Database resource leaks

The current code logs warnings about resource leaks, in particular database leaks.

E.g., in

    public FolderInfo getFolderInfo(long folderID) {
        SQLiteQueryBuilder qb = new SQLiteQueryBuilder();

        qb.setTables(FOLDER_TABLE_NAME);
        qb.appendWhere(FolderColumns._ID + "=" + folderID);

        SQLiteDatabase db = mOpenHelper.getReadableDatabase(); // XXX
        try (Cursor c = qb.query(db, null, null, null, null, null, null)) { // XXX
            if (c.moveToFirst()) {
                long id = c.getLong(c.getColumnIndex(FolderColumns._ID));
                String name = c.getString(c.getColumnIndex(FolderColumns.NAME));

                FolderInfo folderInfo = new FolderInfo();
                folderInfo.id = id;
                folderInfo.name = name;

                return folderInfo;
            } else {
                return null;
            }
        }
    }

the db handle is leaked because db.close() is not called.

The two lines marked XXX can be replaced with:

        try (SQLiteDatabase db = mOpenHelper.getReadableDatabase(); Cursor c = qb.query(db, null, null, null, null, null, null)) {

which will use try-with-resources and close db when it goes out of scope too. That solves some of the problems, but I've noticed that getFolderList leaks as well:

    public Cursor getFolderList() {
        SQLiteQueryBuilder qb = new SQLiteQueryBuilder();

        qb.setTables(FOLDER_TABLE_NAME);

        SQLiteDatabase db = mOpenHelper.getReadableDatabase();
        return qb.query(db, null, null, null, null, null, "created ASC");
    }

I suspect the "correct" fix is write the database handling in terms of https://developer.android.com/reference/androidx/lifecycle/ViewModel and https://developer.android.com/reference/androidx/lifecycle/LiveData, which I think are supposed to resolve issues like this.

ogarcia / opensudoku

Database resource leaks #129