Cursor in Android having issues with SqliteDatabase

Question

This is the Adapter Class I am using to Insert or Get Data from the SQLite Database. There is a method for inserting the data and a method for getting the data.

In the getData method, I return a cursor and handle it in some other class but the problem I face is difficult to understand from my perspective.

When I get the data using the query function of SqliteDatabase it returns me a Cursor so, in other words, the cursor has a subset of the some table inside the database. The work of Database Object is over so I close it and then return the Cursor. The function works without any problem but the cursor returned on the other side is empty.

Log displayed:

java.lang.IllegalStateException: Cannot perform this operation because the connection pool has been closed.

If I remove the line:

db.close();

then everything works fine, but some point in time it says leak in the database if I call getData() function more number of times.

public class DatabaseAdapter {


DatabaseHelper helper;

public  DatabaseAdapter (Context context) {

        helper = new DatabaseHelper(context);



}

public long insertData(String username, String domain, String crypt) {
    SQLiteDatabase db = helper.getWritableDatabase();
    ContentValues values = new ContentValues();
    values.put(DatabaseHelper.USERNAME, username);
    values.put(DatabaseHelper.DOMAIN, domain);
    values.put(DatabaseHelper.CRYPT, crypt);
    long id = db.insert(DatabaseHelper.TABLE_NAME, null, values);
    db.close();
    return id;
}

public Cursor getData() {
    String[] columns = {DatabaseHelper.USERNAME, DatabaseHelper.DOMAIN, DatabaseHelper.CRYPT};
    SQLiteDatabase db = helper.getReadableDatabase();
    Cursor c = db.query(DatabaseHelper.TABLE_NAME, columns, null, null, null, null, null);
   db.close(); // This line is the problem.

    return c;

}

public boolean deleteRow(SavedInformation information) {
    String[] array = {information.getUsername(), information.getDomainName(), information.getCryptPassword()};
    SQLiteDatabase db = helper.getWritableDatabase();
    db.delete(DatabaseHelper.TABLE_NAME, "" + DatabaseHelper.USERNAME + " = ? AND " + DatabaseHelper.DOMAIN + " = ? AND " + DatabaseHelper.CRYPT + " = ?", array);

    return true;
}


static class DatabaseHelper extends SQLiteOpenHelper {


    private static final String DATABASE_NAME = "Data_HASH";
    private static final int DATABASE_VERSION = 1;
    private static final String TABLE_NAME = "HASH";

    /*DATABASE COLUMNS */
    private static final String UID = "_id";
    private static final String USERNAME = "username";
    private static final String DOMAIN = "domain";
    private static final String CRYPT = "crypt";


    /*DATABASE CREATE QUERY */
    private static final String CREATE_TABLE = "CREATE TABLE " + TABLE_NAME + " (" + UID + " INTEGER PRIMARY KEY AUTOINCREMENT," + USERNAME + " VARCHAR," + DOMAIN + " VARCHAR," + CRYPT + " VARCHAR);";

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

    }

    @Override
    public void onCreate(SQLiteDatabase db) {

        try {
            db.execSQL(CREATE_TABLE);
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        try {
            db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
            onCreate(db);
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}}

Answer 1

If I'm not mistaken, you shouldn't use the cursor in any other class if you're just getting data from the database. Create a data model and return the data from the method, not a cursor reference.

Answer 2

你应该避免多次调用open / close光标。