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Talk about serendipity. My friend Samuel Goodwin and I were discussing the importance of coding standards last weekend and this Monday morning I received an email from one of my students asking for recommendations on just this topic. Luckily, Apple has created documentation that covers it well: Coding Guidelines (developer.apple.com) include suggestions on acceptable and preferred naming conventions. While there, also take a look at Cocoa Design Patterns (developer.apple.com).

So, why would you want to follow coding guidelines? Isn't it usually something that developers in large organizations need? What about independent freelancers?

As a software developer, you will likely collaborate with others, even when working on your own project. At the very least, you will collaborate with one person: yourself in the future. Be kind to that girl or guy. What you're writing now may "get-the-job-done", be sufficiently clear, "good-enough", etc. However, will you still understand what you wrote two weeks from now? six months from now?

The coding guidelines help tremendously in this regard. Following generally accepted naming conventions can allow somebody to understand the purpose and meaning of various methods, functions, properties, classes, etc. Clarity and consistency will help somebody quickly learn the new API.

A good example is the UICollectionView in iOS 6. Even though it's brand new and introduces a slew of other supporting classes, it's easy to understand for somebody with iOS development experience. In many ways it is similar to UITableView: it follows the delegate and data source patterns, it reuses cell views, etc. So, while it introduces a lot of new functionality that didn't exist before, it is relatively easy to get up and running with it.

Yesterday, two of my students reported that Xcode crashes when they try to do one of the challenges in the Big Nerd Ranch iOS Programming book. They needed to add a segmented control to be able to switch between the types of maps. A single crash could possibly be dismissed as a fluke, but two, within minutes of each other? I decide to check it out and sure enough, I also had a crash in Xcode 4.5.1 (4G1004).

Here's how to reproduce the problem:

Create a single-view project, no storyboards.

Update the XIB as follows:

Drop a Map view (full screen)

Add an activity indicator, centered horizontally, standard distance from the top

Add a segmented control, centered horizontally, standard distance from the bottom

Increment the number of segments

Big Nerd Ranch is participating in a few interesting events in Amsterdam mid-September 2012:

First, we're part of the Appsterdam App Ecosystem Tent at the PICNIC'12 festival. Come see our talk Perpetuum Mobile: Myth or Revolution on Monday, September 17 at 15:00. Mikey Ward (@wookiee) is leading the guru session titled Beyond Touch: Attitudes in Motion on Tuesday, September 18 at 11:00.

Second, we're presenting a workshop for iOS and Mac developers together with Apple in the morning of Wednesday, September 19. Developers can register here. Follow @bignerdranch for additional announcements.

Here are the titles/abstracts of our PICNIC'12 presentation and guru session.

Perpetuum mobile: myth or revolution? Presentation 

Three quarters of the world population have access to mobile phones. The number of smartphones alone topped 1 billion. New uses of mobile technology offer hope in curing diseases and making the world a better place. Mobile devices empower users and app makers. But has the mobile revolution happened yet?

Beyond Touch: Attitudes in Motion Guru Session 

Code completion in Xcode saves time, it's (usually) your best friend. Your class complies with the UITableViewDataSource protocol? Start typing "dash-space-t-a-b-l-e" and you'll see a list of different methods that you can implement.

Similarly, start typing a method name that exists in the superclass and the completion will allow you to quickly enter the correct signature to override the method.

One of my students asked me a question about some confusing suggestions for methods that don't exist in any declared protocols or superclass(es). Let's say you define a property:

@property (nonatomic, strong) NSString *myPropertyName;

When you start typing a new method name, code completion will offer very strange code completion options, in addition to the usual suspects:

If you accept one of these (e.g., removeMyPropertyName:) and try to command-click on it, you'll be notified that the symbol is not found. What's going on? Turns out, most of these are related to Key-Value Coding, and specifically to Collection Accessor Patterns for To-Many Properties.

With collection accessor methods, it's possible to use classes other than NSArray and NSSet for implementing to-many relationships. These methods can improve design and performance, especially in case of mutable to-many relationships.

Here's the list of extra methods that will be suggested for the property myPropertyName:

- (void)addMyPropertyName:(NSSet *)objects; - (void)addMyPropertyNameObject:(object-type *)object; - (NSUInteger)countOfMyPropertyName; - (NSEnumerator *)enumeratorOfMyPropertyName; - (void)getMyPropertyName:(object-type **)buffer range:(NSRange)inRange; - (void)insertMyPropertyName:(NSArray *)array atIndexes:(NSIndexSet *)indexes; - (void)insertObject:(object-type *)object inMyPropertyNameAtIndex:(NSUInteger)index; - (void)intersectMyPropertyName:(NSSet *)objects; - (object-type *)memberOfMyPropertyName:(object-type *)object; - (NSArray *)myPropertyNameAtIndexes:(NSIndexSet *)indexes; - (id)objectInMyPropertyNameAtIndex:(NSInteger)index; - (void)removeMyPropertyName:(NSSet *)objects; - (void)removeMyPropertyNameAtIndexes:(NSIndexSet *)indexes; - (void)removeMyPropertyNameObject:(object-type *)object; - (void)replaceMyPropertyNameAtIndexes:(NSIndexSet *)indexes withMyPropertyName:(NSArray *)array; - (void)replaceObjectInMyPropertyNameAtIndex:(NSUInteger)index withObject:(id)object; 

While teaching one of the Big Nerd Ranch iOS bootcamps, I've compiled a list of articles for further reading for my students.

Explanation of the Cocoa initializer pattern: The How and Why of Cocoa Initializers (mikeash.com) What does it mean when you assign [super init] to self? (cocoawithlove.com)

Exploration of objc_msgSend() in Mac OS X Snow Leopard (friday.com)

Design Patterns: Key-Value Observing (cupsofcocoa.com)

A Motivation for ivar decorations (weblog.bignerdranch.com) Note that Xcode 4.4 adopts this convention by default and automatically treats properties as if they were synthesized with the backing variable prefixed by the underscore. Explicitly specifying @synthesize will override this default behavior. While you're on the BNR blog, read other articles.

One of my students asked if it were possible to rotate the iOS simulator from the command line. After a brief search, I ran into this stackoverflow hint to reset the iOS simulator using AppleScript, which I modified to rotate the simulator, instead. You can see the version I created during the class here.

However, it's possible it won't work for you. One, you have to enable access for assistive devices in System Preferences. Two, your Mac's language must be English, so that the menu titles match the script. The script assumes the menus are called "Hardware" and "Rotate Left". A few weeks ago I switched my Mac to Dutch, so while "Hardware" remains the same, the second one became "Roteer linksom".

So, to get around the language specificity, I came up with a simpler and more robust solution, using keyboard shortcuts:

tell application "iPhone Simulator" to activate tell application "System Events" to key code 123 using command down

Key code 123 is the left arrow key, key code 124 is the right arrow key. It's also possible to send other keyboard shortcuts, for example this script will simulate pressing the home button:

tell application "iPhone Simulator" to activate tell application "System Events" to keystroke "H" using command down

Scene Kit is a wonderful addition to OS X Mountain Lion, but it's good to be aware of some of its gotchas and limitations.

Scene Kit doesn't support animations based on CGPath

Scene Kit does not support animations based on CGPath, e.g., Bezier curves.

CAKeyframeAnimation *pathAnim = [CAKeyframeAnimation animationWithKeyPath:@"curve"]; CGPathRef path = [self makePath]; pathAnim.path = path; [sphereNode addAnimation:pathAnim forKey:@"path"];

Attempting to add a keyframe animation with the path property results in the following error messages:

CAKeyframeAnimation based on CGPath are not supported [SCNKit ERROR] Error while converting a CAAnimation to a SCNAnimation

Use SCNTransaction, not CATransaction

Chaining animations with CATransaction's completionBlock does not work. Instead, use SCNTransaction: