Retrieve list of songs ordered by last play time in iOS

Question

I need to obtain a list of the N most recently played songs from an iOS device, in order.

The only way I can imagine doing it, at the moment, is by getting all the songs through an MPMediaQuery and manually sort them by lastPlayedDate.

This is a potentially expensive operation and I was wondering if there was a better approach.

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Edit: After some tests, this is a very expensive operation. On a test library of 2500 songs, it took around 20 seconds to:

1. Get all the songs.
2. Assign a date to all songs that had never played (January 1 1970).
3. Order them by date.
4. Fetch the first N entries.

Any suggestion of improvements would be appreciated.

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Edit 2: Solved now, but just for the record here's what I was doing.

I was sorting using a block as described here: https://stackoverflow.com/a/805589/112702. Simply changing the sorting method to what's in Bryan's answer improved my speed by nearly 20 times on an iPod Touch 3.

Answer 1

One way is to take the array of MPMediaItems you get from the MPMediaQuery and sort it by MPMediaItemPropertyLastPlayedDate using an NSSortDescriptor:

NSTimeInterval start  = [[NSDate date] timeIntervalSince1970];

MPMediaQuery *songsQuery = [MPMediaQuery songsQuery];
NSArray *songsArray = [songsQuery items];

NSSortDescriptor *sorter = [NSSortDescriptor sortDescriptorWithKey:MPMediaItemPropertyLastPlayedDate
                                                         ascending:NO];
NSArray *sortedSongsArray = [songsArray sortedArrayUsingDescriptors:@[sorter]];

NSTimeInterval finish = [[NSDate date] timeIntervalSince1970];
NSLog(@"Execution took %f seconds.", finish - start);

This sorts the new array by most recently played first. I tested this on a iPhone 4S using 2000 songs and it took .98 seconds.