How to close a cursor used in a for loop

问题

Background

I have a cursor used as follows:

        for (int n=0; n<num_songs; n++) {
            boolean isChecked = checked_positions.get(n);
            if (isChecked) {
                Cursor cursor = (Cursor) getListView().getItemAtPosition(n);
                String artist = cursor.getString(cursor.getColumnIndex(MediaStore.Audio.Media.ARTIST));
                String title = cursor.getString(cursor.getColumnIndex(MediaStore.Audio.Media.TITLE));
                cursor.close();
                //save artist and title strings to file...
            }
        }

This gives a StaleDataException on the second time round the loop when it tries to reuse the closed cursor. If I remove cursor.close() it runs fine but I get a "Cursor finalized without prior close" warning.

Research

The advice in this answer: https://stackoverflow.com/a/18107638/1977132 is to set the cursor to null cursor.close(); cursor = null; presumably so a new cursor can be created, but it makes no difference, the second time round the loop it still gives a StaleDataException.

I've already tried...

I tried moving it outside the loop as follows:

        Cursor cursor;
        for (int n=0; n<num_songs; n++) {
            boolean isChecked = checked_positions.get(n);
            if (isChecked) {
                cursor = (Cursor) getListView().getItemAtPosition(n);
                String artist = cursor.getString(cursor.getColumnIndex(MediaStore.Audio.Media.ARTIST));
                String title = cursor.getString(cursor.getColumnIndex(MediaStore.Audio.Media.TITLE));
                //save artist and title strings to file...
            }
        }
        cursor.close();

but this wouldn't compile with the error "cursor might not have been initialized".

Question

My question is how do I correctly use and close a cursor within a loop.

回答1:

Try this

Cursor cursor = null;
for (int n=0; n<num_songs; n++) {
    boolean isChecked = checked_positions.get(n);
    if (isChecked) {
        cursor = (Cursor) getListView().getItemAtPosition(n);
        String artist = cursor.getString(cursor.getColumnIndex(MediaStore.Audio.Media.ARTIST));
        String title = cursor.getString(cursor.getColumnIndex(MediaStore.Audio.Media.TITLE));
        //save artist and title strings to file...
    }
}
if(cursor != null)
    cursor.close();

回答2:

This is the proper way to close cursor:

    Cursor cursor = null;
    try{
        for (int n=0; n<num_songs; n++) {
            boolean isChecked = checked_positions.get(n);
            if (isChecked) {
                cursor = (Cursor) getListView().getItemAtPosition(n);
                String artist = cursor.getString(cursor.getColumnIndex(MediaStore.Audio.Media.ARTIST));
                String title = cursor.getString(cursor.getColumnIndex(MediaStore.Audio.Media.TITLE));
                //save artist and title strings to file...
            }
        }
    } finally {
        if(cursor != null){
            cursor.close();
        }
    }

来源：https://stackoverflow.com/questions/32201617/how-to-close-a-cursor-used-in-a-for-loop

标签

android

android-cursor

staledataexception