java.lang.IllegalStateException: attempt to re-open an already-closed object: SQLiteDatabase: data/data/http://ift.tt/1D6Eqfl

I design app but if click in imageview and show image in new activity if back app force close.

database:

public String Display(int row,int fild){
        Cursor cu= mydb.query("ps", null, null, null, null, null, null);
        cu.moveToPosition(row);
        String name=cu.getString(fild);
        cu.close();
        return name;
    }