NSArrayController with throttled rearrangement When frequently changing objects monitored by an NSArrayController with auto rearrangement enabled, you can quickly run into an annoying performance issue caused by the array controller rearranging with unnecessary frequency. This subclass allows you to temporarily suspend rearrangement and/or throt…

TWNSArrayController.h

@interface TWNSArrayController : NSArrayController

@property (nonatomic) BOOL throttleRearrangement;
@property (nonatomic) CGFloat rearrangementThrottleInterval;

-(void)suspendRearrangement;
-(void)resumeRearrangement;

@end

TWNSArrayController.m

@implementation TWNSArrayController {
    BOOL _canRearrange;
    int _suspensionRequestCount;
    BOOL _pendingRearrangement;
    BOOL _throttleIntervalPassed;
    NSTimer *_canRearrangeTimer;
}

-(id)init {
    if ((self = [super init])) {
        _canRearrange = YES;
	_throttleIntervalPassed = YES;
	_suspensionRequestCount = 0;
	_rearrangementThrottleInterval = 1;
    }
    return self;
}

-(void)suspendRearrangement {
    _suspensionRequestCount += 1;
    _canRearrange = NO;
}
-(void)resumeRearrangement {
    _suspensionRequestCount -= 1;
    if (_suspensionRequestCount < 0) // Unbalanced call to resumeRearrangement
        _suspensionRequestCount = 0;
    if (_suspensionRequestCount == 0) {
        _canRearrange = YES;
	if (_pendingRearrangement)
            self rearrangeObjects];
    }
}

-(void)rearrangeObjects {
    [_canRearrangeTimer invalidate];

    if (!_canRearrange) {
        _pendingRearrangement = YES;
        return;
    }

    _pendingRearrangement = NO;
    _canRearrangeTimer = [NSTimer scheduledTimerWithTimeInterval:self.rearrangementThrottleInterval
                                                          target:self
                                                        selector:@selector(throttleIntervalPassed:)
                                                        userInfo:nil
                                                         repeats:NO];

    if (!_throttleIntervalPassed && self.throttleRearrangement)
        return;

    _throttleIntervalPassed = NO;
    [super rearrangeObjects];
}

-(void)throttleIntervalPassed:(NSTimer *)timer {
    _throttleIntervalPassed = YES;
    if (self.throttleRearrangement && _pendingRearrangement)
    [self rearrangeObjects];
}

@end