OS X Mountain Lion v10.8

This article summarizes the key technology changes and improvements available in OS X v10.8. The information about these changes is organized into sections by technology area.

For a detailed list of API changes, see OS X v10.8 API Diffs.

Please file any bug reports about this release or this documentation at http://bugreport.apple.com/.

Major Features

The following sections highlight OS X v10.8 features that span multiple technology areas or that are otherwise of particular importance to most developers.

Game Center

Game Center on OS X v10.8 accesses the same social-gaming network as on iOS, allowing users to track scores on a leaderboard, compare their in-game achievements, invite friends to play a game, and start a multiplayer game through automatic matching. Game Center functionality is provided in two parts:

  • The Game Center app, in which users sign in to their account, discover new games and new friends, add friends to their gaming network, and browse leaderboards and achievements.

  • The Game Kit framework, which contains the APIs developers use to support live multiplayer or turn-based games and adopt other Game Center features, such as in-game voice chat and leaderboard access.

Apple supports Game Center with the online Game Center service, which performs player authentication, provides leaderboard and achievement information, and handles invitations and automatching for multiplayer games. You interact with the Game Center service only indirectly, using the Game Kit APIs.

In your game, use the Game Kit APIs to post scores and achievements to the Game Center service and to display leaderboards in your user interface. You can also use Game Kit APIs to help users find others to play with in a multiplayer game.

To learn more about adding Game Center support to your app, see Game Center Programming Guide.

iCloud Enhancements

OS X v10.8 introduces the iCloud Document Library, which gives users an easy way to access the app-specific documents they’ve stored in iCloud. When users start an app that participates in iCloud storage, the iCloud Document Library appears and allows them to open, share, duplicate, and organize their documents.

If your app is NSDocument based, you can take advantage of the following things:

  • The iCloud Document Library view in the Open window

  • The appropriate menu items added to your app’s File menu and to a document’s Versions menu

  • A dialog that helps users resolve conflicts (when they open a document that they changed using another device)

To learn more about integrating iCloud into your app, see iCloud Design Guide.

Notification Center

Notification Center provides a way for users to receive and view app notifications in an attractive, unobtrusive way. For each app, users can specify how they want to be notified of an item’s arrival; they can also reveal Notification Center to view all the items that have been delivered.

When you use the NSUserNotification and NSUserNotificationCenter APIs introduced in OS X v10.8, you can configure the user-visible portions of a notification item, schedule items for delivery, and find out when items have been delivered. You can also determine whether your app has launched as a result of a notification and, if it has, whether that notification originated locally or remotely.

To learn more about integrating the Notification Center into your app, see NSUserNotification Class Reference and NSUserNotificationCenter Class Reference.

Sharing Service

The sharing service introduced in OS X v10.8 provides a consistent user experience for sharing content among many types of services. For example, a user might want to share a photo by attaching it to an email or a Twitter message, or sending it to another Mac user via AirDrop.

The new AppKit NSSharingService API allows you to get information about available services and share items with them directly. As a result, you can display a custom UI to present the services. You can also use the NSSharingServicePicker API to display a list of sharing services (including custom services that you define) from which the user can choose. When a service is performed, the system-provided sharing window is displayed. There the user can comment or add recipients. To learn more about the sharing service APIs, see NSSharingService Class Reference and NSSharingServicePicker Class Reference.

To allow your custom mail app to participate in sharing services, add the MailSharingSupported key to your Info.plist file and register a custom event handler, specifying the mail event class and the shim event ID. Then, in your event handler implementation, use the shud keyword to retrieve the event's descriptor data.


In OS X v10.8 users can turn on Gatekeeper, which allows them to block the installation of software that does not come from the Mac App Store and identified developers. If your app is not signed with a Developer ID certificate issued by Apple, it will not launch on systems that have this security option selected. If you plan to distribute your app outside of the Mac App Store, be sure to test the installation of your app on a Gatekeeper-enabled system so that you can provide a good user experience.

Xcode supports most of the tasks that you need to perform to get a Developer ID certificate and code sign your app. To learn how to submit your app to the Mac App Store—or test app installation on a Gatekeeper-enabled system—read Tools Workflow Guide for Mac.

Objective-C Enhancements

OS X v10.8 includes the following enhancements to Objective-C:

  • Default synthesis of accessor methods for declared properties

  • Object literals for NSArray, NSDictionary, and NSNumber

  • No need for forward declarations for methods that are used only within @implementation blocks

  • Streamlined object subscripting

  • Type-safe enums

64-Bit Compatibility

OS X v10.8 requires a Mac that uses the 64-bit kernel. Additionally, OS X v10.8 does not support 32-bit kernel extensions (KEXTs). Both 32-bit and 64-bit apps can run in OS X v10.8.

Framework-Level Features

The following sections highlight changes to frameworks and technologies in OS X v10.8.

New Frameworks

The following frameworks have been added in OS X v10.8:

  • Accounts (Accounts.framework). This framework provides a single sign-on model for supported account types. Single sign-on improves the user experience because apps no longer need to prompt a user separately for login information related to an account. It also simplifies the development model for you by managing the account authorization process for your app. To learn more about the Accounts API, see ACAccount Class Reference.

  • Audio Video Bridging (AudioVideoBridging.framework). This framework supports Audio Video Bridging (AVB) and implements the IEEE P1722.1 draft standard. AVB enhances the quality of service and provides guaranteed latency and bandwidth for media streams over an AVB network. The Audio Video Bridging API gives you access to the Entity discovery and control protocols of IEEE P1722.1 over an Ethernet network.

  • Event Kit (EventKit.framework). The Event Kit framework provides an interface for accessing a user’s calendar events and reminder items. You can use the APIs in this framework to get existing events and to add new events to the user’s calendar. Events that are created using Event Kit APIs are automatically propagated to the CalDAV or Exchange calendars on other devices, which allows your app to display up-to-date calendar information without requiring users to open the Calendar app. (Calendar events can include configurable alarms with rules for when they should be delivered.)

    You can also use Event Kit APIs to access reminder lists, create new reminders, add an alarm to a reminder, set the due and start date for a reminder, and mark a reminder as complete. To learn more about the Event Kit APIs, see Event Kit Framework Reference.

  • Game Kit (GameKit.framework). As described in Game Center, the Game Kit framework provides APIs that allow your app to participate in Game Center. You can use Game Kit APIs to display leaderboards in your game and to give users the opportunity to share their in-game achievements and play multiplayer games. To learn more about using Game Kit APIs in your app, see Game Kit Framework Reference.

  • GLKit (GLKit.framework). The GLKit framework provides libraries of commonly needed functions and classes that can help reduce the effort required to create an OpenGL app. In addition, the GLKit framework includes APIs that perform several optimized mathematical operations, reduce the effort in loading texture data, and provide standard implementations of commonly needed shader effects. To learn more about using GLKit APIs in your app, see GLKit Framework Reference.

  • Scene Kit (SceneKit.framework). The Scene Kit framework provides a high-level, Objective-C API that you can use to efficiently load, manipulate, and render 3D scenes in your app. Scene Kit allows you to import Digital Asset Exchange files (.dae files) that are created by popular content-creation applications and gives you access to the objects, lights, cameras, and geometry data that define a 3D scene. Using an approach based on scene graphs, Scene Kit makes it simple to modify, animate, and render your 3D scenes. For more information about using Scene Kit APIs in your app, see SceneKit Programming Guide.

  • Social (Social.framework). The Social framework provides an API for sending requests to supported social networking services that can perform operations on behalf of your users. You can also use the Social framework to retrieve information for integrating a user’s social networking accounts into your app. To learn more about using the Social framework in your app, see Social Framework Reference.

  • Video Toolbox (VideoToolbox.framework). The Video Toolbox framework comprises the 64-bit replacement for the QuickTime Image Compression Manager. The Video Toolbox APIs provide services for video compression and decompression, and for conversion between raster image formats stored in Core Video pixel buffers.


The following sections highlight changes and enhancements in the AppKit framework. For detailed information about changes in the AppKit programming interfaces, see AppKit Release Notes for macOS 10.13.

Layer-Backed Views

The AppKit framework introduces new NSView APIs that enhance the implementation and performance of layer-backed views. When you use layer-backed views in your app, Core Animation can perform view animations asynchronously, which can result in better, smoother animations. To benefit from the enhancements to layer-backed views in OS X v10.8, set the layerContentsRedrawPolicy property on your custom views to NSViewLayerContentsRedrawOnSetNeedsDisplay. If you do any custom drawing, refactor it to use subviews as much as possible (you can add subviews to a view at design time, or you can allow subviews to be added lazily in the layout method).

In addition, you can use other new NSView APIs to update a view’s layer declaratively. For example, you can return YES in wantsUpdateLayer and then implement updateLayer to set the layer’s properties. Typically, you set the layer’s contents to an NSImage object and set the contentsCenter property to specify the proper way to stretch the image. Or you can set simple layer properties, such as backgroundColor and borderColor. To learn more about the new NSView APIs, see NSView Class Reference.

Because a layer object often works with CGColorRef objects, you might need to convert between an NSColor object and a CGColorRef object frequently. To help you easily perform these conversions, the NSColor class provides the new CGColor and colorWithCGColor: methods. To learn more about new NSColor methods, see NSColor Class Reference.

In OS X v10.8, text rendering in transparent layers is enhanced. For example, NSTextField—in addition to other AppKit UI controls—can properly render text with font smoothing on a transparent layer background. At the same time, AppKit explicitly disables font smoothing in custom-rendered transparent layers to avoid drawing artifacts.


New AppKit APIs make it easier for you to adopt modern gestures in your app and to provide a better zoom experience without redrawing your content. For example, NSScrollView now has built-in support for the smart zoom gesture (that is, a two-finger double-tap on a trackpad). When you provide the semantic layout of your content, NSScrollView can intelligently magnify the content under the pointer. In addition, you can use this new API to respond to the lookup gesture (that is, a three-finger tap on a trackpad). To learn more about the new NSScrollView APIs, see NSScrollView Class Reference.

Page-Based UI

The new NSPageController class, which controls swipe navigation between views or view content, helps you implement a multipage book or browsing history user experience in your app. You can use NSPageController and its delegate to manage navigation through a predefined set of content views (such as the pages in a book) or a history of content snapshots, which changes when the user visits different views. To learn how to use NSPageController, see NSPageController Class Reference.

Text Alternatives

The new NSTextAlternatives class stores a list of alternatives for a specific piece of text and can notify your app when the user chooses an alternative. To support dictation, for example, you might use NSTextAlternatives to present a list of alternative interpretations for a word or phrase the user speaks. If the user chooses to replace the initial interpretation with an alternative, NSTextAlternatives notifies you of the choice so that you can update the text appropriately.

Auto Layout

Enhancements to various AppKit classes improve their support for Auto Layout. For example, you can use the new NSSplitView holding priority API to specify how the panes of a split view should react to changes in the split view's size. To allow the height of a fixed-width text field to grow when its content increases, you can use the new NSTextField method setPreferredMaxLayoutWidth. If you use NSMatrix objects in your app, you can use the new setAutorecalculatesCellSize method to cause the object’s cell contents to determine the cell size.

Block-Based Drawing for Offscreen Images

The new NSImage method imageWithSize:flipped:drawingHandler: allows you to create an image that delegates its drawing to a block. Because the block is invoked at draw time, the drawing can be adjusted to suit the destination’s pixel density, color space, and other properties. The imageWithSize:flipped:drawingHandler: method can be a good alternative to using the lockFocus and unlockFocus methods, especially when you need to support moving images between displays that have different properties. To learn how to optimize your app so that it looks great on a Retina display, see High Resolution Guidelines for OS X.

Auto Save

In OS X v10.8 some parts of the Auto Save user experience changed. If your document-based app participates in iCloud, the system automatically saves untitled documents in iCloud as soon as the user begins editing. (If your app doesn’t participate in iCloud, untitled documents are saved in the user’s Documents folder.) If the user provides a title in the Save dialog, the new title is used instead. To duplicate a document, the Duplicate menu item now allows users to supply a name for the document copy. When users close a duplicated document that has not been saved explicitly, they’re asked whether they want to keep the document or delete it.

When a user edits an old document, the default setting that governs whether an alert appears has changed from on to off. Specifically, the alert that states “The document is locked because you haven’t made any changes to it recently” does not appear unless the user turns on the setting in Time Machine preferences. By default, a document is considered old if it has not been changed in at least 2 weeks.

If a document-based app that adopts Auto Save is in the foreground when the user starts Time Machine, the Versions feature displays previous versions of the document.

AV Foundation

The AV Foundation framework includes the following enhancements:

  • The AVAsset and AVPlayerItem classes include new properties that help you find media-resource options that accommodate language preferences, accessibility requirements, and other needs, and then select them for playback.

  • New methods extend the AVPlayer class so that you can schedule playback to start at an arbitrary host time and can ensure that it remains synchronized with another time-based operation, such as audio playback that’s performed using Audio Toolbox APIs.

  • The new AVSampleBufferDisplayLayer class allows you to display a sequence of video frames in a Core Animation layer. You can also use this class to control timing and optional synchronization with an audio device clock.

  • The new AVPlayerItemOutput class, in conjunction with new AVPlayerItem methods, allows you to get decoded video frames during playback so that your app can process them.

Core Animation

Core Animation introduces the new drawsAsynchronously property for a CALayer object. When the value of this property is YES, the graphics context object that is passed to the layer’s drawInContext method can queue its drawing commands so that they are executed asynchronously. When drawing commands are executed asynchronously, drawing operations can be done more efficiently.

When you use the drawsAsynchronously property, make sure to handle the memory management of your app’s context resources (such as shadings, images, and functions) in accordance with the requirements of the Quartz 2D API. In particular, a resource must avoid referencing transient memory (such as data on the stack) because the resource might persist after the function returns to its caller.

Core Graphics

The Core Graphics framework introduces streaming APIs for capturing updates to the display in a real-time manner and for providing scaling and color-space-conversion services. The framework also adds support for viewing and modifying metadata for popular image formats.

Core Location

The Core Location framework introduces the CLGeocoder and CLPlacemark classes to give users information about a location. For example, you can use a geocoder object to convert latitude and longitude (that pinpoint a location) to a user-friendly description of that location. The user-friendly description—which typically includes street, city, and country information—is stored in a CLPlacemark object. You can also use a CLGeocoder object to convert an address dictionary from Contacts or a human-readable address string—such as “1 Infinite Loop, Cupertino, CA 95014”—into geographical coordinates.

The Core Location framework also enables region monitoring. In particular, you can use the startUpdatingForRegion and stopUpdatingForRegion methods to receive callbacks when the user enters or exits a region that you specify. To learn more about the new classes in the Core Location framework, see Core Location Framework Reference.

Core Media

The Core Media framework introduces the CMSync API, which defines two fundamental media time services objects:

  • CMClock, which represents a source of timing information such as mach_absolute_time or an audio device

  • CMTimebase, which represents a timeline that is under app control (that is, a timeline on which you can set the time and the rate at which the media plays)

The Core Media framework also introduces the CMAudioDeviceClock and CMMemoryPool APIs. The CMAudioDeviceClock API provides a CMClock object that’s synchronized to an audio device. The CMMemoryPool API maintains a pool of recently deallocated memory blocks so that subsequent allocations of the same size can be made more quickly. For example, clients of the Video Toolbox video compression services can get an allocator from a CMMemoryPool object and pass it to a VTCompressionSession object. As a result, the video encoder can benefit from pooling behavior when the encoder allocates memory for compressed video frames.

Core Text

The Core Text framework includes support for optical glyph bounds and unregistered data fonts. It also introduces:

  • AAT (Apple Advanced Typography) text features that help you access common OpenType layout tags

  • String attributes that allow you to use baseline alignments

  • The CTLineGetBoundsWithOptions function, which gives you finer-grained control of line metrics

To learn more about using Core Text in your app, see Core Text Programming Guide.


The Foundation framework introduces the following enhancements:

  • The new NSUUID class helps you create objects that represent various types of UUIDs (Universally Unique Identifiers). For example, you can create an NSUUID object with RFC 4122 v4 random bytes, or you can base the UUID on an existing string. To learn more about the NSUUID class, see NSUUID Class Reference.

  • The new NSXPCConnection class provides a Cocoa interface to the XPC library for communicating between processes, and allows you to use your own objects and classes. To learn more about the NSXPCConnection class, see NSXPCConnection Class Reference.

  • New NSFileManager API allows you to discover the currently active iCloud account and detect when the user logs into or out of it.

For detailed information about changes in the Foundation programming interfaces, see Foundation Release Notes for macOS 10.13 and iOS 11.


In OS X v10.8 three functions related to OpenGL context copying are deprecated:

Store Kit

The Store Kit framework introduces the ability to make your In-App Purchase content available in the Mac App Store. The content can be uploaded to iTunes Connect via Xcode or Application Loader and downloaded in your app using the following Store Kit APIs:

  • The SKPaymentQueue class has new methods to start, pause, and cancel downloads.

  • The new SKDownload class represents the status of a download from the Mac App Store and provides methods that allow you to get information about the download, including the percentage complete and an estimate of the time remaining.

System Configuration

The System Configuration framework introduces the captive network API, which allows apps to provide a better user experience when interacting with a captive network. (A captive network, such as a public Wi-Fi hotspot, requires user interaction before providing Internet access.) Captive network support (CNS) improves the user’s connectivity experience by identifying whether a network is captive and, if it is, looking for another app that might be able to handle the connection. If no such app can be found, CNS then attempts to log in with credentials the user has saved. If neither of these solutions works, CNS displays the network’s login webpage so that the user can log in to the network. Without CNS, users might not get prompted to log in to a captive network, and so they might assume that the resulting delay is the app’s fault.

You can use the captive network API to tell CNS to mark an interface as online or offline. You can also use it to provide information about the SSIDs (service set IDs) that CNS should relinquish control of in favor of apps that can handle captive network connectivity.

Carbon Core API Deprecations

In OS X v10.8, most of the APIs in the Carbon Core framework are deprecated (Carbon Core is a subframework of the Core Services umbrella framework). In many cases, there are alternative APIs you can use, such as APIs in the Core Foundation, Foundation, and Disk Arbitration frameworks.

Some of the deprecated APIs are high-level wrappers around functions in the POSIX or BSD layers, such as malloc, pthread, and sysctl. In place of using a deprecated wrapper function, you should use the appropriate lower-level API directly. In some cases, you can use GCD (Grand Central Dispatch) instead. Finally, some of the deprecated APIs are no longer needed or recommended, such as the bit-operation functions in ToolUtils.h. (The bit-operation functions were needed in Pascal development, and C provides bit operators.) To learn more about the Carbon Core APIs that are deprecated, see Carbon Core Deprecations.

App Features

Notable in OS X v10.8 are changes to Safari.


Safari 6.0 includes the following new features and enhancements:

  • SVG filters. SVG (scalable vector graphics) filters combine filter-primitive elements and light source elements into a single sophisticated filter, which you can then apply to any SVG element.

  • Web notifications. The web notifications API sends a notification from a Safari extension or webpage. Users receive these notifications in Notification Center, along with other notifications they choose to receive.

  • Redesigned Web Inspector. The Web Inspector in Safari 6.0 features a navigation sidebar—for displaying information about resources, storage, and instruments—and a details sidebar—for quickly and easily editing the CSS for any DOM element. The new Web Inspector also includes a more contextual JavaScript evaluation area that is separate from the error log, streamlined instrumentation and profiling tools, and a more accessible page source view.

  • The Web Audio API. JavaScript Web Audio API synthesizes and processes audio in web apps having complex audio requirements, such as a modern game audio engine or an interactive audio production app.

  • HTML5 media controllers. Using an HTML5 media controller, you can coordinate the playback of multiple HTML5 media elements. For example, you can use a media controller to synchronize a sign-language-interpretation track with a video track.

  • HTML5-timed text tracks. You can use an HTML5-timed text track to specify the timing at which text (such as captions or subtitles) appears within an HTML5 video element.

  • CSS filters. You can use CSS filters to apply pixel effects, such as invert and blur, to an image or webpage element. You can also combine CSS filters, and you can use CSS transitions and animations to animate changes to a filter.

To learn more about Safari 6.0, read Safari and WebKit Release Notes (login required).

Xcode Tools Enhancements

Xcode 4.4 adds numerous features that support OS X v10.8, notably:

For more information about Xcode enhancements, see What's New in Xcode.

BSD and Kernel Features

Grand Central Dispatch (GCD) and XPC (interprocess communication) objects support Automated Reference Counting (ARC) in Objective-C. Using GCD and XPC with ARC requires a minimum deployment target of OS X v10.8 (this functionality is unavailable if you have a 32-bit Intel machine).