I am writing a gallery-type application for Android. In the "main activity" I have a GridView that I want to upload / fill in with thumbnails from photos on the device. So I wrote a ContentProvider where the request method returns the cursor from MediaStore.Media.Thumbnails.
However, I also want to display some metadata from MediaStore.Media.Images. To do this, I ended up using CursorJoiner to join c_thumbs and c_images on ID. The only problem with this is that CursorJoiner requires that the input cursors are already sorted (sorted) by join key (ID) in ascending order. What I want is the latest photos from above, but is there a way to sort the existing (already loaded) cursor?
As an alternative to CursorJoiner, maybe I could join SQL? Is it possible to join MediaStore.Images.Media and MediaStore.Images.Thumbnails in one request (and how does it work)?
Apparently this is not possible.
// split projection into MediaStore and MediaStore.Thumbs parts ArrayList<String> MS_proj = new ArrayList<>(); ArrayList<String> MS_proj_thumbs = new ArrayList<>(); for (String f : projection) { if (PhotoContract.ThumbEntry.COL_TYPES.get(f).equals(PhotoContract.TARGET_MEDIASTORE)) { MS_proj.add(f); } else { MS_proj_thumbs.add(f); } } String[] MS_proj_thumbs_array = new String[MS_proj_thumbs.size()]; MS_proj_thumbs_array = MS_proj_thumbs.toArray(MS_proj_thumbs_array); // add _ID column to Images.Media projection, for use in JOIN MS_proj.add("_ID"); String[] MS_proj_array = new String[MS_proj.size()]; MS_proj_array = MS_proj.toArray(MS_proj_array); Uri baseUri; // first, get cursor from MediaStore.Images.Thumbnails containing all thumbnails baseUri = MediaStore.Images.Thumbnails.EXTERNAL_CONTENT_URI; Log.v("TEST", "Thumb: order by " + PhotoContract.ThumbEntry.COLUMN_DATE); Cursor c_thumbs = getContext().getContentResolver().query(baseUri, MS_proj_thumbs_array, null, null, PhotoContract.ThumbEntry.COLUMN_IMAGE_ID); if (c_thumbs == null || !c_thumbs.moveToFirst()) { Log.v("TEST", "MediaStore.Thumbnails cursor contains no data..."); return null; } // then, get cursor from MediaStore.Images.Media (for TITLE and DESCRIPTION etc) // add _ID column to query baseUri = MediaStore.Images.Media.EXTERNAL_CONTENT_URI; Cursor c_images = getContext().getContentResolver().query(baseUri, MS_proj_array, null, null, PhotoContract.ThumbEntry.COLUMN_IMAGE_PK); if (c_images == null || !c_images.moveToFirst()) { Log.v("TEST", "MediaStore.Images cursor contains no data..."); return null; } // join these and return // the join is on images._ID = thumbnails.IMAGE_ID CursorJoiner joiner = new CursorJoiner( c_thumbs, new String[] { PhotoContract.ThumbEntry.COLUMN_IMAGE_ID }, c_images, new String[] { PhotoContract.ThumbEntry.COLUMN_IMAGE_PK } ); MatrixCursor retCursor = new MatrixCursor(projection); /* Does a join on two cursors using the specified columns. The cursors must already be sorted on each of the specified columns in ascending order. This joiner only supports the case where the tuple of key column values is unique. */ for (CursorJoiner.Result joinerResult : joiner) { switch (joinerResult) { case LEFT: // handle case where a row in cursorA is unique break; case RIGHT: // handle case where a row in cursorB is unique break; case BOTH: // handle case where a row with the same key is in both cursors retCursor.addRow(new Object[]{ c_thumbs.getLong(0), // ID c_thumbs.getString(1), // data c_thumbs.getLong(2), // image id c_images.getString(0), // title c_images.getString(1), // desc c_images.getLong(2) // date }); break; } } // https://stackoverflow.com/questions/12065606/getcontentresolver-query-cause-cursorwrapperinner-warning c_thumbs.close(); c_images.close(); return retCursor;
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