                    null);
    if (c.getCount() == 0){
        insertData();
    }
    // initialize loader
    getLoaderManager().initLoader(CURSOR_LOADER_ID, null, this);
    super.onActivityCreated(savedInstanceState);
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    // inflate fragment_main layout
    final View rootView = inflater.inflate(R.layout.fragment_main_activity, container, false);


    // initialize our FlavorAdapter
    myCityAdpapter = new MyCityAdpapter(getActivity(), null, 0, CURSOR_LOADER_ID);
    // initialize mGridView to the GridView in fragment_main.xml
    mGridView = (GridView) rootView.findViewById(R.id.flavors_grid);
    // set mGridView adapter to our CursorAdapter
    mGridView.setAdapter(myCityAdpapter);

    return rootView;

}

// insert data into database
public void insertData(){
    ContentValues[] cityValuesArr = new ContentValues[mMyCity.length];
    // Loop through static array of MyCity, add each to an instance of ContentValues
    // in the array of ContentValues
    for(int i = 0; i < mMyCity.length; i++){
        cityValuesArr[i] = new ContentValues();
        cityValuesArr[i].put(MyCityContract.MyCityEntry.COLUMN_ICON, mMyCity[i].image);
        cityValuesArr[i].put(MyCityContract.MyCityEntry.COLUMN_NAME,
                mMyCity[i].name);

    }

    // bulkInsert our ContentValues array
    getActivity().getContentResolver().bulkInsert(MyCityContract.MyCityEntry.CONTENT_URI,
            cityValuesArr);
}

@Override
public Loader<Cursor> onCreateLoader(int id, Bundle args){
    return new CursorLoader(getActivity(),
            MyCityContract.MyCityEntry.CONTENT_URI,
            null,
            null,
            null,
            null);
}

@Override
public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
    myCityAdpapter.swapCursor(data);
}

@Override
public void onLoaderReset(Loader<Cursor> loader){
    myCityAdpapter.swapCursor(null);
  }
}

I read the Cursor inside the onCreateView(...) method of my Fragment

@Override
public void onActivityCreated(@Nullable Bundle savedInstanceState) {
    Cursor c =
            getActivity().getContentResolver().query(MyCityContract.MyCityEntry.CONTENT_URI,
                    new String[]{MyCityContract.MyCityEntry._ID},
                    null,
                    null,
                    null);
    if (c.getCount() == 0){
        insertData();
    }
    // initialize loader
    getLoaderManager().initLoader(CURSOR_LOADER_ID, null, this);
    super.onActivityCreated(savedInstanceState);
}

and this is where I am thrown the null Cursor exception.

Any ideas?

Thanks,

Theo.

EDIT

I changed this if condition from

 if (c.getCount() == 0){
        insertData();
    }

to

  if (c == null){
        insertData();
    }

and I am getting this exception!

 Caused by: java.lang.IllegalArgumentException: Unknown URL content://theo.testing.customloaders/my_city

So there is be an error with provider. hmm...

What if you move your logic on `onActivityCreated` to `onViewCreated`? May be possible that content resolver is not available yet — Claudio Redi, Oct 10 '16 at 17:09
have you use at time of init of cursor cursor.moveToFirst()?? — Vij, Oct 10 '16 at 17:13
With cursor!=null the app doesn't crash but I don't see any images on my gridview. — Theo, Oct 10 '16 at 17:17
*a subclass of ContentProvider must be defined in the manifest file for its application, using the element* -- Have you done that? — OneCricketeer, Oct 10 '16 at 17:23

score 1 · Answer 1 · edited May 23 '17 at 12:33

1

I think you has a problem at using getActivity in onActivityCreated in your MainActivity Fragment getActivity "might" return null if called from within onActivityCreated...especially during a configuration change like orientation change because the activity gets destroyed... move that initialization to onAttach... following link helped me to find out getActivity return null in fragment onActivityCreated in some rooted device

edited May 23 '17 at 12:33

Community

1
1

answered Oct 10 '16 at 17:18

Miral Bhalani

274
2
9

Nope. Still nothing. – Theo Oct 10 '16 at 17:22
does your debug pointer goes inside MY_CITY or MY_CITY_WITH_ID Case in query ? – Miral Bhalani Oct 10 '16 at 17:32

score 1 · Answer 2 · answered Oct 10 '16 at 17:31

1

Ok. I fixed it. All I did was changing my authority name from

theo.testing.customloaders

to

theo.testing.customloaders.app

answered Oct 10 '16 at 17:31

Theo

3,099
12
53
94

Attempt to invoke interface method 'int android.database.Cursor.getCount()' on a null object reference

2 Answers2

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