Inside Cocoa Touch : Exploring the iOS Technology Layers

9/14/2010 5:07:43 PM
Apple describes the technologies implemented within the iOS as a series of layers, with each layer being made up of different frameworks that can be used in your applications. As you might expect, the Cocoa Touch layer is at the top (see Figure 1).
Figure 1. The technology layers that make up the iOS.

Let’s review some of the most important frameworks that make up each of the layers. If you want a comprehensive guide to all frameworks, just search for each layer by its name in the Apple Xcode documentation.

By the Way

Apple has included three important frameworks in every iOS application template (CoreGraphics, Foundation, and UIKit). These frameworks are all that is needed for simple iOS applications and will cover most of what you do in this book. When additional frameworks are needed, I describe how to include them in your projects.

The Cocoa Touch Layer

The Cocoa Touch layer is made up of several frameworks that will provide the core functionality for your applications – including multitasking and advertising in iOS 4.x. UIKit could be described as the “rock star"—delivering much more than the UI in its name implies.


UIKit covers a wide range of functionality. It is responsible for application launching and termination, controlling the interface and multitouch events, and providing access to common views of data (including web pages and Word and Excel documents, among others).

UIKit is also responsible for many intra-iPhone integration features. Accessing the Media Library, Photo Library, and accelerometer is also accomplished using the classes and methods within UIKit.

Map Kit

The Map Kit framework enables developers to add Google Map views to any application, including annotation, location, and event-handling features.

Game Kit

The Game Kit framework adds network-interactivity to iPhone applications. Game Kit supplies mechanisms for creating and using peer-to-peer networks, including session discovery, mediation, and voice chat. These features can be added to any application, game or not!

Message UI/Address Book UI

Apple is sensitive to the need for integration between iOS applications. The Message UI and Address Book UI frameworks can be used to enable email composition and contact access from any application you develop.


The iAd framework supports the addition of ads to your applications. iAds are interactive advertising pieces that can be added to your software with a simple drag and drop. You do not need to manage iAds interactions in your application – Apple does this for you.

The Media Layer

When Apple makes a computing device, you’d better believe that they put some thought into the media capabilities. The iPhone can create complex graphics, play back audio and video, and even generate real-time 3D graphics. The Media layer’s frameworks handle it all.

AV Foundation Framework

The AV Foundation Framework can be used to managing complex sound and video playback and editing. This should be used for implementing advanced features, such as movie recording, track management, and audio panning.

Core Audio

The Core Audio framework exposes methods for handling basic playback and recording of audio on the iPhone. It includes the AudioToolbox framework, which can be used for playing alert sounds or generating short vibrations, and the AudioUnit.framework for processing sounds.

Core Graphics

Use the Core Graphics framework to add 2D drawing and compositing features to your applications. Although most of this book will use existing interface classes and images in its applications, you can use core graphics to programmatically manipulate the iPhone’s view.

Core Text

Provides precise positioning and control over text that is displayed on the iPhone screen. Core Text should be used in mobile text-processing applications and software that requires high-quality and fast presentation and manipulation of styled text.

Image I/O

The Image I/O framework can be used to import and export both image data and image metadata for any file format supported by iOS.

Media Player

The Media Player framework provides you, the developer, with an easy way to play back movies with typical onscreen controls. The player can be invoked directly from your application.


OpenGL ES is a subset of the popular OpenGL framework for embedded systems (ES). OpenGL ES can be used to create 2D and 3D animation on the iPhone. Using OpenGL requires additional development experience beyond Objective-C, but can generate amazing scenes for a handheld device—similar to what is possible on modern game consoles.

Quartz Core

The Quartz Core framework is used to create animations that will take advantage of the hardware capabilities of your iPhone. This includes the feature set known as Core Animation.

The Core Services Layer

The Core Services layer is used to access lower-level operating system services, such as file access, networking, and many common data object types. You’ll make use of core services frequently by way of the Foundation framework.

Address Book

The Address Book framework is used to directly access and manipulate address book information. This is used to update contact information and/or use it within your applications.


The CFNetwork framework provides access to BSD sockets, HTTP and FTP requests, and Bonjour discovery.

Core Data

The Core Data framework can be used to create the data model of an iOS application. Core Data provides a relational data model based on SQLite, and can be used to bind data to interface objects to eliminate the need for complex data manipulations in code.

Core Foundation

Core Foundation provides much of the same functionality of the Foundation framework, but is a procedural C framework, and therefore requires a different development approach that is, arguably, less efficient than Objective-C’s object-oriented model. You should probably avoid Core Foundation unless you absolutely need it.


The Foundation framework provides an Objective-C wrapper around features in Core Foundation. Manipulation of strings, arrays, and dictionaries is handled through the Foundation framework, as are other fundamental application necessities, including managing application preferences, threads, and internationalization.

Event Kit

The Event Kit framework be used to access calendar information stored on the iOS device. It also enables the developer to create new events within a calendar, including alarms.

Core Location

The Core Location framework can be used to obtain latitude and longitude information from the iPhone’s GPS (WiFi-based location service in the original iPhone) along with a measurement of precision.

Core Motion

The Core Motion framework manages most motion-related events on the iOS platform, such as using the accelerometer or the new gyroscope of the iPhone 4. Core Motion is new to iOS 4, but the features have been available in earlier versions of the OS.

Quick Look

The Quick Look framework implements file viewing within an application, even if the application does not “know” how to open a specific file type. This is intended for viewing files downloaded to the device.

Store Kit

The Store Kit framework enables developers to create in-application transactions for purchasing content without exiting the software. All interactions take place through the App Store, so no financial data is requested or transmitted through the Store Kit methods.

System Configuration

Use the System Configuration framework to determine the current state of the iPhone’s network configuration—what network it is connected to (if any) and what devices are reachable.

The Core OS Layer

The Core OS layer, as you’d expect, is made up of the lowest-level services in the iOS. These features include threads, complex math, hardware accessories, and cryptography. You should only need to access these frameworks in rare circumstances.


The Accelerate framework simplifies complete calculations and large-number manipulation. This includes digital signal processing capabilities.

External Accessory

The External Accessory framework is used to develop interfaces to accessories connected via the dock connector or Bluetooth.


The Security framework provides functions for performing cryptographic functions (encrypting/decrypting data). This includes interacting with the iOS keychain to add, delete, and modify items.


The System framework gives developers access to a subset of the typical tools they would find in an unrestricted UNIX development environment.

  •  The Language of Apple Platforms : Memory Management
  •  The Language of Apple Platforms : Objective-C Programming Basics
  •  The Language of Apple Platforms : Exploring the Objective-C File Structure
  •  The Language of Apple Platforms : Object-Oriented Programming and Objective-C
  •  Using the iPhone Simulator
  •  Introduction to Xcode Simulator
  •  Creating a Development Provisioning Profile on iPhone
  •  Preparing Your System and iPhone for Development
  •  Understanding Mobile Networking and Remote Access in Vista
  •  Creating Connections for Remote Access in Vista
  •  Configuring Mobile Connection Properties in Vista
  •  Establishing Mobile Connections in Vista
  •  Wireless Networking in Vista
  •  Configuring Power Management Settings in Vista
  •  Configuring Networking for Laptops
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  •  Mobile Commerce Applications, Part 1
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