Getting Errors while querying DB in Android

Question

I'm new to Android programming, and rusty in java! I've been working on a small program that ask users to input some stuff to EditText's and once the time stops or the user click's Finish button, it searches the database for the values the user set. That said, I'm getting errors in that part. :(

public class UserScreen extends Activity implements View.OnClickListener {

    public TextView tvCounter;
    public EditText input;
    public Button finish;

    public void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.gamescreen);

        tvCounter = (TextView) findViewById(R.id.tvCounter);
        finish = (Button) findViewById(R.id.bFinish);
        finish.setOnClickListener(this);

        new CountDownTimer(30000, 1000) {

            public void onTick(long millisUntilFinished) {
                tvCounter.setText("seconds remaining: "
                        + Long.toString(millisUntilFinished / 1000));
            }

            public void onFinish() {
                tvCounter.setText("done!");
                searchDB();
            }
        }.start();
    }

    private SQLiteDatabase database;
    private DatabaseHelper dbHelper;

    public void searchDB() {
        Object tableList[] = { "table1", "table2", "table3", "table4",
                "table5", "table6" };
        Object columnList[] = { "column1", "column2", "column3", "column4", "column5", "column6" };
        int pList[] = { R.id.et1, R.id.et2, R.id.et3,
                R.id.et4, R.id.et5, R.id.et6 };

        database = dbHelper.getReadableDatabase();
        Cursor cursor = null;

        for (int i = 0; i < tableList.length; i++) {

            input = (EditText) findViewById(pList[i]);
            String data = input.getText().toString();

            cursor = database.rawQuery("SELECT * FROM " + tableList[i]
                    + " WHERE " + pList[i] + " = " + columnList[i], null);

            String dbStuff = cursor.toString();
                        if (dbStuff == data) { 
                            tvCounter.setText("YEAH");
                        } 
                        else { 
                        tvCounter.setText("DAMN"); 
                        }
        }
        cursor.close();
    }

    public void onClick(View v) {
        // TODO Auto-generated method stub
        searchDB();
    }
}

And the Errors are:

07-28 17:43:59.385: E/AndroidRuntime(920): FATAL EXCEPTION: main
07-28 17:43:59.385: E/AndroidRuntime(920): java.lang.NullPointerException
07-28 17:43:59.385: E/AndroidRuntime(920): at com.example.androidgame.GameScreen.searchDB(GameScreen.java:56)
07-28 17:43:59.385: E/AndroidRuntime(920): at com.example.androidgame.GameScreen.onClick(GameScreen.java:84)
07-28 17:43:59.385: E/AndroidRuntime(920): at android.view.View.performClick(View.java:3511)
07-28 17:43:59.385: E/AndroidRuntime(920): at android.view.View$PerformClick.run(View.java:14105)
07-28 17:43:59.385: E/AndroidRuntime(920): at android.os.Handler.handleCallback(Handler.java:605)
07-28 17:43:59.385: E/AndroidRuntime(920): at android.os.Handler.dispatchMessage(Handler.java:92)
07-28 17:43:59.385: E/AndroidRuntime(920): at android.os.Looper.loop(Looper.java:137)
07-28 17:43:59.385: E/AndroidRuntime(920): at android.app.ActivityThread.main(ActivityThread.java:4424)
07-28 17:43:59.385: E/AndroidRuntime(920): at java.lang.reflect.Method.invokeNative(Native Method)
07-28 17:43:59.385: E/AndroidRuntime(920): at java.lang.reflect.Method.invoke(Method.java:511)
07-28 17:43:59.385: E/AndroidRuntime(920): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
07-28 17:43:59.385: E/AndroidRuntime(920): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
07-28 17:43:59.385: E/AndroidRuntime(920): at dalvik.system.NativeStart.main(Native Method)

Creation or acess to DB are in another class.

public class DBAccess extends Activity {

private DatabaseHelper databaseHelper;
private SQLiteDatabase db;


public void onCreate(Context context){
    databaseHelper = new DatabaseHelper(context);
    searchDB();
}

public void openDB(){
    db = databaseHelper.getWritableDatabase();
}
public void closeDB(){
    db.close();
}
public void searchDB(){
    Intent Scoring = getIntent();
    String rawdata[] = Scoring.getStringArrayExtra("data");
    openDB();
    Object tableList[] = { "table1", "table2", "table3", "table4", "table5", "table6" };
    Object columnList[] = { "KEY_COLUMN1", "KEY_COLUMN2", "KEY_COLUMN3", "KEY_COLUMN4", "KEY_COLUMN5",
    "KEY_COLUMN6" };

    int downScore = 0;
    int upScore = 0;
    String dbStuff;

    Cursor cursor = null;

    for (int i = 0; i < tableList.length; i++) {
        if(rawdata[i] == "niente")
            downScore = downScore + 5;
        else {
            cursor = db.rawQuery("SELECT * FROM " + tableList[i] + " WHERE " + rawdata[i] + " = " + columnList[i] , null);
        dbStuff = cursor.toString();
        if (i == 0)
             cursor.moveToFirst();
        else
            cursor.moveToNext();
        if(dbStuff == rawdata[i])
            upScore = upScore + 10;
        else
            downScore = downScore + 5;
        }
    }
    closeDB();
    cursor.close();
    Intent i = new Intent(this, ScoreScreen.class);
    i.putExtra("uScore", upScore);
    i.putExtra("dScore", downScore);
    }

}

CEO · Accepted Answer · 2012-07-29 17:14:15Z

1

Design-wise, separate DB construction and maintenance aspects, from the DB access layer itself.

For this, have 2 classes. 1) Put in DBHelper.java all the construction and maintenance, and 2) DBAccess.java have the methods to access the DB.

Below are code snippets for this... Note that the application (activities) themselves should know nothing and have no visibility about the construction of the DB itself (see visibility of DBHelper class itself), but instead only have full visibility to the simple access methods such as open, close, CRUD methods...

:

class DBHelper extends SQLiteOpenHelper {

    :
    :

    private SQLiteDatabase db;
    private static final int DATABASE_VERSION = 1;
    private static final String DB_NAME = "dbname.db";
    :
    :

}

public class DBAccess {

    :
    :

    private DBHelper dbHelper;
    private SQLiteDatabase db;

    :
    :

    public DBAccess(Context context) {
        dbHelper = new DBHelper(context);
    }

    /**
     * Open the database
     */
    public void openDB() {
        db = dbHelper.getWritableDatabase();
    }

    /**
     * Close the database
     */
    public void closeDB() {
        db.close();
    }

    :
    :
}

The activity the uses the DB, you can have a method called setupDB(), method that is called during the creation of the activity:

private void setupDB() {
    dbAccess = new DBAccess(this);
    dbAccess.openDB();
}

:

private void searchDB() {
    :

    mStatusList = dbAccess.selectAllStatus();

    :
}

:
:

edited Jul 29, 2012 at 17:14

answered Jul 28, 2012 at 21:26

CEO

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5 Comments

Sheep Over a year ago

CEO, thanks. Done what you said and it's almost great, but there's a problem with mStatusList = dbAccess.selectAllStatus(); it says is undefined for the type DBAccess. I also searched for it in android devs site and google too. Couldn't find it, and don't really know what it does.

Sheep Over a year ago

Ah! One more thing. To use the cursor I need to point it to SQLitedatabase, but that is in DBAccess class.

CEO Over a year ago

Yes, the above are code example snippets -- you need to define the proper methods in DBAccess; in my example the method is called selectAllStatus()... Instead of that, use your own method. The idea is that the cursor etc is within DBAccess, within a method that will return the container of objects. In your case such method is searchDB() but that should return a container (a list) of objects, in your case, Strings (dbStuff) which you will process, in your case display tvCounter.setText("YEAH");

Sheep Over a year ago

Ah! Thank you! Though it was an android some kind of function. Really made a diference, it seems all clear as water now! :)

Sheep Over a year ago

Well, unfortunately it was almost as clear as water... I altered some stuff from the sample you gave me, specialy the public DBAccess() {} to public void onCreate() {}, so i could pass string[] data with an intent. So, this time there's no error message, at least not a red one. But there's nothing showing up when I pass some values to next class that shows the results. I hope you or someone kind enough can spot what I made stupidly wrong!

Todd Davies · Accepted Answer · 2012-07-28 18:04:52Z

0

You need to initialise your database and it's helper in onCreate():

  database = new SQLiteDatabase();
  dbHelper = new DatabaseHelper();

answered Jul 28, 2012 at 18:04

Todd Davies

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5 Comments

Sam Over a year ago

database is initialized here; database = dbHelper.getReadableDatabase(); but dbHelper still needs to be created. They should be closed afterwards as well.

Sheep Over a year ago

Thanks both for replying! But I'm getting an error in database = new SQLiteDatabase(); -> The constructor SQLiteDatabase() isn't visible. Sam, I'm not getting what your saying with the dbHelper needs to be created.

Todd Davies Over a year ago

Try database = new SQLiteDatabase(context, DATABASE_NAME, null, 1);

Sheep Over a year ago

Thanks Todd, but I get an error in context saying: context can't be resolved to a variable. Well, I tried searching android developers site, and it's pretty dificult to get what you want. So I don't, know why is there a context.

Todd Davies Over a year ago

Instead of context use this

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