bolot

Software Engineer & Instructor at Big Nerd Ranch Europe, Taidoka, Photographer

[bolot]

what's id*?

My former Beginning iOS student asked me over email, "What's id*?" The answer seemed obvious and his first attempt at answering his own question was in the right direction, but as I started digging deeper, I realized that things aren't as simple as they seem. To answer the question more fully, I wrote a post that's published on the Big Nerd Ranch blog: Monsters from the id. I lift the curtain on how id is defined, look at the differences between NSObject * and id, talk about __autoreleasing variables and classes that do not inherit from the NSObject hierarchy.

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Coding Guidelines

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.

So, study the coding guidelines, learn to speak the "native language", and enjoy producing fantastic applications, which you won't be afraid to maintain once they become mega-hits on the App Store.

[bolot]

Duplicate bug report

Received an email from Apple yesterday informing me that my bug has been closed as a duplicate. Woohoo! This means that somebody else had reported the same bug (rdar://12099514) and that my bug report counts as a "vote" to indicate that this one is important.

[bolot]

Xcode crashes on incrementing number of segments

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

At this point, Xcode will crash. It seems to be related to autolayout and I'm not yet sure if the Map view plays a role. I filed a bug report rdar://12546251. It looks like the bug happens only when editing XIB files, at least I wasn't able to reproduce it with storyboards yet.

[bolot]

Big Nerd Ranch in Amsterdam, Sept 2012

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 

Touch screens are indispensable for modern smartphones. However, they contain many other sensors that could greatly enrich the user experience. Learn how to tame Core Motion, measure attitude (yaw, pitch, and roll), and put them to good use in your mobile apps. iOS programming experience is required. Bring your own laptop with Mac OS X 10.7 or 10.8, Xcode 4.4, iOS 5 SDK, and membership in the iOS developer program (to allow running apps on the device). This guru session will be led by Mikey Ward, with Bolot Kerimbaev and Stijn Oomes assisting.

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Xcode code completion surprises

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; 

The choice of methods to implement depends on the requirements: is it an ordered or an unordered collection, is it mutable or immutable, etc. For more information, check Collection Accessor Patterns for To-Many Properties.

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Further reading for iOS bootcamp graduates

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.

Some arguments against developing non-native mobile apps: Shell Apps vs Native Apps (sandofsky.com) Why you should stay away from Appcelerator's Titanium (usingimho.wordpress.com)

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Controlling iOS Simulator with AppleScript

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

Note that it's important to capitalize "H", otherwise you'll end up hiding your simulator. It's the difference between cmd-shift-h and cmd-h.

[bolot]

Scene Kit Gotchas

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:

[SCNTransaction begin]; [SCNTransaction setDisableActions:NO]; [SCNTransaction setAnimationDuration:2.0]; [SCNTransaction setCompletionBlock:^{   CAKeyframeAnimation *anim = [self rotatAnim];   [cameraNode addAnimation:anim forKey:@"rotate"]; }]; cameraNode.position = SCNVector3Make(xCam, yCam, zCam); [SCNTransaction commit];