Question

I’m trying to understand how cursors work and I don’t understand a portion of this code —
(lifted off of http://www.vogella.com/articles/AndroidSQLite/article.html)

public Comment createComment(String comment) {
        ContentValues values = new ContentValues();
        values.put(MySQLiteHelper.COLUMN_COMMENT, comment);
        long insertId = database.insert(MySQLiteHelper.TABLE_COMMENTS, null,
                values);
        Cursor cursor = database.query(MySQLiteHelper.TABLE_COMMENTS,
                allColumns, MySQLiteHelper.COLUMN_ID + " = " + insertId, null,
                null, null, null);
        cursor.moveToFirst();
        Comment newComment = cursorToComment(cursor);
        cursor.close();
        return newComment;
    }

Can someone please explain what is going on here?
This is what I THINK is going on – He is inserting values into the table under the column named comment. He then does a query setting the cursor to where he added the comment in the table.

Then I am confused on why he does cursor.moveToFirst(). Isn’t the cursor pointing to the current comment he just added? I thought he is trying to return the comment he just inserted into the table, so couldn’t he just remove the moveToFirst() method?

Answer 1

  Cursor cursor = database.query(MySQLiteHelper.TABLE_COMMENTS,
                allColumns, MySQLiteHelper.COLUMN_ID + " = " + insertId, null,
                null, null, null);

Returns results are cursor object.

 cursor.moveToFirst();

Make sure your are pointing to first element in the cursor object (or) cursor is not empty.

 Comment newComment = cursorToComment(cursor);

Calling another method to go through the cursor and perform what ever logic coded inside the method, which return Comment object.

 cursor.close();

Close the cursor, so that it would be eligible GC and memeory will be free.

 return newComment;

Return the comment object to caller.