How to call a block after a delay

On iOS and on OS X you sometimes need the User Interface to update after a short delay. The old way of doing it was calling the performSelector:withObject:afterDelay: selector on any NSObject subclass but that requires defining a new method in your class and you can only pass one object as a parameter.

Instead, you can use dispatch_after from the Grand Central Dispatch APIs to execute code within a block after a certain time interval. Don’t be afraid, it might be low-level C but you can cut and paste and just put your code inside and it will retain the variable scope that blocks usually do!

double delayInSeconds = 0.5;
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){

  // Your code here

});

Core Animation stops animation on app relaunch

On one of my projects I discovered a bug in a never-ending animation I had set up. Whenever the app was suspended (such as when you multitask and open another app), on relaunching the app the animation was frozen. After some investigating, I discovered that with Core Animation you need to set a flag on the CABasicAnimation class called removedOnCompletion to NO otherwise the animation will get cleaned up when it gets suspended.

Objective-C:

CABasicAnimation *dartWiggleAnimation = [CABasicAnimation animationWithKeyPath:@"position"];
dartWiggleAnimation.fromValue =
   [NSValue valueWithCGPoint:CGPointMake(self.center.x-DART_WIGGLE_HALF, self.center.y+DART_CENTER_H_OFFSET)];
dartWiggleAnimation.toValue =
   [NSValue valueWithCGPoint:CGPointMake(self.center.x+DART_WIGGLE_HALF, self.center.y+DART_CENTER_H_OFFSET)];
dartWiggleAnimation.timingFunction =
   [CAMediaTimingFunction functionWithName: kCAMediaTimingFunctionEaseInEaseOut]; 
dartWiggleAnimation.duration = 0.4;
dartWiggleAnimation.repeatCount = HUGE_VALF;
dartWiggleAnimation.autoreverses = YES;
dartWiggleAnimation.removedOnCompletion = NO;
[[nextDart layer] addAnimation:dartWiggleAnimation forKey:@"dartWiggle"];

Swift:


        let dartWiggleAnimation = CABasicAnimation(keyPath: #keyPath(CALayer.position))
        dartWiggleAnimation.fromValue = CGPoint(x: self.center.x - DART_WIGGLE_HALF, y: self.center.y + DART_CENTER_H_OFFSET)
        dartWiggleAnimation.toValue = CGPoint(x: self.center.x + DART_WIGGLE_HALF, y: self.center.y + DART_CENTER_H_OFFSET)
        dartWiggleAnimation.timingFunction = CAMediaTimingFunction(name: CAMediaTimingFunctionName.easeInEaseOut)
        dartWiggleAnimation.duration = 0.4
        dartWiggleAnimation.repeatCount = Float.greatestFiniteMagnitude
        dartWiggleAnimation.autoreverses = true
        dartWiggleAnimation.isRemovedOnCompletion = false
        nextDart.layer.add(dartWiggleAnimation, forKey: "dartWiggle")

Does this seem like a bug or a feature?

WWDC Update: 5 key points for iPhone apps

It’s now been just over 3 weeks since the torrent of information unleashed at Apple’s World Wide Developer Conference refreshingly drenched the brains of designers, developers and engineers. I’ve resisted blogging about the public announcements to fully let the impact soak in and gage everyone’s reactions but now feels like a good time to talk about where the future of computing is heading.
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The eve of Apple’s World Wide Developer Conference 2011

I’m writing this in a hotel room from a block adjacent from the Moscone West Conference center, here in San Francisco, CA. The atmosphere is incredibly lively and for many developers it’s as close to the developer-version of Christmas you can get. Ha ok I know that sounds a bit over the top but there is lots of optimism about Steve Jobs’ keynote tomorrow. You can feel it!

So today I picked up my WWDC attendee badge and hitched a ride on the small army of buses that Jeff LaMarche had arranged to go to Apple’s HQ in 1 Infinite Loop, Cupertino, CA. It’s such a historic place in tech history and I was there! Not only has it been the main home of Apple since Steve Jobs returned to Apple but also features on the front of the Google Map icon on every single iPhone, iPad and iPod Touch.

Me outside Apple HQ

I got my photo taken and chilled in the oddly named BJ’s bar opposite. I also visited the company store there and bought some Apple gear, I just need to work out how to fit the coffee mugs into my suitcase now! Just about to grab some food and chill in a bar with a number of other iPhone developers before getting an early night. Some people recommended getting up at 3am to get a good seat. Mmm, if only I hadn’t just tested out my new coffee mugs…

Calculating UNIX file permissions

Permissions Mac App A few years ago I wrote a simple but handy Mac app that calculates unix file permissions using a matrix of check boxes. I wrote it because I wanted to better understand how those octal values get calculated and to expand my experience of writing Mac apps.

I was also learning some crazy assembly code at the time too so I was also making sense of putting bitwise operations to task. Rather than let this code languish on my hard drive, I thought I’d share…
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