10 Commandments for iOS Software Development

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Ten Commandments for iOS Software Dev Adrian Kosmaczewski, akosma software

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http://www.ﬂickr.com/photos/gi/164281467/

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http://www.ﬂickr.com/photos/jm3/379494322/

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http://www.ﬂickr.com/photos/21025851@N00/2168398185/

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http://www.ﬂickr.com/photos/emiliagarassino/2146648332/

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akosma software

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akosma.com @akosmasoftware facebook.com/akosmasoftware

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Some questions

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Who’s new to iOS?

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Which technologies?

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J2EE J2ME .NET Ruby / Rails others?

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Which programming languages?

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C / C++? Java, C#? Ruby, Python, Lua? JavaScript? Fortran, Lisp, COBOL?

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10 Commandments

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http://www.ﬂickr.com/photos/oseillo/345879263/

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http://www.ﬂickr.com/photos/justdrew1985/4348527596/

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Thou shalt manage memory properly

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http://www.ﬂickr.com/photos/blakespot/3030107382/

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• iPhone and iPhone 3G: 128 MB RAM • iPhone 3GS and iPad 1: 256 MB RAM • iPhone 4, 4S and iPad 2: 512 MB RAM

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> 70 MB for the OS!

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no swap ﬁle

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(no virtual memory)

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http://www.ﬂickr.com/photos/cheek/699407283/

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no garbage collection

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objects have a “retain count”

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http://cocoadevcentral.com/d/learn_objectivec/

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basic rule:

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for every [alloc], [retain], [copy] there must be a [release]

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beware:

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Objective-C only allows objects on the heap

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http://linguiniontheceiling.blogspot.com/2008/10/thats-madame-trash-heap-to-you.html

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No automatic objects on the stack (C++)

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http://www.futuregov.net/photologue/photo/2008/aug/30/stack-papers/

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// C++ // Memory freed when out of scope std::string name(“Adrian”); std::string *name = NULL; name = new std::string(“Adrian”); delete name;

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iPhone OS memory warnings

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http://www.ﬂickr.com/photos/tbuser/2763035540/

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http://akosma.com/2009/01/28/10-iphone-memory-management-tips/

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Thou shalt remove all compiler warnings

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GCC_TREAT_WARNINGS_AS_ERRORS -Werror

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Why Warnings?

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• Using deprecated symbols; • Calling method names not declared in included headers; • Calling methods belonging to implicit protocols; • Forgetting to return a result in methods not returning “void”; • Forgetting to #import the header ﬁle of a class declared as a forward “@class”; • Downcasting values and pointers implicitly.

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Solutions

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Make your intentions explicit to the compiler

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• Make implicit protocols explicit • Create categories for private methods • Turn implicit type conversions and casts into explicit ones • Use @class in the @interface, #import on the @implementation

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http://akosma.com/2009/07/16/objective-c-compiler-warnings/

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Honor the Human Interface Guidelines

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http://developer.apple.com/iphone/ library/documentation/userexperience/ conceptual/mobilehig/

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Your Objective:

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avoid rejections

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http://ﬂyosity.com/application-design/iphone-application-design-patterns.php

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http://www.smashingmagazine.com/2009/07/21/iphone-apps-design-mistakes- overblown-visuals/

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http://www.mobileorchard.com/avoiding-iphone-app-rejection-from-apple/

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http://www.apprejected.com/

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http://appreview.tumblr.com/

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http://kosmaczewski.net/2009/08/03/risk-management-in-iphone-projects/

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Your Objective:

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avoid this

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http://www.ﬂickr.com/photos/gruber/2635257578/

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and this

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http://smokingapples.com/iphone/app-store-iphone/the-worst-twitter-client-ever/

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“ I can’t find one redeeming quality about this app. It’s slow to start [on a 3GS], doesn’t respond to taps while it’s trying to load other things, and crashes if you try to change modes a lot. It’s limited to only timeline, replies, and messages. It has no other functionality. Oh wait… I forgot its killer feature, you can have custom backgrounds and choose the color of your tweets. That totally makes up for its lack of useful features and sluggish performance. I’m not sure why someone would bother building such an inferior app other than that they wanted to find some suckers and score a quick buck. It seems even more insane to me that they’d be actively seeking out reviewers to cover this. I was given a promo code for ChillTwit, and even for free I didn’t want it on my phone. I was sad just from looking at screenshots. Actually seeing it running confirmed all of my fears. If it was a free app, I might forgive the developer, but the fact that he’s trying to get $0.99 out of people pisses me off to no end. Go buy Tweetie. If you somehow weren’t scared away by all my bitching and whinning, you can see ChillTwit on the app store here. But seriously, if you buy this, we’re not friends anymore.

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Thou shalt optimize for performance

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• Drawing and scrolling • Application launch • Files and data • Power and battery life

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Drawing and scrolling

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• UIView subclasses are already optimized • Custom views should use setNeedsDisplayInRect: whenever possible • Cache static objects

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• Use opaque views • Avoid allocating while scrolling • Reuse table cells • Collapse view hierarchies

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Application Launch

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• Design apps for quick launch and short use • Load data lazily • Load only images needed

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Files and Data

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• Use Core Data for large datasets • Avoid loading large ﬁles in memory • Use plist ﬁles for structured static data

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Power management

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• 3G communications are expensive • Wi-Fi slightly cheaper • Send small chunks of data at low frequency • Prefer “chunky” to “chatty” protocols • Better performance == longer battery life

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Thou shalt test in the device

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http://www.ﬂickr.com/photos/edans/1526393678/

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• Camera • Accelerometer • GPS • Compass • Battery • Network • ... Speed! http://www.ﬂickr.com/photos/tensafefrogs/728581345/

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http://www.ﬂickr.com/photos/schill/969088410/

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http://www.ﬂickr.com/photos/jaytamboli/3788327603/

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Keep your old iPhone 3G(S), 4, or iPod touches!

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http://en.wikipedia.org/wiki/File:3rareiphoneviews.jpg

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Thou shalt unleash the power of Instruments

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Instruments

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Thou shalt use PNG ﬁles

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Portable Network Graphics (PNG) is a bitmapped image format that employs lossless data compression. PNG was created to improve upon and replace GIF (Graphics Interchange Format) as an image-ﬁle format not requiring a patent license. It is pronounced /ˈpɪŋ/ [1] or spelled out as P-N-G. The PNG acronym is optionally recursive, unofﬁcially standing for “PNG's Not GIF”.[2] http://en.wikipedia.org/wiki/Portable_Network_Graphics

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Advantages

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Compression on build

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Low memory footprint

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Supported by all editors

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Quality

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http://en.wikipedia.org/wiki/File:Comparison_of_JPEG_and_PNG.png

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Transparency

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http://en.wikipedia.org/wiki/Portable_Network_Graphics

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• App icon: 57x57 “Icon.png” • Default image: 480x320 “Default.png” • Settings icon: 29x29 “Icon-Small.png”

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App Icon

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Design in maximum quality, then reduce

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Do not apply effects

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http://developer.apple.com/iphone/library/documentation/userexperience/conceptual/mobilehig/

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512x512 72 DPI TIFF ﬁle for App Store

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Thou shalt use static analysis

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http://llvm.org/

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http://clang-analyzer.llvm.org/

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Source: Apple Documentation

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Source: Apple Documentation

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Source: Apple Documentation

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Source: Apple Documentation

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Thou shalt care about accessibility

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Setting the accessibility properties in Xcode

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simple

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and there’s no reason not to do it.

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call to action!

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Add accessibility information to your apps now!

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Thou shalt have project management hygiene

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• Project management • Human resource management • Developer working conditions • Prototypes • Quality management • Code organization

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http://kosmaczewski.net/2009/07/28/code-organization-in-xcode-projects/

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Your objective:

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avoid chaos

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http://www1.standishgroup.com/newsroom/chaos_2009.php

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http://www.geekonomicsbook.com/

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Thou shalt have fun!

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and

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be creative!

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Recap’

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1. Manage memory properly 2. Remove compiler warnings 3. Read the Human Interface Guidelines 4. Optimize for performance 5. Test in the device

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6. Know your developer tools 7. Use PNG ﬁles 8. Use static analysis 9. Care about accessibility 10. Have project management hygiene