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This chapter is from the book

Understanding Model Differences

When it comes to application development, many iOS apps never have to consider the platform on which they’re being run. Most programs rely only on the display and touch input. They can be safely deployed to all the current family of iOS devices; they require no special programming or concern about which platform they are running on.

There are, however, real platform differences. The most obvious difference is in screen size between iPhones/iPod touches and iPads. Other differences are usually feature-based such as the types of sensors, the presence or absence of cellular-based networking, and a few other items.

These differences can play a role in deciding how you tell the App Store to sell your software and how you design the software in the first place. Should you deploy your software only to the iPhone family or only to the iPad? To the iPhone, the iPad, and the second-generation and later iPod touch? Or can your application be targeted to every platform? You can use APIs and other techniques to find out what particular features are on a given device and even enable or disable parts of your app. The next section covers some issues to consider.

Screen Size

The most obvious difference is the amount of screen space available on the iPad family versus iPhone or iPod touch. iPads have a large 1024x768 point resolution enabling the display of much more content. iPhones and iPod touches have two display geometries: The 3.5-inch screen used by earlier devices is 480x320 points while the newer 4-inch screen is 568x320.

Notice that the above resolutions are in points, not pixels. Most Apple devices now use a higher resolution retina display, doubling the number of available pixels and better matching human vision. Luckily, instead of worrying about whether the device is 480x320 (non-retina) pixels or 960x640 (retina) pixels, you can work in the world of points. For artwork, Xcode makes it easy to provide any appropriate resolutions and, at runtime, the system automatically chooses the right one.

The Apple human interface guidelines for iPad differ from those for iPhone/iPod touch. Developing for the iPad involves creating unified interfaces rather than the staged screen-by-screen design used by the earlier iPhone and iPod touch units, with their reduced window size. Applications that rely on the greater screen scope that the iPad provides may not translate well to the smaller members of the device family.

Although the retina screens on the newer iPhones and iPod touches look great, their screen dimensions are either 3.5- or 4-inches diagonal. That geometry, combined with the physical realities of the human hand and fingers, prevents these units from providing the same kind of user interaction experience that is possible on the iPad. The interaction guidelines for the newest units remain in lock step with the earlier members of the iPhone and iPod touch family.


Most applications can assume there will be at least one camera. In most cases, there will be front- and back-facing cameras, though it is still wise to check at runtime. Although some very early devices had no camera (earlier iPod touches or the first-generation iPad), those devices make up a very small percentage of the market, and none of them run iOS 7. There are also devices with just a back-facing or a front-facing camera. The 16GB fifth-generation iPod touch is an example of the latter.

The cameras are useful. You can have the camera take shots and then send them to Flickr or Twitter. You can use the camera to grab images for direct manipulation, augmented reality, and so forth. The iOS SDK provides a built-in image picker controller that offers camera access to your users. There are also ways to capture still images, capture video, play movies, and stream content.


All iOS devices have headphone jacks and all but the very oldest have speakers as well. The same is true of microphones. The SDK provides ways to capture and play back audio.

The microphones and speakers are also used for accessibility features such as the VoiceOver screen reader. You can build descriptions into your graphical user interface (GUI) elements to enable your applications to take advantage of VoiceOver, so your interfaces can describe themselves to visually impaired end users.


It may seem an overly obvious point to make, but the iPhone’s telephony system, which handles both phone calls and SMS messaging, can and will interrupt applications when the unit receives an incoming telephone call. Sure, users can suspend out of apps whenever they want on the iPhone, iPad, and iPod touch platforms, but only the iPhone has to deal with the kind of transition that’s forced by the system and not a choice by the user.

In addition to phone calls suspending your app, the user is able to open your app while on a call. When that happens, iOS adds a special top bar indicating the status of the call. Make sure to test your interface with the bar open as well as the bar being open then closing. The simulator lets you toggle the in-call status bar on and off.

Consider how the different kinds of interruptions might affect your application. It’s important to keep all kinds of possible exits in mind when designing software. Be aware that the choice to leave your app might not always come from the user, especially on the iPhone. Applications that use audio need to take special care to restore the correct state after phone call interruptions.

Another fallout of telephony operations is that more processes end up running in the background on iPhones than on iPod touches and iPads, even those iPads that provide cellular data support. These processes do reduce the amount of free memory, though for modern devices, the effect is minimal. Having said that, it still pays to test your app on cellular-enabled devices.

Core Location and Core Motion Differences

Core Location depends on three different approaches, each of which might or might not be available on a given platform. These approaches are limited by each device’s onboard capabilities. Wi-Fi location, which scans for local routers and uses their MAC addresses to search a central position database, is freely available on all iPhone, iPad, and iPod touch platforms.

Cell location, however, depends on an antenna that is available on the iPhone and on suitably equipped iPad models. This technology triangulates from local cell towers, whose positions are well defined from their installations by telephone companies.

The final and most accurate strategy, GPS location, depends on appropriate hardware. Most modern iPhones and iPads come with the hardware, though as of the writing of this book, no iPod touches do. You can use built-in calls to check for the presence of the hardware.

The third-generation iPhone 3GS introduced a built-in compass (via a magnetometer) along with the Core Location APIs to support it. The iPhone 4 and iPad 2 added a three-axis gyro, which provides pitch, roll, and yaw feedback, all of which can be solicited via the Core Motion framework. Most modern iPhone and iPad devices have both the compass and gyro. Modern iPod touches have only the gyro as of the writing of this book.

Vibration Support and Proximity

Vibration, which adds tactile feedback to many games, is limited to iPhones. The iPad and iPod touch do not offer vibration support. Nor do they include the proximity sensor that blanks the screen when holding an iPhone against your ear during calls. The UIDevice class offers direct access to the current state of the proximity sensor.

Processor Speeds

All modern devices come with fast Apple-designed ARM processors. The CPU includes a good amount of fast access RAM for code execution. To save power, some devices run the CPU at slower speeds (underclocked), and all have the ability to suspend parts of the hardware. Some earlier devices had relatively slow processors and much less execution space though they make up an ever-decreasing part of the market. Targeting iOS 6 or later will avoid those early devices.

The important thing is to run your app on a representative sample of the kinds of devices you are targeting. Make sure it performs well on the devices your customers will use. This is especially important if you plan to support iPhones prior to the 4 as well as first-generation iPads.

If your application isn’t responsive enough on the older platforms, consider working up your code efficiency. There is no option in the App Store at this time that lets you omit earlier generation iPhone devices from your distribution base, although setting your minimal required iOS version to 6.0 or higher will automatically exclude most older devices.

There are a few places you can look for an idea of the market share for each version of iOS. When a new version is released, check the Apple-oriented press, such as the following sites:

You can also check with data analysis and mobile information companies, though you might have to dig to find the information:

Finally, app developer David Smith regularly updates what OS versions are used in his app:


OpenGL ES offers a royalty-free cross-platform API for 2D- and 3D-graphics development. It is provided as part of the iOS SDK. Most devices support OpenGL ES 2.0 with the newest support version 3.0. Some very early units supported only OpenGL ES 1.1, but you are unlikely to encounter them.


One obvious difference is the version of iOS running on any given device. iOS device users are quick to upgrade to new releases. It took comparatively little time for most devices to upgrade from iOS 3 to 4, then 4 to 5, and 5 to 6. Although there are some models that cannot upgrade to iOS 7, they make up a rapidly shrinking percentage of the total number of units.

There are definitely differences in functionality between various versions of the OS. For example, in addition to the new look, iOS 7 introduces UI Motion, UI Dynamics, and Text Kit. All three offer ways to increase engagement with your user. Usually it is a decision of supporting the current version plus the one before—in this case, iOS 6 and 7. It is fairly easy to test for the availability of features and enable or disable access in your app. The largest difference is the user experience, though it is fairly easy to create interfaces that work on both 6 and 7 if you use the built-in UI elements.

Ultimately, what you support should depend on what your potential customers are using. If they are all using devices with iOS 7, there is no need to support 6. This book focuses on iOS 7, though with the exception of some specific features, everything will work in iOS 6. In addition, using auto layout, covered in Chapter 4, makes adapting your interfaces to each iOS much easier.

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