Querying the MediaStore: Joining thumbnails and images (on ID)

Question

I\'m working on a \"photo gallery\"-type app for Android. It started as a Final Project for the Developing Android Apps at Udacity, so it\'s overall structure (activities, conte

Answer 1

The accepted answer got me started on this question, but it contain a couple of small errors.

case LEFT:
            // handle case where a row in cursorA is unique
            // images is unique (missing thumbnail)
case RIGHT:
            // handle case where a row in cursorB is unique
            // thumbs is unique (missing image)

These are backwards. The documentation contradicts itself, and is likely where the mistake got made. From the source code of CursorJoiner:

case LEFT:
        // handle case where a row in cursorA is unique

Then in the enum for Result from the source code:

public enum Result {
    /** The row currently pointed to by the left cursor is unique */
    RIGHT,
    /** The row currently pointed to by the right cursor is unique */
    LEFT,
    /** The rows pointed to by both cursors are the same */
    BOTH
}

So I am guessing this is why you were force incrementing the cursors.

 //compensate for CursorJoiner expecting cursors ordered ascending...
                c_images.moveToNext();
                c_thumbs.moveToPrevious();

The iterator in CursorJoiner automatically increments the cursors for you.

This should be the working code (This code will also merge internal storage and external storage into a single cursor):

        Cursor[] thumbs = new Cursor[2];
        thumbs[0] = mActivity.getContentResolver().query(
                MediaStore.Images.Thumbnails.EXTERNAL_CONTENT_URI,
                new String[]{
                        MediaStore.Images.Thumbnails._ID ,
                        MediaStore.Images.Thumbnails.IMAGE_ID,
                        MediaStore.Images.Thumbnails.DATA
                },
                null,
                null,
                MediaStore.Images.Thumbnails.IMAGE_ID + "*(-1)"
        );
        thumbs[1] = mActivity.getContentResolver().query(
                MediaStore.Images.Thumbnails.INTERNAL_CONTENT_URI,
                new String[]{
                        MediaStore.Images.Thumbnails._ID ,
                        MediaStore.Images.Thumbnails.IMAGE_ID,
                        MediaStore.Images.Thumbnails.DATA
                },
                null,
                null,
                MediaStore.Images.Thumbnails.IMAGE_ID + "*(-1)"
        );
        Cursor thumbCursor = new MergeCursor(thumbs);
        Cursor[] cursors = new Cursor[2];
        cursors[0] = mActivity.getContentResolver().query(
                MediaStore.Images.Media.EXTERNAL_CONTENT_URI,
                new String[]{
                        MediaStore.Images.Media._ID,
                        MediaStore.Images.Media.DATA,
                        MediaStore.Images.Media.ORIENTATION,
                        MediaStore.Images.Media.BUCKET_DISPLAY_NAME,
                        MediaStore.Images.Media.BUCKET_ID,
                        MediaStore.Images.Media.MIME_TYPE
                },
                null,
                null,
                MediaStore.Images.Media._ID + "*(-1)"
        );
        cursors[1] = mActivity.getContentResolver().query(
                MediaStore.Images.Media.INTERNAL_CONTENT_URI,
                new String[]{
                        MediaStore.Images.Media._ID,
                        MediaStore.Images.Media.DATA,
                        MediaStore.Images.Media.ORIENTATION,
                        MediaStore.Images.Media.BUCKET_DISPLAY_NAME,
                        MediaStore.Images.Media.BUCKET_ID,
                        MediaStore.Images.Media.MIME_TYPE
                },
                null,
                null,
                MediaStore.Images.Media._ID + "*(-1)"
        );
        Cursor photoCursor = new MergeCursor(cursors);
        CursorJoiner cursorJoiner = new CursorJoiner(
                thumbCursor,
                new String[]{
                        MediaStore.Images.Thumbnails.IMAGE_ID
                },
                photoCursor,
                new String[]{
                        MediaStore.Images.Media._ID,
                }
        );
        Cursor finalCursor= new MatrixCursor(new String[]{
                MediaStore.Images.Media._ID,
                MediaStore.Images.Media.DATA,
                MediaStore.Images.Media.ORIENTATION,
                MediaStore.Images.Media.BUCKET_DISPLAY_NAME,
                MediaStore.Images.Media.BUCKET_ID,
                MediaStore.Images.Media.MIME_TYPE,
                "thumb_data"
        });
        for (CursorJoiner.Result joinerResult : cursorJoiner) {
            switch (joinerResult) {
                case RIGHT:
                    finalCursor.addRow(new Object[]{
                            photoCursor.getLong(photoCursor.getColumnIndex(MediaStore.Images.Media._ID)),
                            photoCursor.getString(photoCursor.getColumnIndex(MediaStore.Images.Media.DATA)),
                            photoCursor.getLong(photoCursor.getColumnIndex(MediaStore.Images.Media.ORIENTATION)),
                            photoCursor.getString(photoCursor.getColumnIndex(MediaStore.Images.Media.BUCKET_DISPLAY_NAME)),
                            photoCursor.getLong(photoCursor.getColumnIndex(MediaStore.Images.Media.BUCKET_ID)),
                            photoCursor.getString(photoCursor.getColumnIndex(MediaStore.Images.Media.MIME_TYPE)),
                            null
                    });
                    break;
                case BOTH:
                    finalCursor.addRow(new Object[]{
                            photoCursor.getLong(photoCursor.getColumnIndex(MediaStore.Images.Media._ID)),
                            photoCursor.getString(photoCursor.getColumnIndex(MediaStore.Images.Media.DATA)),
                            photoCursor.getLong(photoCursor.getColumnIndex(MediaStore.Images.Media.ORIENTATION)),
                            photoCursor.getString(photoCursor.getColumnIndex(MediaStore.Images.Media.BUCKET_DISPLAY_NAME)),
                            photoCursor.getLong(photoCursor.getColumnIndex(MediaStore.Images.Media.BUCKET_ID)),
                            photoCursor.getString(photoCursor.getColumnIndex(MediaStore.Images.Media.MIME_TYPE)),
                            thumbCursor.getString(thumbCursor.getColumnIndex(MediaStore.Images.Thumbnails.DATA)),
                    });
                    break;
            }

        }
        photoCursor.close();
        thumbCursor.close();