How to sort GKTurnBasedMatch by most recently active?

Question

I am creating a simple word game with a menu screen in which I am displaying all of the user's active matches. I would like to sort this array of matches in order from most recently to least recently active, but the only timestamp property associated with players taking turns is a property of GKTurnBasedParticipant...GKTurnBasedMatch has no useful sorting property.

GKTurnBasedMatch has an array of GKTurnBasedParticipant objects as a property, so I would certainly be able to come up with some sort of solution, but I can't think of anything that wouldn't be really messy and inefficient. Is there any way something simple like NSPredicate could be used in a case like this to drill down into each array of participants, look at the latest timestamp and sort all the matches in one go?

Answer 1

I don't have an NSPredicate-based solution, or probably anything as elegant as you had hoped, but I ran into the same issue and wrote my own solution and it wasn't actually that bad.

My solution is for a game that can only have two participants, so modify accordingly, but here is the code I ended up using:

[myGamesArray sortUsingComparator:^NSComparisonResult(CHGame *game1, 
                                                      CHGame *game2) {

    if (YES == [game1 localPlayersTurn] && NO == [game2 localPlayersTurn]) {
        return NSOrderedAscending;
    } else if (NO == [game1 localPlayersTurn] && YES == [game2 localPlayersTurn]) {
        return NSOrderedDescending;
    }

    NSDate *lm1 = [game1.match lastMove];
    NSDate *lm2 = [game2.match lastMove];
    if (lm1 != nil && lm2 != nil) {
        return [lm1 compare:lm2];
    }

    return NSOrderedSame;

}];

where CHGame is a custom class I built for my games (which have a GKTurnBasedMatch match property), and the instance method localPlayersTurn returns a BOOL indicating whether or not it is the local participant's turn or not.

And then I wrote a lastMove method in a category on GKTurnBasedMatch:

- (NSDate *)lastMove {
    GKTurnBasedParticipant *localParticipant, *otherParticipant;
    NSDate *lastMove;

    for (GKTurnBasedParticipant *participant in self.participants) {
        if (YES == [participant.playerID isEqualToString:[GKLocalPlayer localPlayer].playerID]) {
            localParticipant = participant;
        } else {
            otherParticipant = participant;
        }
    }

    if (localParticipant == self.currentParticipant) {
        lastMove = otherParticipant.lastTurnDate;
    } else {
        lastMove = localParticipant.lastTurnDate;
    }

    return lastMove;
}

Again, this only works for two total participants, but would be easy to modify for any number of them.

Hope this helps even though it's not exactly what you asked for.