AppKit (formally Application Kit) is a

graphical user interface The GUI ( "UI" by itself is still usually pronounced . or ), graphical user interface, is a form of user interface that allows users to interact with electronic devices through graphical icons and audio indicator such as primary notation, inste ...

toolkit A toolkit is an assembly of tools; set of basic building units for user interfaces. The word toolkit may refer to: * Abstract Window Toolkit * Accessibility Toolkit * Adventure Game Toolkit * B-Toolkit * Battlefield Mod Development Toolkit * Ch ...

. It initially served as the UI framework for

NeXTSTEP NeXTSTEP is a discontinued object-oriented, multitasking operating system based on the Mach kernel and the UNIX-derived BSD. It was developed by NeXT Computer in the late 1980s and early 1990s and was initially used for its range of proprieta ...

. Along with

Foundation Foundation may refer to: * Foundation (nonprofit), a type of charitable organization ** Foundation (United States law), a type of charitable organization in the U.S. ** Private foundation, a charitable organization that, while serving a good cause ...

and

Display PostScript Display PostScript (or DPS) is a 2D graphics engine system for computers which uses the PostScript (PS) imaging model and language (originally developed for computer printing) to generate on-screen graphics. To the basic PS system, DPS adds a num ...

, it became one of the core parts of the

OpenStep OpenStep is a defunct object-oriented application programming interface (API) specification for a legacy object-oriented operating system, with the basic goal of offering a NeXTSTEP-like environment on non-NeXTSTEP operating systems. OpenStep was ...

specification of APIs. Later, AppKit and Foundation became part of

Cocoa Cocoa may refer to: Chocolate * Chocolate * ''Theobroma cacao'', the cocoa tree * Cocoa bean, seed of ''Theobroma cacao'' * Chocolate liquor, or cocoa liquor, pure, liquid chocolate extracted from the cocoa bean, including both cocoa butter and ...

, the

Objective-C Objective-C is a general-purpose, object-oriented programming language that adds Smalltalk-style messaging to the C programming language. Originally developed by Brad Cox and Tom Love in the early 1980s, it was selected by NeXT for its NeXTS ...

API framework of

macOS macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and lapt ...

GNUstep GNUstep is a free software implementation of the Cocoa (formerly OpenStep) Objective-C frameworks, widget toolkit, and application development tools for Unix-like operating systems and Microsoft Windows. It is part of the GNU Project. GNUstep ...

GNU GNU () is an extensive collection of free software (383 packages as of January 2022), which can be used as an operating system or can be used in parts with other operating systems. The use of the completed GNU tools led to the family of operat ...

's implementation of the OpenStep/Cocoa API, also contains an implementation of the AppKit API. AppKit comprises a collection of

classes and

protocols Protocol may refer to: Sociology and politics * Protocol (politics), a formal agreement between nation states * Protocol (diplomacy), the etiquette of diplomacy and affairs of state * Etiquette, a code of personal behavior Science and technology ...

that can be used to build an application in OpenStep/Cocoa. These classes can also be used in

Swift Swift or SWIFT most commonly refers to: * SWIFT, an international organization facilitating transactions between banks ** SWIFT code * Swift (programming language) * Swift (bird), a family of birds It may also refer to: Organizations * SWIFT, ...

through its Objective-C bridge.

Xcode Xcode is Apple's integrated development environment (IDE) for macOS, used to develop software for macOS, iOS, iPadOS, watchOS, and tvOS. It was initially released in late 2003; the latest stable release is version 14.2, released on December 13, ...

has built-in functionality for developing a Cocoa application using AppKit, including the ability to visually design user interfaces with

Interface Builder Interface Builder is a software development application for Apple Inc., Apple's macOS operating system. It is part of Xcode (formerly Project Builder), the Apple Developer developer's toolset. Interface Builder allows Cocoa (API), Cocoa and Car ...

. It relies heavily on patterns like

reference types In computer programming, data types can be divided into two categories: value types (or by-value types) and reference types (or by-reference types). Value types are completely represented by their meaning, while reference types are references to a ...

, delegation,

notifications Notification may refer to: * Notification (Holy See), an announcement by a department of the Roman Curia *Casualty notification, the process of notifying relatives of people who have been killed or seriously injured * Death notification, the proc ...

, target–action, and

model–view–controller Model–view–controller (MVC) is a software architectural pattern commonly used for developing user interfaces that divide the related program logic into three interconnected elements. This is done to separate internal representations of infor ...

. A sign of the NeXTSTEP heritage, AppKit's classes and protocols still use the "NS" prefix. Most of the applications bundled with macOS—for example, the Finder,

TextEdit TextEdit is an open-source word processor and text editor, first featured in NeXT's NeXTSTEP and OPENSTEP. It is now distributed with macOS since Apple Inc.'s acquisition of NeXT, and available as a GNUstep application for other Unix-like oper ...

Calendar A calendar is a system of organizing days. This is done by giving names to periods of time, typically days, weeks, months and years. A date is the designation of a single and specific day within such a system. A calendar is also a physi ...

, and

Preview Preview may refer to: Theatre, film, television * Preview (subscription service), an early subscription television service in the United States * Preview (theatre), a public performance of a theatrical show before the official opening * Previe ...

–use AppKit to provide their user interface.

iOS iOS (formerly iPhone OS) is a mobile operating system created and developed by Apple Inc. exclusively for its hardware. It is the operating system that powers many of the company's mobile devices, including the iPhone; the term also includes ...

iPadOS iPadOS is a mobile operating system developed by Apple Inc. for its iPad line of tablet computers. It is a rebranded variant of iOS, the operating system used by Apple's iPhones, renamed to reflect the diverging features of the two product l ...

, and

tvOS tvOS (formerly known as Apple TV Software) is an operating system developed by Apple Inc. for the Apple TV, a digital media player. In the first-generation Apple TV, Apple TV Software was based on Mac OS X. Starting with the second-generation ...

also support other UI frameworks, including

UIKit Cocoa Touch is the application development environment for building software programs to run on iOS for the iPhone and iPod Touch, iPadOS for the iPad, watchOS for the Apple Watch, and tvOS for the Apple TV, from Apple Inc. Cocoa Touch provid ...

, which is derived from AppKit and uses many similar structures, and SwiftUI, a

-only declarative UI framework. Prior to

macOS Catalina macOS Catalina (version 10.15) is the sixteenth major release of macOS, Apple Inc.'s desktop operating system for Macintosh computers. It is the successor to macOS Mojave and was announced at WWDC 2019 on June 3, 2019 and released to the publ ...

, macOS also supported

Carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...

, a UI framework derived from the

Macintosh Toolbox The Macintosh Toolbox implements many of the high-level features of the Classic Mac OS, including a set of application programming interfaces for software development on the platform. The Toolbox consists of a number of "managers," software compone ...

Classes

Of the more than 170 classes included in the Application Kit, the following classes form the core:AppKit Framework Reference
/ref> *NSApplication: a singleton object that represents the application as a whole and tracks its windows and other global state *NSWindow: an object representing a window on screen, it holds a hierarchy of views *NSView: an object representing a rectangular region; it may draw UI content of its own (using drawing engines like

Quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...

Core Animation Core Animation is an animation graphics compositing framework used by macOS (Mac OS X Leopard and later), iOS, watchOS, and tvOS to produce animated user interfaces. Overview Core Animation provides a way for developers to produce animated user i ...

, and

Metal A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...

), and it may also hold a subtree of other views *NSResponder: an object that can respond to events during the application's lifetime; NSApplication, NSWindow, and NSView are all subclasses of NSResponder *NSDocument: an object representing a document saved on disk that manages its display in a window *NSController: an

abstract class In programming languages, an abstract type is a type in a nominative type system that cannot be instantiated directly; a type that is not abstract – which ''can'' be instantiated – is called a ''concrete type''. Every instance of an abstra ...

implementing some functionality for a

controller Controller may refer to: Occupations * Controller or financial controller, or in government accounting comptroller, a senior accounting position * Controller, someone who performs agent handling in espionage * Air traffic controller, a person ...

, mediating between views and model objects

References

{{reflist

External links

AppKit classes, in OpenStep specification

Apple developer documentation for AppKit
NeXT MacOS Application programming interfaces

Classes

See also

References

External links