NullpointerException when trying to create SQL Database

Question

My App shoult load entries from a Sql Database in a list, but when i execute it i just get a NullPointerException:

01-16 18:35:30.239: E/AndroidRuntime(2254): FATAL EXCEPTION: main
01-16 18:35:30.239: E/AndroidRuntime(2254): Process: com.mobilecartography.tudresdenspeechorganiser, PID: 2254
01-16 18:35:30.239: E/AndroidRuntime(2254): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.mobilecartography.tudresdenspeechorganiser/com.mobilecartography.tudresdenspeechorganiser.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.mobilecartography.tudresdenspeechorganiser.DatabaseHelper.createDataBase()' on a null object reference
01-16 18:35:30.239: E/AndroidRuntime(2254):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
01-16 18:35:30.239: E/AndroidRuntime(2254):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
01-16 18:35:30.239: E/AndroidRuntime(2254):     at android.app.ActivityThread.access$800(ActivityThread.java:144)
01-16 18:35:30.239: E/AndroidRuntime(2254):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
01-16 18:35:30.239: E/AndroidRuntime(2254):     at android.os.Handler.dispatchMessage(Handler.java:102)
01-16 18:35:30.239: E/AndroidRuntime(2254):     at android.os.Looper.loop(Looper.java:135)
01-16 18:35:30.239: E/AndroidRuntime(2254):     at android.app.ActivityThread.main(ActivityThread.java:5221)
01-16 18:35:30.239: E/AndroidRuntime(2254):     at java.lang.reflect.Method.invoke(Native Method)
01-16 18:35:30.239: E/AndroidRuntime(2254):     at java.lang.reflect.Method.invoke(Method.java:372)
01-16 18:35:30.239: E/AndroidRuntime(2254):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
01-16 18:35:30.239: E/AndroidRuntime(2254):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
01-16 18:35:30.239: E/AndroidRuntime(2254): Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.mobilecartography.tudresdenspeechorganiser.DatabaseHelper.createDataBase()' on a null object reference
01-16 18:35:30.239: E/AndroidRuntime(2254):     at com.mobilecartography.tudresdenspeechorganiser.CurrentDay.loadPresentations(CurrentDay.java:39)
01-16 18:35:30.239: E/AndroidRuntime(2254):     at com.mobilecartography.tudresdenspeechorganiser.MainActivity.setCurrentWeek(MainActivity.java:70)
01-16 18:35:30.239: E/AndroidRuntime(2254):     at com.mobilecartography.tudresdenspeechorganiser.MainActivity.onCreate(MainActivity.java:32)
01-16 18:35:30.239: E/AndroidRuntime(2254):     at android.app.Activity.performCreate(Activity.java:5933)
01-16 18:35:30.239: E/AndroidRuntime(2254):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
01-16 18:35:30.239: E/AndroidRuntime(2254):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
01-16 18:35:30.239: E/AndroidRuntime(2254):     ... 10 more

So the logcat and the Debugger tells me that it throws the exception when using the method createDatabase() from my dbHelper class. This method is called by loadPresentations() in CurrentDay (although my db file currently just contains dummy data). This helper class works fine on another app with the same .db file, so i´d have thought that the error is somewhere else.

Anyway here is my dbHelper Class (the .db file is stored in the project under assets/databases/):

package com.mobilecartography.tudresdenspeechorganiser;

import android.content.Context;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import com.readystatesoftware.sqliteasset.SQLiteAssetHelper;

public class DatabaseHelper extends SQLiteAssetHelper {
    private static String DB_PATH;
    private static String DB_PATH_PREFIX = "/data/data/";
    private static String DB_PATH_SUFFIX = "/databases/";
    private static String DB_NAME = "exercise_database.db";
    private SQLiteDatabase myDataBase;
    private final Context myContext;

    public DatabaseHelper(Context context) {
        super(context, DB_NAME, null, 1);
        this.myContext = context;
    }

    public void createDataBase() throws IOException {
        DB_PATH = DB_PATH_PREFIX + myContext.getPackageName() + DB_PATH_SUFFIX
                + DB_NAME;
        boolean dbExist = checkDataBase();
        SQLiteDatabase db_Read = null;
        if (dbExist) {
        } else {
            db_Read = this.getReadableDatabase();
            db_Read.close();
        }
    }

    private boolean checkDataBase() {
        SQLiteDatabase checkDB = null;
        try {
            checkDB = SQLiteDatabase.openDatabase(DB_PATH, null,
                    SQLiteDatabase.NO_LOCALIZED_COLLATORS);
            checkDB.close();
            return true;
        } catch (SQLiteException e) {
            return false;
        }
    }

    private void copyDataBase() throws IOException {
        InputStream assetsDB = myContext.getAssets().open(DB_NAME);
        File directory = new File(DB_PATH);
        if (directory.exists() == false) {
            directory.mkdir();
        }
        OutputStream dbOut = new FileOutputStream(DB_PATH);
        byte[] buffer = new byte[1024];
        int length;
        while ((length = assetsDB.read(buffer)) > 0) {
            dbOut.write(buffer, 0, length);
        }
        dbOut.flush();
        dbOut.close();
    }

    public void openDataBase() throws SQLException {
        myDataBase = SQLiteDatabase.openDatabase(DB_PATH, null,
                SQLiteDatabase.NO_LOCALIZED_COLLATORS);
    }

    public SQLiteDatabase getDataBase() throws SQLException {
        myDataBase = SQLiteDatabase.openDatabase(DB_PATH, null,
                SQLiteDatabase.NO_LOCALIZED_COLLATORS);
        return myDataBase;
    }

    @Override
    public synchronized void close() {
        if (myDataBase != null) {
            myDataBase.close();
        }
        super.close();
    }

    //@Override
    //public void onCreate(SQLiteDatabase db) {
    //}

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    }
}

Main activity:

package com.mobilecartography.tudresdenspeechorganiser;

import java.util.ArrayList;
import java.util.Calendar;
import java.util.GregorianCalendar;
import java.util.List;

import android.app.Activity;
import android.app.ListActivity;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.widget.ExpandableListView;

import com.mobilecartography.tudresdenspeechorganiser.R;
import com.mobilecartography.tudresdenspeechorganiser.DatabaseHelper;


public class MainActivity extends ListActivity {
  ArrayList<CurrentDay> currentweek = new ArrayList<CurrentDay>();

  SQLiteDatabase database = null;
    Cursor dbCursor;
    DatabaseHelper dbHelper;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    this.dbHelper = new DatabaseHelper(this);
    setCurrentWeek();
    ExpandableListView listView = (ExpandableListView) findViewById(R.id.listView);
    MyExpandableListAdapter adapter = new MyExpandableListAdapter(this,
        currentweek);
    listView.setAdapter(adapter);
  }



//fill list with 7 entrys with dates for the next 7 days, for 
//each days query presentations for that specific day from sql database
  public void setCurrentWeek() {
      Calendar cal = new GregorianCalendar();
      CurrentDay day = null;
      int numDays = cal.getActualMaximum(Calendar.DAY_OF_MONTH);
      int today = cal.get(Calendar.DAY_OF_MONTH);
      int currentmonth = cal.get(Calendar.MONTH)+1;
      int currentyear = cal.get(Calendar.YEAR);

      for (int i = 0; i < 7; i++){
            if (today+i > numDays){

            for (int h = 0; h < 7 - i; h++){

                day = new CurrentDay(1+h, currentmonth+1, currentyear);

                }
            }

        else {
                day = new CurrentDay(today+i, currentmonth, currentyear);

            }

        day.loadPresentations();
        currentweek.add(day); 
      }
 }
}

Day Object class:

    package com.mobilecartography.tudresdenspeechorganiser;

import java.io.IOException;
import java.sql.Date;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.List;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.text.format.DateFormat;
import android.widget.ArrayAdapter;

import com.mobilecartography.tudresdenspeechorganiser.DatabaseHelper;

public class CurrentDay {

    public int day;
    public int month;
    public int year;
    DatabaseHelper dbHelper;
    public List<String> children;
    SQLiteDatabase database = null;
    Cursor dbCursor;


    public CurrentDay(int day, int month, int year) {
        this.day = day;
        this.month = month;
        this.year = year;
    }


    public void loadPresentations() {

            try {
                dbHelper.createDataBase();
            } catch (IOException ioe) {
        }
        try {

        children = new ArrayList<String>();java.sql.Date(parsedUtilDate.getTime());  

            database = dbHelper.getDataBase();
            dbCursor = database.rawQuery("SELECT university FROM pres_table",
                    null);

            dbCursor.moveToFirst();
            int index = dbCursor.getColumnIndex("title");
            while (!dbCursor.isAfterLast()) {
                String record = dbCursor.getString(index);
                children.add(record);
                dbCursor.moveToNext();
            }

        } 
        finally {
            if (database != null) {
                dbHelper.close();
            }


        }
    }
}

I´ve been trying to get behind that problem all day. Does anybody see a solution?

possible duplicate of [What is a Null Pointer Exception, and how do I fix it?](http://stackoverflow.com/questions/218384/what-is-a-null-pointer-exception-and-how-do-i-fix-it) — njzk2, Jan 16 '15 at 19:37

score 0 · Answer 1 · answered Jan 16 '15 at 19:22

0

You never initialize dbHelper in CurrentDay. So dbHelper.createDataBase(); cases the NPE.

answered Jan 16 '15 at 19:22

Jens

67,715
15
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113

score 0 · Accepted Answer · answered Jan 16 '15 at 19:23

0

You have 2 dbHelper objects. 1 in MainActivity which is set properly. And another 1 in CurrentDay which throws your error.

Try this:

day.dbHelper = dbHelper;
day.loadPresentations();

answered Jan 16 '15 at 19:23

Simas

43,548
10
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116

Kirill Shalnov · Answer 3 · 2015-01-16T19:35:46.950

0

DatabaseHelper dbHelper;

you never initialize it, like this

DatabaseHelper dbHelper = new DatabaseHelper(context);

Or, I think, you can make createDataBase() and checkDataBase() static methods

edited Jan 16 '15 at 19:35

answered Jan 16 '15 at 19:29

Kirill Shalnov

2,216
1
19
21

you'll notice that the CurrentDay class does not know about any context. As for making `createDataBase` a static method, how do you propose to call `this.getReadableDatabase()` in it, then? – njzk2 Jan 16 '15 at 19:39
@njzk2 it was a hint that the context is needed. About static - calling constructor and return result instead of use "this", I can not offer here a listing of all the necessary changes in this case. Only the general idea. – Kirill Shalnov Jan 16 '15 at 19:46

score 0 · Answer 4 · answered Apr 27 '19 at 06:31

0

Initialize the dbHelper. dbHelper = new dbHelper(context);

answered Apr 27 '19 at 06:31

Thamal Wijetunge

1

NullpointerException when trying to create SQL Database

4 Answers4