vendredi 18 mars 2016

Android - Retrieving random entry from SQLite Database?

I'm new to this. I'm trying to write a database and return a random entry from the database.

My question: How I can random query?

public class    QuizHelper extends SQLiteOpenHelper {
private static final int DATABASE_VERSION = 1;
// Database Name
private static final String DATABASE_NAME = "mathsone";
// tasks table name
private static final String TABLE_QUEST = "quest";
// tasks Table Columns names
private static final String KEY_ID = "qid";
private static final String KEY_QUES = "question";
private static final String KEY_ANSWER = "answer"; // correct option
private static final String KEY_OPTA = "opta"; // option a
private static final String KEY_OPTB = "optb"; // option b
private static final String KEY_OPTC = "optc"; // option c

private SQLiteDatabase dbase;

public QuizHelper(Context context) {
    super(context, DATABASE_NAME, null, DATABASE_VERSION);
}

@Override
public void onCreate(SQLiteDatabase db) {
    dbase = db;
    String sql = "CREATE TABLE IF NOT EXISTS " + TABLE_QUEST + " ( "
            + KEY_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " + KEY_QUES
            + " TEXT, " + KEY_ANSWER + " TEXT, " + KEY_OPTA + " TEXT, "
            + KEY_OPTB + " TEXT, " + KEY_OPTC + " TEXT)";
    db.execSQL(sql);
    addQuestion();
    // db.close();
}

private void addQuestion() {
    Question q1 = new Question("5*2*8 = ?", "7", "8", "10", "10");
    this.addQuestion(q1);
    Question q2 = new Question("2+18 = ?", "18", "19", "20", "20");
    this.addQuestion(q2);
    Question q3 = new Question("10-3 = ?", "6", "7", "8", "7");
    this.addQuestion(q3);
    Question q4 = new Question("5+7 = ?", "12", "13", "14", "12");
    this.addQuestion(q4);
    Question q5 = new Question("3-1 = ?", "1", "3", "2", "2");
    this.addQuestion(q5);
    Question q6 = new Question("0+1 = ?", "1", "0", "10", "1");
    this.addQuestion(q6);
    Question q7 = new Question("9-9 = ?", "0", "9", "1", "0");
    this.addQuestion(q7);
    Question q8 = new Question("3+6 = ?", "8", "7", "9", "9");
    this.addQuestion(q8);
    Question q9 = new Question("1+5 = ?", "6", "7", "5", "6");
    this.addQuestion(q9);
    Question q10 = new Question("7-5 = ?", "3", "2", "6", "2");
    this.addQuestion(q10);
    Question q11 = new Question("7-2 = ?", "7", "6", "5", "5");
    this.addQuestion(q11);
    Question q12 = new Question("3+5 = ?", "8", "7", "5", "8");
    this.addQuestion(q12);
    Question q13 = new Question("0+6 = ?", "7", "6", "5", "6");
    this.addQuestion(q13);
    Question q14 = new Question("12-10 = ?", "1", "2", "3", "2");
    this.addQuestion(q14);
    Question q15 = new Question("12+2 = ?", "14", "15", "16", "14");
    this.addQuestion(q15);
    Question q16 = new Question("2-1 = ?", "2", "1", "0", "1");
    this.addQuestion(q16);
    Question q17 = new Question("6-6 = ?", "6", "12", "0", "0");
    this.addQuestion(q17);
    Question q18 = new Question("5-1 = ?", "4", "3", "2", "4");
    this.addQuestion(q18);
    Question q19 = new Question("4+2 = ?", "6", "7", "5", "6");
    this.addQuestion(q19);
    Question q20 = new Question("5+1 = ?", "6", "7", "5", "6");
    this.addQuestion(q20);
    Question q21 = new Question("5-4 = ?", "5", "4", "1", "1");
    this.addQuestion(q21);
    // END
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldV, int newV) {
    // Drop older table if existed
    db.execSQL("DROP TABLE IF EXISTS " + TABLE_QUEST);
    // Create tables again
    onCreate(db);
}

// Adding new question
public void addQuestion(Question quest) {
    // SQLiteDatabase db = this.getWritableDatabase();
    ContentValues values = new ContentValues();
    values.put(KEY_QUES, quest.getQUESTION());
    values.put(KEY_ANSWER, quest.getANSWER());
    values.put(KEY_OPTA, quest.getOPTA());
    values.put(KEY_OPTB, quest.getOPTB());
    values.put(KEY_OPTC, quest.getOPTC());

    // Inserting Row
    dbase.insert(TABLE_QUEST, null, values);
}

public List<Question> getAllQuestions() {
    List<Question> quesList = new ArrayList<Question>();
    // Select All Query
    String selectQuery = "SELECT  * FROM " + TABLE_QUEST;
    dbase = this.getReadableDatabase();
    Cursor cursor = dbase.rawQuery(selectQuery, null);
    // looping through all rows and adding to list
    if (cursor.moveToFirst()) {
        do {
            Question quest = new Question();
            quest.setID(cursor.getInt(0));
            quest.setQUESTION(cursor.getString(1));
            quest.setANSWER(cursor.getString(2));
            quest.setOPTA(cursor.getString(3));
            quest.setOPTB(cursor.getString(4));
            quest.setOPTC(cursor.getString(5));

            quesList.add(quest);
        } while (cursor.moveToNext());
    }
    // return quest list
    return quesList;
}

This is the code that I put in my Randomize activity, and although it worked once for some reason, my program crashes every time I try to randomize again. The base is the List that I retrieved that contains all the recipe entry names. I figured since I used it to populate my ListView, I could use it again to access it in the randomize.

Should I try to get the value from the database directly? If so, how would I do that and can someone provide an example?




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