SQLite Android java.lang.NullPointerException

Question

I made myself little app that uses SQLite but I am not able to get it working. I get java.lang.NullPointerException. Here is my LogCat:

07-02 19:18:01.584 18829 18829 E   AndroidRuntime                               FATAL EXCEPTION: main
07-02 19:18:01.584 18829 18829 E   AndroidRuntime                               java.lang.RuntimeException: Unable to start activity ComponentInfo{com.beefcodes.biblequiz/com.beefcodes.biblequiz.GameActivity}: java.lang.NullPointerException
07-02 19:18:01.584 18829 18829 E   AndroidRuntime                               at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2343)
07-02 19:18:01.584 18829 18829 E   AndroidRuntime                               at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2395)
07-02 19:18:01.584 18829 18829 E   AndroidRuntime                               at android.app.ActivityThread.access$600(ActivityThread.java:162)
07-02 19:18:01.584 18829 18829 E   AndroidRuntime                               at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1364)
07-02 19:18:01.584 18829 18829 E   AndroidRuntime                               at android.os.Handler.dispatchMessage(Handler.java:107)
07-02 19:18:01.584 18829 18829 E   AndroidRuntime                               at android.os.Looper.loop(Looper.java:194)
07-02 19:18:01.584 18829 18829 E   AndroidRuntime                               at android.app.ActivityThread.main(ActivityThread.java:5371)
07-02 19:18:01.584 18829 18829 E   AndroidRuntime                               at java.lang.reflect.Method.invokeNative(Native Method)
07-02 19:18:01.584 18829 18829 E   AndroidRuntime                               at java.lang.reflect.Method.invoke(Method.java:525)
07-02 19:18:01.584 18829 18829 E   AndroidRuntime                               at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
07-02 19:18:01.584 18829 18829 E   AndroidRuntime                               at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
07-02 19:18:01.584 18829 18829 E   AndroidRuntime                               at dalvik.system.NativeStart.main(Native Method)
07-02 19:18:01.584 18829 18829 E   AndroidRuntime                               Caused by: java.lang.NullPointerException
07-02 19:18:01.584 18829 18829 E   AndroidRuntime                               at com.beefcodes.biblequiz.MyDB.onCreate(MyDB.java:31)
07-02 19:18:01.584 18829 18829 E   AndroidRuntime                               at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:252)
07-02 19:18:01.584 18829 18829 E   AndroidRuntime                               at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:164)
07-02 19:18:01.584 18829 18829 E   AndroidRuntime                               at com.beefcodes.biblequiz.MyDB.<init>(MyDB.java:25)
07-02 19:18:01.584 18829 18829 E   AndroidRuntime                               at com.beefcodes.biblequiz.GameActivity.onCreate(GameActivity.java:22)
07-02 19:18:01.584 18829 18829 E   AndroidRuntime                               at android.app.Activity.performCreate(Activity.java:5122)
07-02 19:18:01.584 18829 18829 E   AndroidRuntime                               at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1081)
07-02 19:18:01.584 18829 18829 E   AndroidRuntime                               at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2307)
07-02 19:18:01.584 18829 18829 E   AndroidRuntime                               ... 11 more

Here is my Activity class:

package com.beefcodes.biblequiz;
import android.app.*;
import android.os.Bundle;
import java.io.*;
import javax.xml.parsers.*;
import org.w3c.dom.*;
import android.widget.*;
import android.database.*;
import com.beefcodes.biblequiz.MyDB;

public class GameActivity extends Activity {

    public static MyDB DBM;
    private Cursor cursor;
    public String current_dif = "begginer";
    public String current_right;

    @Override
    protected void onCreate(Bundle b) {
        super.onCreate(b);
        setContentView(R.layout.game);
        DBM = new MyDB(this);
        getData();
        cursor = DBM.getValuesfromDif(current_dif);
        if (DBM == null) {
            DBM = new MyDB(this);
        }
    }

    void getData () {
        InputStream stream = getResources().openRawResource(R.raw.otazky);

        try {
            DocumentBuilder builder = DocumentBuilderFactory.newInstance().newDocumentBuilder();
            Document doc = builder.parse(stream, null);
            NodeList otazky = doc.getElementsByTagName("otazka");
            for (int i = 0;i<otazky.getLength();i++) {
                String otazka = ((Element)otazky.item(i)).getAttribute("text");
                String odpA = ((Element)otazky.item(i)).getAttribute("a");
                String odpB = ((Element)otazky.item(i)).getAttribute("b");
                String odpC = ((Element)otazky.item(i)).getAttribute("c");
                String odpD = ((Element)otazky.item(i)).getAttribute("d");
                String obtiznost = ((Element)otazky.item(i)).getAttribute("obtiznost");
                String spravne = ((Element)otazky.item(i)).getAttribute("spravne");
                DBM.WriteValue(otazka, odpA, odpB, odpC, odpD, obtiznost, spravne);
            }
        } catch (Exception ex) {
            Toast.makeText(this, "Nastala chyba při načítání souboru.", Toast.LENGTH_LONG).show();
        }
    }

    void writeValues (String text, String butA, String butB, String butC, String butD) {
        TextView scoretext = (TextView)findViewById(R.id.scoretext);
        TextView otazkatext = (TextView)findViewById(R.id.gameTextView);
        Button buttA = (Button)findViewById(R.id.gameButtonA);
        Button buttB = (Button)findViewById(R.id.gameButtonB);
        Button buttC = (Button)findViewById(R.id.gameButtonC);
        Button buttD = (Button)findViewById(R.id.gameButtonD);
        otazkatext.setText(text);
        buttA.setText(butA);
        buttB.setText(butB);
        buttC.setText(butC);
        buttD.setText(butD);
    }

    public void getValueFromCursor (Cursor c) {
        if(c.moveToFirst()) {
            String otazka = c.getString(c.getColumnIndex(DBM.Q_TEXT));
            String odpA = c.getString(c.getColumnIndex(DBM.Q_A1));
            String odpB = c.getString(c.getColumnIndex(DBM.Q_A2));
            String odpC = c.getString(c.getColumnIndex(DBM.Q_A3));
            String odpD = c.getString(c.getColumnIndex(DBM.Q_A4));
            String spravne = c.getString(c.getColumnIndex(DBM.spravne));
            writeValues(otazka, odpA, odpB, odpC, odpD);
            setCurrentRight(spravne);
        }
        c.close();
    }

    public void setCurrentRight (String spravny) {
        current_right = spravny;
    }

}

Here is my SQLite class:

package com.beefcodes.biblequiz;
import android.database.sqlite.*;
import android.content.*;
import android.database.*;

public class MyDB extends SQLiteOpenHelper {

    private SQLiteDatabase db;
    private static final String DB_NAME = "dbotazky";
    private static final String TABLE_NAME = "otazky";
    private static final int DB_VERSION = 10;
    public static final String ID = "_id";
    public static final String Q_TEXT = "text";
    public static final String Q_A1 = "odpa";
    public static final String Q_A2 = "odpb";
    public static final String Q_A3 = "odpc";
    public static final String Q_A4 = "odpd";
    public static final String obtiznost = "dif";
    public static final String spravne = "true";

    private static final String DATABASE_CREATE = "CREATE TABLE " + TABLE_NAME + " ( " + ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " + Q_A1 + " TEXT, " + Q_A2 + " TEXT, " + Q_A3 + " TEXT, " + Q_A4 + " TEXT, " + obtiznost + " TEXT, " + spravne + " TEXT);";
    private static MyDB DBM = null;


    public MyDB getInstance (Context context) {
        if (DBM == null) {
            DBM = new MyDB(context.getApplicationContext());
        }
        //db = MyDB.getInstance(context).getWritableDatabase();
        return DBM;
    }

    private MyDB (Context context) {
        super(context, DB_NAME, null, DB_VERSION);
        db = MyDB.getInstance(context).getWritableDatabase();
    }

    @Override
    public void onCreate(SQLiteDatabase p1)
    {
        db.execSQL(DATABASE_CREATE);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldv, int newv)
    {
        db.execSQL("DROP TABLE IF EXIST " + TABLE_NAME);
        onCreate(db);
    }



    public void close() {
        db.close();
    }

   public void WriteValue (String otazka, String aa, String ab, String ac, String ad, String dif, String spravny) {
       ContentValues cv = new ContentValues ();
       cv.put(Q_TEXT, otazka);
       cv.put(Q_A1, aa);
       cv.put(Q_A2, ab);
       cv.put(Q_A3, ac);
       cv.put(Q_A4, ad);
       cv.put(obtiznost, dif);
       cv.put(spravne, spravny);
       db.insert(TABLE_NAME, null, cv);
   }

   public Cursor getValuesfromDif (String DIF) {
       String[] sloupce = {ID, Q_TEXT, Q_A1, Q_A2, Q_A3, Q_A4, obtiznost, spravne};
       String where = obtiznost + "=?";
       String[] params = {DIF};
       String orderby = "RANDOM()";
       String limit = "LIMIT 1";
       Cursor cursor = db.query(TABLE_NAME, sloupce, where, params, null, null, orderby, limit);
       return cursor;
   }
}

Thanks for any help.

In your `onCreate` method you should call the `MyDB`'s `getInstance` method. Don't try to use `new` because the constructor is private. — Eric Martinez, Jul 04 '15 at 15:59
In that case the singleton would lose sense and [it's a good practice](http://stackoverflow.com/questions/2493331/what-are-the-best-practices-for-sqlite-on-android/3689883#3689883) — Eric Martinez, Jul 04 '15 at 16:25
I dont know what is wrong with me but I am not able to use getInstance as function. Any idea? — Jan Polak, Jul 04 '15 at 17:53
It looks like you're trying to write `getInstance()` as a static method. That will only work if you add the `static` modifier. — Dan Getz, Jul 04 '15 at 19:28
Thanks Dan, that works but i still get error. It is from getInstance method. — Jan Polak, Jul 05 '15 at 07:55
Well, it's probably related to the fact that you're not using `SQLiteHelper` as intended. If I were you I'd reread the documentation. — Dan Getz, Jul 05 '15 at 19:33

SQLite Android java.lang.NullPointerException

0 Answers0