Is Android Cursor.moveToNext() Documentation Correct?

Question

boolean android.database.Cursor.moveToNext() documentation says:

http://developer.android.com/reference/android/database/Cursor.html#moveToNext%28%29

Move th

Answer 1

It appears to be down to the Android implementation of AbstractCursor and it remains broken in Jellybean.

I implemented the following unit test to demonstrate the problem to myself using a MatrixCursor:

@Test
public void testCursor() {
  MatrixCursor cursor = new MatrixCursor(new String[] { "id" });
  for (String s : new String[] { "1", "2", "3" }) {
    cursor.addRow(new String[] { s });
  }

  cursor.moveToPosition(0);
  assertThat(cursor.moveToPrevious(), is(true));

  cursor.moveToPosition(cursor.getCount()-1);
  assertThat(cursor.moveToNext(), is(true));

  assertThat(cursor.moveToPosition(c.getCount()), is(true));
  assertThat(cursor.moveToPosition(-1), is(true));
}

All assertions fail, contrary to the documentation for moveToNext, moveToPrevious and moveToPosition.

Reading the code at API 16 for AbstractCursor.moveToPosition(int position) it appears to be intentional behaviour, ie the methods explicitly return false in these cases, contrary to the documentation.

As a side note, since the Android code sat on existing devices in the wild cannot be changed, I have taken the approach of writing my code to match the behaviour of the existing Android implementation, not the documentation. ie. When implementing my own Cursors / CursorWrappers, I override the methods and write my own javadoc describing the departure from the existing documentation. This way, my Cursors / CursorWrappers remain interchangeable with existing Android cursors without breaking run-time behaviour.