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Everything in your iOS app happens on “the main thread” by default. It’s like at the hairdresser’s – one thing after another. Since iOS 4 however you can execute things “asynchronously” by using Grand Central Dispatch. With it comes another phenomenon called Blocks. To make use of this feature you need to define your own […]

Say you had the URL to a file on the web and you’d like to save said file in the app’s Documents directory. I thought it would be as simple as using the NSFilemanager and copying the URL. But it’s a little more complex than that. Instead, we can use NSData to retrieve the data […]

We can use NSData’s length method for this. Imagine your UIImage is yourImage: NSData *imageData = UIImageJPEGRepresentation(yourImage, 1); NSLog(@”Size of your image is %d bytes”, [imageData length]) [imageData length] returns a double in bytes, which will be the size of your image. This is useful if you’d like to save something and you’re limited in […]

You can query the NSFoundationVersionNumber like so: if (floor(NSFoundationVersionNumber) <= NSFoundationVersionNumber_iOS_6_1) { // you’re running iOS 6.1 or earlier } else { // you’re running iOS 7 or later } Note that if you’re compiling with an older SDK, the value you’re querying may not be defined – in which case, you must define it […]

Before the addition of 64bit in iOS it was possible to take an NSUInteger (or NSInteger) and put it into an int variable, like so: int arrayCount = [self.myArray count]; If you add 64bit support to your app you may notice a compiler warning when you do this: Implicit conversion loses integer precision: ‘NSInteger’ (aka […]

Since iOS 7 and OS X 10.9 the default journalling mode in SQLite Stores is WAL. In addition to the main store file you’ll find a WAL file with the same (or larger) size as the store file, and a less important SHM file. Prior to this implementation it was easy to save the context, […]