Question

Code for the DBHelper class:

class DBHelper extends SQLiteOpenHelper {

    private static final String DATABASE_PATH = Environment.getDataDirectory()
            + "/data/test.data/databases/";
    private static final String DATABASE_NAME = "test.sqlite3";
    private static final int SCHEMA_VERSION = 1;
    public static final String TABLE_NAME = "terran_builds";
    public static final String COLUMN_ID = "_id";
    public static final String COLUMN_NAME = "name";
    public static final String COLUMN_OVERVIEW = "overview";

    public SQLiteDatabase dbSqlite;

    private final Context myContext;

    public DBHelper(Context context) {
        super(context, DATABASE_NAME, null, SCHEMA_VERSION);
        this.myContext = context;
    }

    @Override
    public void onCreate(SQLiteDatabase db) {

    }

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

    }

    public void createDatabase() {
        createDB();
    }

    private void createDB() {

        boolean dbExist = DBExists();
        if (!dbExist) {

            this.getReadableDatabase();

            copyDBFromResource();

        }

    }

    private boolean DBExists() {
        SQLiteDatabase db = null;

        try {
            String databasePath = DATABASE_PATH + DATABASE_NAME;
            db = SQLiteDatabase.openDatabase(databasePath, null,
                    SQLiteDatabase.OPEN_READWRITE);
            db.setLocale(Locale.getDefault());
            db.setLockingEnabled(true);
            db.setVersion(1);
        } catch (SQLiteException e) {
            Log.e("SqlHelper", "database not found");
        }

        if (db != null) {

            db.close();
        }

        return db != null ? true : false;
    }

    private void copyDBFromResource() {

        InputStream inputStream = null;
        OutputStream outStream = null;
        String dbFilePath = DATABASE_PATH + DATABASE_NAME;

        try {

            inputStream = myContext.getAssets().open(DATABASE_NAME);

            outStream = new FileOutputStream(dbFilePath);

            byte[] buffer = new byte[1024];
            int length;
            while ((length = inputStream.read(buffer)) > 0) {
                outStream.write(buffer, 0, length);
            }
            outStream.flush();
            outStream.close();
            inputStream.close();
        } catch (IOException e) {

            throw new Error("Problem copying database from resource file.");
        }

    }

    public void openDataBase() throws SQLException {

        String myPath = DATABASE_PATH + DATABASE_NAME;
        dbSqlite = SQLiteDatabase.openDatabase(myPath, null,
                SQLiteDatabase.OPEN_READWRITE);
    }

    @Override
    public synchronized void close() {
        // TODO Auto-generated method stub

        if (dbSqlite != null) {
            dbSqlite.close();
        }
        super.close();
    }

    public Cursor getTerran() {

        SQLiteQueryBuilder queryBuilder = new SQLiteQueryBuilder();

        queryBuilder.setTables(TABLE_NAME);

        String[] asColumnsToReturn = new String[] { COLUMN_ID, COLUMN_NAME,
                COLUMN_OVERVIEW };

        Cursor mCursor = queryBuilder.query(dbSqlite, asColumnsToReturn, null,
                null, null, null, "name");

        return mCursor;
    }

    public String getName(Cursor c) {
        return (c.getString(1));
    }
}

Code for the Terran activity:

public class Terran extends Activity {

    private DBHelper dbHelp = null;
    private Cursor ourCursor = null;
    private DBAdapter adapter = null;

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        try {

            super.onCreate(savedInstanceState);
            setContentView(R.layout.terran_layout);

            // this is our listview element, obtained by id from our xml layout
            ListView myListView = (ListView) findViewById(R.id.tvterran);

            // create our database helper
            dbHelp = new DBHelper(this);
            // we call the create right afther initializing helper
            dbHelp.createDatabase();
            // open the database
            dbHelp.openDataBase();
            // get our cursor
            ourCursor = dbHelp.getTerran();

            // tell android to start managing cursor
            startManagingCursor(ourCursor);
            // create our adapter
            adapter = new DBAdapter(ourCursor);
            // set the adapter
            myListView.setAdapter(adapter);

        } catch (Exception e) {

            // send real error message
            Log.e("ERROR", "ERROR IN CODE: " + e.toString());

            e.printStackTrace();
        }
    }

    class DBAdapter extends CursorAdapter {
        DBAdapter(Cursor c) {
            super(Terran.this, c);
        }

        @Override
        public void bindView(View row, Context ctxt, Cursor c) {
            // TODO Auto-generated method stub
            terranHolder holder = (terranHolder) row.getTag();
            holder.populateFrom(c, dbHelp);

        }

        @Override
        public View newView(Context ctxt, Cursor c, ViewGroup parent) {
            // TODO Auto-generated method stub
            LayoutInflater inflater = getLayoutInflater();
            View row = inflater.inflate(R.layout.terran_layout, parent, false);
            terranHolder holder = new terranHolder(row);
            row.setTag(holder);
            return (row);
        }
    }

    static class terranHolder {
        private TextView name = null;

        terranHolder(View row) {
            name = (TextView) row.findViewById(R.id.tvterran);
        }

        void populateFrom(Cursor c, DBHelper r) {
            name.setText(r.getName(c));
        }
    }

}

Logcat exception:

01-30 20:07:13.765: E/ERROR(7153): ERROR IN CODE: java.lang.NullPointerException
01-30 20:07:13.775: W/System.err(7153): java.lang.NullPointerException
01-30 20:07:13.775: W/System.err(7153):     at com.subdeveloper.starcraftbuilds.Terran.onCreate(Terran.java:46)
01-30 20:07:13.775: W/System.err(7153):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
01-30 20:07:13.775: W/System.err(7153):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1623)
01-30 20:07:13.775: W/System.err(7153):     at android.app.ActivityThread.startActivityNow(ActivityThread.java:1499)
01-30 20:07:13.775: W/System.err(7153):     at android.app.LocalActivityManager.moveToState(LocalActivityManager.java:127)
01-30 20:07:13.775: W/System.err(7153):     at android.app.LocalActivityManager.startActivity(LocalActivityManager.java:339)
01-30 20:07:13.775: W/System.err(7153):     at android.widget.TabHost$IntentContentStrategy.getContentView(TabHost.java:731)
01-30 20:07:13.775: W/System.err(7153):     at android.widget.TabHost.setCurrentTab(TabHost.java:403)
01-30 20:07:13.775: W/System.err(7153):     at android.widget.TabHost.addTab(TabHost.java:242)

I can’t get the ListView to generate from the query results. From my debugging I understand that the error is in the Terran class on line 46. I can’t figure out what is wrong. Tested with other database, database connection works.

Answer 1

Your ListView is null that means that either don’t have a ListView with that id in your layout or android didn’t generate the proper id for the list and you have an old one that is incorrect.

Try to refresh the project, delete the R class from the folder gen so that the ID are generated again, restart the IDE.