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CHAPTER 1 : INTRODUCTION
Cocoa is an application environment for both the Mac OS X operating system and iPhone OS, the operating system used on multi-touch devices such as iPhone and iPod touch. It consists of a suite of object-oriented software libraries, a runtime, and an integrated development environment
The Cocoa Environment
Cocoa is a set of object-oriented frameworks that provides a runtime environment for applications running on Mac OS X and iPhone OS. It is also part of a development environment that helps you efficiently bring these applications from design stage to deployment. Cocoa is the preeminent application environment for Mac OS X and the only application environment for iPhone OS. (Carbon is an alternative environment on Mac
OS X, but it is a compatibility framework with procedural programmatic interface intended to support existing Mac OS X code bases.) Most of the applications you see on Mac OS X and iPhone OS, including Mail and Safari, are Cocoa applications. An integrated development environment called Xcode supports application development for both platforms. The combination of this development environment and Cocoa makes it easy to create a well-factored, full-featured application.
Introducing Cocoa
As with all application environments, Cocoa presents two faces; it has a runtime aspect and a development aspect. In its runtime aspect, Cocoa applications present the user inter face and are tightly integrated with the other visible portions of the operating system; on Mac OS X, these include the Finder, the Dock, and other applications from all environments. But it is the development aspect that is the more interesting one to programmers. Cocoa is an integrated suite of object-oriented software components—classes—that enables you to rapidly create robust, full-featured Mac OS X applications. These classes are reusable and adaptable software building blocks; you can use them as-is or extend them for your specific requirements. Cocoa classes exist for just about every conceivable development necessity, from user-inter face objects to data formatting, and where a need hasn’t been anticipated, you can easily create a subclass of an existing class that answers that need.
Cocoa history
Cocoa is the continuation of several frameworks (primarily the App Kit and Foundation Kit) from the NeXTSTEP and OPENSTEP programming environments developed by NeXT in the 1980s and 1990s. Apple acquired NeXT in December 1996, and subsequently went to work on the Rhapsody operating system that was supposed to be the direct successor of OPENSTEP. It was to have had an emulation base for Mac OS applications, called Blue Box. The OPENSTEP base of libraries and binary support was termed Yellow Box. Rhapsody evolved into Mac OS X, and the Yellow Box became Cocoa. As a result, Cocoa classes begin with the acronym "NS" (standing either for the NeXT-Sun creation of OPENSTEP, or for the
original proprietary term for the OPENSTEP framework, NeXTSTEP): NSString, NSArray, etc. Much of the work that went into developing OPENSTEP was applied to the development of Mac OS X, Cocoa being the most visible part. There are, however, some differences. For example, NeXTSTEP and OPENSTEP used Display PostScript for on-screen display of text and graphics, while Cocoa depends on Apple's Quartz (which uses the PDF imaging model). Cocoa also has a level of Internet support, including the NSURL and WebKit HTML classes, and others, while under OPENSTEP there was only rudimentary support for managed network connections through NSFileHandle classes and Berkeley sockets.
Prior to its current use, the "Cocoa" trademark was the name of an application that allowed children to create multimedia projects. It was originally known as KidSim, and is now licensed to a third party and marketed as Stagecast Creator. The program was discontinued in one of the rationalizations that followed Steve Jobs' return to Apple. The name was re-used to avoid the delay while registering a new trademark, with Stagecast agreeing to market the older Cocoa under a new name.

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CHAPTER 1 : INTRODUCTION
Cocoa is an application environment for both the Mac OS X operating system and iPhone OS, the operating system used on multi-touch devices such as iPhone and iPod touch. It consists of a suite of object-oriented software libraries, a runtime, and an integrated development environment
The Cocoa Environment
Cocoa is a set of object-oriented frameworks that provides a runtime environment for applications running on Mac OS X and iPhone OS. It is also part of a development environment that helps you efficiently bring these applications from design stage to deployment. Cocoa is the preeminent application environment for Mac OS X and the only application environment for iPhone OS. (Carbon is an alternative environment on Mac
OS X, but it is a compatibility framework with procedural programmatic interface intended to support existing Mac OS X code bases.) Most of the applications you see on Mac OS X and iPhone OS, including Mail and Safari, are Cocoa applications. An integrated development environment called Xcode supports application development for both platforms. The combination of this development environment and Cocoa makes it easy to create a well-factored, full-featured application.
Introducing Cocoa
As with all application environments, Cocoa presents two faces; it has a runtime aspect and a development aspect. In its runtime aspect, Cocoa applications present the user inter face and are tightly integrated with the other visible portions of the operating system; on Mac OS X, these include the Finder, the Dock, and other applications from all environments. But it is the development aspect that is the more interesting one to programmers. Cocoa is an integrated suite of object-oriented software components—classes—that enables you to rapidly create robust, full-featured Mac OS X applications. These classes are reusable and adaptable software building blocks; you can use them as-is or extend them for your specific requirements. Cocoa classes exist for just about every conceivable development necessity, from user-inter face objects to data formatting, and where a need hasn’t been anticipated, you can easily create a subclass of an existing class that answers that need.
Cocoa history
Cocoa is the continuation of several frameworks (primarily the App Kit and Foundation Kit) from the NeXTSTEP and OPENSTEP programming environments developed by NeXT in the 1980s and 1990s. Apple acquired NeXT in December 1996, and subsequently went to work on the Rhapsody operating system that was supposed to be the direct successor of OPENSTEP. It was to have had an emulation base for Mac OS applications, called Blue Box. The OPENSTEP base of libraries and binary support was termed Yellow Box. Rhapsody evolved into Mac OS X, and the Yellow Box became Cocoa. As a result, Cocoa classes begin with the acronym "NS" (standing either for the NeXT-Sun creation of OPENSTEP, or for the
original proprietary term for the OPENSTEP framework, NeXTSTEP): NSString, NSArray, etc. Much of the work that went into developing OPENSTEP was applied to the development of Mac OS X, Cocoa being the most visible part. There are, however, some differences. For example, NeXTSTEP and OPENSTEP used Display PostScript for on-screen display of text and graphics, while Cocoa depends on Apple's Quartz (which uses the PDF imaging model). Cocoa also has a level of Internet support, including the NSURL and WebKit HTML classes, and others, while under OPENSTEP there was only rudimentary support for managed network connections through NSFileHandle classes and Berkeley sockets.
Prior to its current use, the "Cocoa" trademark was the name of an application that allowed children to create multimedia projects. It was originally known as KidSim, and is now licensed to a third party and marketed as Stagecast Creator. The program was discontinued in one of the rationalizations that followed Steve Jobs' return to Apple. The name was re-used to avoid the delay while registering a new trademark, with Stagecast agreeing to market the older Cocoa under a new name.
How Cocoa Fits into Mac OS X
Figure1-1shows a simplified diagram of the Mac OS X system architecture.
Figure1-1 Mac OS X architecture—simplified perspective
This diagram is simple for a purpose: to depict unambiguously to those unfamiliar with Mac OS X some of its major components and dependencies. But in its simplicity it omits important details and blurs others. These details fill in an important part of the picture showing how Cocoa fits into the rest of Mac OS X.
Figure 1-2 situates Cocoa more accurately in an architectural setting. This diagram shows Mac OS X as a series of software layers going from the foundation of Darwin to the various application environments; the intervening layers represent the system software contained in the two major umbrella frameworks, Core Services and Application Services. The diagram suggests that a component at one layer generally has dependencies on the layer beneath it.
Figure1-2 Cocoa in the architecture of Mac OSX
Features of a Cocoa Application
It is possible to create a Cocoa application without adding a single line of code. Make a new Cocoa application project using Xcode and then build the project. That’s it. Of course, this application won’t do much, or at least much that’s interesting. But this extremely simple application still launches when double-clicked, displays its icon in the Dock, displays its main menu and window (entitled “Window”), hides itself on command, behaves nicely with other running applications, and quits on command. You can move, resize, minimize, and close the window. You can even print the emptiness contained by the window.
• Basic application framework—Cocoa provides the infrastructure for event-driven behavior and for application-, window-, and workspace-management. In most cases, you won’t have to handle events directly or send any drawing commands to a rendering library.
• User-interface objects—Cocoa offers a rich collection of ready-made objects for your application’s user interface. Most of these objects are available on palettes of Interface Builder, a development application for creating user interfaces; you simply drag an object from a palette onto the surface of your interface, configure its attributes, and connect it to other objects. (And, of course, you can always instantiate, configure, and connect these objects programmatically.) Here is a sampling of Cocoa user-interface objects:.
In addition, Cocoa features technologies that support user interfaces, including those that promote accessibility, perform validation, and facilitate the connections between objects in the user interface and custom objects.
• Drawing and imaging—Cocoa enables efficient drawing of custom views with a framework for locking graphical focus and marking views (or portions of views) as “dirty.” It includes programmatic tools for drawing Bezier paths, performing affine transforms, compositing images, and creating various representations of images.
• System interaction—Cocoa gives your application ways to interact with (and use the services of) the file system, the workspace, and other applications.
• Data exchange—Cocoa simplifies the exchange of data within an application and between applications using the copy-paste and drag-and-drop models and through the Services menu.
• Performance—To enhance the performance of your application, Cocoa provides programmatic support for multithreading, idle-time processing, lazy loading of resources, memory management, and run-loop manipulation.
• Document-based applications—Cocoa specifies an architecture for applications composed of a potentially unlimited number of documents, with each contained in its own window (a word processor, for example). Indeed, if you choose the “Document-based application” project type, many of the components of this sort of application are created for you.