Question

What is the best way to buffer incoming events/notifications your iPhone app is observing so as not to trigger event code for each event? A code sample would be great…

e.g. would it be to create an NSMutableArray in the controller to add each event to, and for each event that comes in it triggers a count down time for 2 seconds, so the timer countdown would trigger the events handling code…in which case what would be the best Objective-C classes to use for such a buffer/timer/countdown…

background – in my case it the events from “EKEventStoreChangedNotification” that I handle, but noting there are multiple that can come through for the same single calendar item change (well as far as i can tell)

Answer 1

attach an object to your main run loop (typically via a timer). the object receives, collects, filters, and coalesces the events as needed.

something like this would be a starting point (not compiled):

@interface MONEventHandler : NSObject
{
    NSMutableArray * events;
    NSRecursiveLock * lock;
}

@end

@implementation MONEventHandler

- (id)init
{
    self = [super init];
    if (nil != self) {
        events = [NSMutableArray new];
        lock = [NSRecursiveLock new];
        /* begin listening for incoming events */
    }
    return self;
}

- (void)dealloc
{
/* stop listening for incoming events */
    [lock release], lock = nil;
    [events release], events = nil;
    [super dealloc];
}

- (void)postEvents:(NSTimer *)timer
{
    [lock lock];
    /* ... clear out self.events here ... */
    [lock unlock];
}

/* a few methods for your event entries, or callbacks */

@end

Now create the timer and add it to the main run loop:

/* call me on main thread ONLY */
void SetupEventHandler() {
    MONEventHandler * eventHandler = [MONEventHandler new];
    NSTimeInterval seconds = 0.100; /* 10Hz */
    NSTimer * timer = [NSTimer scheduledTimerWithTimeInterval:seconds target:eventHandler selector:@selector(postEvents:) userInfo:nil repeats:YES];
    /* you will need timer if you want to explicitly stop updates or destroy eventHandler. you do this by invalidating the timer. you can also access it from postEvents: */
   [eventHandler release];
}