I will read an arraylist created from sqlite to show content in listview but I get an error message

Question

The objective is a ListView with all Games from a specific team. How you see, I created a function (getAllGamesByTeam()) in GamesFragment.java to fill a arraylist with all games. Always, when I start this Fragment, I get the error message:

FATAL EXCEPTION: main Process: vcoach.com, PID: 5881 java.lang.NullPointerException: Attempt to invoke virtual method 'void vcoach.com.SQLiteDB_statistics_tblGame_DataSource.openReadOnly()' on a null object reference at vcoach.com.GamesFragment.onResume(GamesFragment.java:84)

GamesFragment.java:84 point at line dataSource_tblGame.openReadOnly(); in Function onResume(). The last action in Run-Log of Android Studio is open the data source. I really don't know, what could it be and I am depending on your help because I investigated a lot of time to solve this problem myself but without any success.

Code

GamesFragment.java

public class GamesFragment extends Fragment{

public static ListView listView_Games;

public static final String LOG_TAG = GamesFragment.class.getSimpleName();
public static SQLiteDB_statistics_tblGame_DataSource dataSource_tblGame;
private SQLiteDatabase db_statistics;

@Nullable
@Override
public View onCreateView(LayoutInflater inflater_games, ViewGroup container, Bundle savedInstanceState) {
    View view_games = inflater_games.inflate(R.layout.fragment_games, container, false);

    //Initialize Objects
    listView_Games = (ListView) view_games.findViewById(R.id.listView_Games);
    final FloatingActionButton floatingActionButton_startagame = (FloatingActionButton) view_games.findViewById(R.id.floatingActionButton_startagame);
    final Button button_welcome = (Button) view_games.findViewById(R.id.button_welcome);

    //FloatingActionButton floatingActionBbutton_startagame
    floatingActionButton_startagame.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view){
            //Create DialogFragment
            DialogFragment newGameDialog = new NewGameDialog();
            newGameDialog.show(getActivity().getSupportFragmentManager(), "Dialog");

            //Create Bundle and transfer variable gametime to GameActivity
            Bundle toDialog_NewGameDialog = new Bundle();
            newGameDialog.setArguments(toDialog_NewGameDialog);
        }
    });

    //Button button_welcome
    button_welcome.setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {
            startActivity(new Intent(getActivity(),WelcomeActivity.class));
        }
    });

    return view_games;
}

public void getAllGamesByTeam(){
    GamesFragment_ListView_Games.arrayList_Games = dataSource_tblGame.getAllGamesByTeam(1);

    GamesFragment_ListView_Games.Adapter_ListView_games adapter_ListView_games = new GamesFragment_ListView_Games.Adapter_ListView_games(getActivity(), GamesFragment_ListView_Games.arrayList_Games);
    listView_Games.setAdapter(adapter_ListView_games);
    listView_Games.setChoiceMode(AbsListView.CHOICE_MODE_MULTIPLE);
}

@Override
public void onResume() {
    super.onResume();

    Log.d(LOG_TAG, "Die Datenquelle wird geöffnet.");
    dataSource_tblGame.openReadOnly();

    getAllGamesByTeam();
}

@Override
public void onPause() {
    super.onPause();

    Log.d(LOG_TAG, "Die Datenquelle wird geschlossen.");
    dataSource_tblGame.close();
}

SQLiteDB_statistics_tblGame_DataSource.java

public class SQLiteDB_statistics_tblGame_DataSource {

private static final String LOG_TAG = SQLiteDB_statistics_Helper.class.getSimpleName();

private SQLiteDatabase db_statistics;
private SQLiteDB_statistics_Helper db_statistics_helper;

private String[] table_game_columns = {
        SQLiteDB_statistics_Helper.TABLE_GAME_COLUMN_ID,
        SQLiteDB_statistics_Helper.TABLE_GAME_COLUMN_HOMETEAM_ID,
        SQLiteDB_statistics_Helper.TABLE_GAME_COLUMN_GUESTTEAM,
        SQLiteDB_statistics_Helper.TABLE_GAME_COLUMN_DATE
};

public SQLiteDB_statistics_tblGame_DataSource(Context context){
    Log.d(LOG_TAG, "Unsere DataSource erzeugt jetzt den db_statistics_helper.");
    db_statistics_helper = new SQLiteDB_statistics_Helper(context);
}

public void open(){
    Log.d(LOG_TAG, "Unsere DataSource erzeugt jetzt den SQLiteDB_statistics_Helper.");
    db_statistics = db_statistics_helper.getWritableDatabase();
    Log.d(LOG_TAG, "Datenbank-Referenz erhalten. Pfad zur Datenbank: " + db_statistics.getPath());
}

public void openReadOnly(){
    Log.d(LOG_TAG, "Unsere DataSource erzeugt jetzt den SQLiteDB_statistics_Helper aber nur zum Lesen.");
    db_statistics = db_statistics_helper.getReadableDatabase();
    Log.d(LOG_TAG, "Datenbank-Referenz erhalten. Pfad zur Datenbank: " + db_statistics.getPath());
}

public void close(){
    db_statistics_helper.close();
    Log.d(LOG_TAG, "Datenbank mit Hilfe des SQLiteDB_statistics_Helpers geschlossen.");
}

//save a game in Table Game
public SQLiteDB_statistics_tblGame createGame_SQLiteDB_statistics(long hometeam_id, String guestteam, String date){
    open();

    ContentValues values_game = new ContentValues();
    values_game.put(SQLiteDB_statistics_Helper.TABLE_GAME_COLUMN_HOMETEAM_ID, hometeam_id);
    values_game.put(SQLiteDB_statistics_Helper.TABLE_GAME_COLUMN_GUESTTEAM, guestteam);
    values_game.put(SQLiteDB_statistics_Helper.TABLE_GAME_COLUMN_DATE, date);

    long insertId = db_statistics.insert(SQLiteDB_statistics_Helper.TABLE_GAME, null, values_game);

    Cursor cursor = db_statistics.query(SQLiteDB_statistics_Helper.TABLE_GAME, table_game_columns, SQLiteDB_statistics_Helper.TABLE_GAME_COLUMN_ID + "=" + insertId, null, null, null, null);

    cursor.moveToFirst();
    SQLiteDB_statistics_tblGame sqLiteDB_statistics_tblGame = cursorGame_ToSQLite_statistics(cursor);
    cursor.close();

    return sqLiteDB_statistics_tblGame;
}

public SQLiteDB_statistics_tblGame cursorGame_ToSQLite_statistics(Cursor cursor){

    int idIndex = cursor.getColumnIndex(SQLiteDB_statistics_Helper.TABLE_GAME_COLUMN_ID);
    int idHometeam_id = cursor.getColumnIndex(SQLiteDB_statistics_Helper.TABLE_GAME_COLUMN_HOMETEAM_ID);
    int idGuestteam = cursor.getColumnIndex(SQLiteDB_statistics_Helper.TABLE_GAME_COLUMN_GUESTTEAM);
    int idDate = cursor.getColumnIndex(SQLiteDB_statistics_Helper.TABLE_GAME_COLUMN_DATE);

    long id = cursor.getLong(idIndex);
    long hometeam_id = cursor.getLong(idHometeam_id);
    String guestteam = cursor.getString(idGuestteam);
    String date = cursor.getString(idDate);

    SQLiteDB_statistics_tblGame sqLiteDB_statistics_tblGame = new SQLiteDB_statistics_tblGame(id, hometeam_id, guestteam, date);

    return sqLiteDB_statistics_tblGame;
}


/*<!-- Experimental -->*/

public ArrayList<SQLiteDB_statistics_tblGame> getAllGamesByTeam(int hometeam_id) {
    ArrayList<SQLiteDB_statistics_tblGame> arrayList_Games = new ArrayList<SQLiteDB_statistics_tblGame>();

    String selectQuery = "SELECT * FROM " + db_statistics_helper.TABLE_GAME
            + " WHERE " + db_statistics_helper.TABLE_GAME + "." + db_statistics_helper.TABLE_GAME_COLUMN_HOMETEAM_ID + " = " + hometeam_id;
    Log.e(LOG_TAG, selectQuery);

    Cursor cursor = db_statistics.rawQuery(selectQuery, null);

    if(cursor.moveToFirst()){
        do{
            SQLiteDB_statistics_tblGame sqLiteDB_statistics_tblGame = new SQLiteDB_statistics_tblGame();
            sqLiteDB_statistics_tblGame.setGame_id(cursor.getInt(cursor.getColumnIndex(db_statistics_helper.TABLE_GAME_COLUMN_ID)));
            sqLiteDB_statistics_tblGame.setHometeam_idfs(cursor.getInt(cursor.getColumnIndex(db_statistics_helper.TABLE_GAME_COLUMN_HOMETEAM_ID)));
            sqLiteDB_statistics_tblGame.setGuestteam(cursor.getString(cursor.getColumnIndex(db_statistics_helper.TABLE_GAME_COLUMN_GUESTTEAM)));
            sqLiteDB_statistics_tblGame.setDate(cursor.getString(cursor.getColumnIndex(db_statistics_helper.TABLE_GAME_COLUMN_DATE)));

            arrayList_Games.add(sqLiteDB_statistics_tblGame);

        }while (cursor.moveToNext());
    }
    return arrayList_Games;
}

SQLiteDB_statistics_tblGame.java

public class SQLiteDB_statistics_tblGame {

public long game_id;
public long hometeam_idfs;
public String guestteam;
public String date;

public SQLiteDB_statistics_tblGame(){
}

public SQLiteDB_statistics_tblGame(long game_id, long hometeam_idfs, String guestteam, String date){
    this.game_id = game_id;
    this.hometeam_idfs = hometeam_idfs;
    this.guestteam = guestteam;
    this.date = date;
}

public long getGame_id() {
    return game_id;
}

public void setGame_id(long game_id){
    this.game_id = game_id;
}

public long getHometeam_idfs() {
    return hometeam_idfs;
}

public void setHometeam_idfs(long hometeam_idfs){
    this.hometeam_idfs = hometeam_idfs;
}

public String getGuestteam() {
    return guestteam;
}

public void setGuestteam(String guestteam){
    this.guestteam = guestteam;
}

public String getDate() {
    return date;
}

public void setDate(String date){
    this.date = date;
}

}

i think you need to call `SQLiteDB_statistics_tblGame_DataSource()` first before opening the db with `dataSource_tblGame.openReadOnly();` — ישו אוהב אותך, Feb 09 '17 at 19:52
Btw, you need to stick with the code style convention for class and method name. Don't use underscore. For class name, start with Uppercase, something like `public class YourClassName {...}`. And for method, start with lower case, something like `private void yourMethodName() {...}` — ישו אוהב אותך, Feb 09 '17 at 19:55

ישו אוהב אותך · Answer 1 · 2017-02-10T23:39:50.910

0

you need to call SQLiteDB_statistics_tblGame_DataSource() first to initialize your SQLiteDB_statistics_tblGame_DataSource object. Then you can open the db with dataSource_tblGame.openReadOnly();

Btw, you need to stick with the Java code style convention for class and method name.

Don't use underscore for class and method name.
For class name, start with Uppercase, something like public class YourClassName {...}.
And for method, start with lowercase, something like private void yourMethodName() {...}

UPDATE
Don't use static variable. Just use:

SQLiteDB_statistics_tblGame_DataSource dataSource_tblGame;

to declare the variable. Then before accessing the db, initialize it with

dataSource_tblGame = new SQLiteDB_statistics_tblGame_DataSource(this);

edited Feb 10 '17 at 23:39

answered Feb 09 '17 at 20:05

ישו אוהב אותך

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Thanks for your answer. I will optimize Java code style convention ;). – SmnHgr Feb 10 '17 at 07:50
Now to the problem. I defined `SQLiteDB_statistics_tblGame_DataSource()` in the top of `public class GamesFragment` as `public static SQLiteDB_statistics_tblGame_DataSource dataSource_tblGame;` Is that not enough to reference with `dataSource_tblGame` in front of `openReadOnly()`? – SmnHgr Feb 10 '17 at 07:57
Don't use static variable. Just use `SQLiteDB_statistics_tblGame_DataSource dataSource_tblGame;` to declare the variable. Then before accessing the db, initialize it with `dataSource_tblGame = new SQLiteDB_statistics_tblGame_DataSource(this);` – ישו אוהב אותך Feb 10 '17 at 08:02
It works. Thanks a lot for your fast help. You can't imagine how happy I am! :) – SmnHgr Feb 10 '17 at 21:21
You're very welcome. I'm glad that I can help you. I'll integrate the the comment. You can accept the answer then. – ישו אוהב אותך Feb 10 '17 at 23:38

I will read an arraylist created from sqlite to show content in listview but I get an error message

Code

1 Answers1