iPhone App: Windsock takes off

Windsock, my latest iPhone app is live in the App Store. It’s a clean, easy-to-use app that lets you check the wind forecast remotely and up to 4 days in advance. I built it because a hobby of mine is remote control plane flying but often there are days when the wind is too strong or in the wrong direction and packing the flight gear, driving down to the park only to find it is too windy to fly was frustrating (the plane has a wingspan of 56″ which is tricky to get out of a car at the best of times let alone when it is windy also strong wind is likely to make you lose control of your model and fly it into a tree or worse).

Instead I built this app to drop windsock markers down on a map and get the latest wind readings for a near-by location so I know if it’s great weather to fly. You can also save it as a site and with a quick glance see the best park or field to fly in. It is also iCloud ready so will sync your sites between devices and has a relative compass mode to help you discover the wind direction – beats throwing a bit of muddy grass in the air!

The app uses high resolution data to give high-resolution readings every 3 hours up to 5 days in advance. Tapping on the detail view within the app will condense the rows to give you a daily overview of the wind readings. I’ve tried to design it to work in two modes, the first mode is more of a quick overview so you can compare sites and decide the best one to go to, the other mode lets you drill down and view the forecast for a particular site.

It’s also a handy app if you do other outdoor activities, such as kitesurfing, windsurfing, paragliding, kite flying or just fly model planes. Please check it out on the App’s website or on the App Store.

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?

Reverting your library from a beta of iTunes

As an iPhone and iPad developer, Apple often present you with beta versions to install which sometimes require you to also install a beta version of iTunes. Of course the contents of these beta versions are under strict non-disclosure agreements but the process of rolling back isn’t so I’ll quickly explain how to do it…

When you installed the beta, it will upgrade your iTunes library database but if you try to downgrade back to the old version at a later date you’ll be presented with an error message saying that iTunes cannot read your library.

Don’t panic! The beta version has just moved your library database to a backup folder and with a simple drag and drop you can have your old library database up and running again. Your old database should be found in ~/Music/iTunes/Previous iTunes Libraries dated with when you upgraded. Just drag that back into ~/Music/iTunes renaming it to iTunes Library.itl (you’ll probably need to delete the existing iTunes Library.itl file too as that belonged to the beta version and you just uninstalled that).

That’s all you need to do to get your old iTunes library working again. Just before you begin make sure you back up everything!

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.
Continue reading →