The Foundation Framework Provides Basic System Services for All Apps

Your apps, as well as UIKit and other frameworks, are built on the Foundation framework infrastructure. The Foundation framework provides many primitive object classes and data types, making it fundamental to app development. It also establishes conventions (for tasks such as deallocation) that make your code more consistent and reusable.

Use Foundation to:

• Create and manage collections, such as arrays and dictionaries

• Access images and other resources stored in your app

• Create and manage strings

• Post and observe notifications

• Create date and time objects

• Automatically discover devices on IP networks

• Manipulate URL streams

• Execute code asynchronously

You already used the Foundation framework in Your First iOS App. For example, you used an instance of the NSString class to store the user’s input in userName. You also used the Foundation instance method initWithFormat: to create the greeting string.

The UIKit Framework Provides Classes to Create a Touch-Based User Interface

All iOS apps are based on UIKit. You can’t ship an app without this framework. UIKit provides the infrastructure for drawing to the screen, handling events, and creating common user interface elements. UIKit also organizes a complex app by managing the content that is displayed onscreen.

Use UIKit to:

• Construct and manage your user interface

• Handle touch- and motion-based events

• Present text and web content

• Optimize your app for multitasking

• Create custom user interface elements

In Your First iOS App, you used UIKit. When you examined how an app starts up, you saw that the UIApplicationMain function creates an instance of the UIApplication class, which handles incoming user events. You implemented the UITextFieldDelegate protocol in order to dismiss the keyboard when the user taps the Done key. In fact, you used UIKit to create your entire interface with the UITextField, UILabel, and UIButton classes.

The Core Data Framework Manages the Data Model of an App

Core Data manages object-graphs. With Core Data, you create model objects, known as managed objects. You manage relationships between those objects and make changes to the data through the framework. Core Data takes advantage of the built-in SQLite technology to store and manage data efficiently.

Use Core Data to:

• Save and retrieve objects from storage

• Support basic undo/redo

• Validate property values automatically

• Filter, group, and organize data in memory

• Manage results in a table view with NSFetchedResultsController

• Support document-based applications

The Core Graphics Framework Helps You Create Graphics

High-quality graphics are an important part of all iOS apps. The simplest and most efficient way to create graphics in iOS is to use prerendered images with the standard views and controls of the UIKit framework and to let iOS do the drawing. UIKit also provides classes for custom drawing—including paths, colors, patterns, gradients, images, text, and transformations. Use UIKit, a higher-level framework, instead of Core Graphics, a lower-level framework, whenever possible.

Use Core Graphics when you want to write drawing code that you share directly between iOS and OS X. The Core Graphics framework, also known as Quartz, is nearly identical on both platforms.

Use Core Graphics to:

• Make path-based drawings

• Use antialiased rendering

• Add gradients, images, and colors

• Use coordinate-space transformations

• Create, display, and parse PDF documents

Core Animation Allows You to Make Advanced Animations and Visual Effects

UIKit provides animations that are built on top of the Core Animation technology. If you need advanced animations beyond the capabilities of UIKit, you can use Core Animation directly. The Core Animation interfaces are contained in the Quartz Core framework. With Core Animation, you create a hierarchy of layer objects that you manipulate, rotate, scale, transform, and so forth. By using Core Animation’s familiar viewlike abstraction, you can create dynamic user interfaces without having to use low-level graphics APIs such as OpenGL ES.

Use Core Animation to:

• Create custom animations

• Add timing functions to graphics

• Support key frame animation

• Specify graphical layout constraints

• Group multiple-layer changes into an atomic update

The OpenGL ES Framework Provides Tools for 2D and 3D Drawing

OpenGL ES supports basic 2D and 3D drawing. Apple’s implementation of the OpenGL ES standard works closely with the device hardware to provide high frame rates for full-screen game-style applications.

Use OpenGL ES to:

• Create 2D and 3D graphics

• Make more complex graphics, such as data visualization, flight simulation, or video games

• Access underlying graphics hardware