Features

Interface

The iOS user interface is based upon direct manipulation, using multi-touch gestures such as swipe, tap, pinch, and reverse pinch. Interface control elements include sliders, switches, and buttons. Internal accelerometers are used by some applications to respond to shaking the device (one common result is the undo command) or rotating it in three dimensions (one common result is switching between portrait and landscape mode). Various accessibility functions enable users with vision and hearing disabilities to properly use iOS.

iOS devices boot to the homescreen, the primary navigation and information "hub" on iOS devices, analogous to the desktop found on personal computers. iOS homescreens are typically made up of app icons and widgets; app icons launch the associated app, whereas widgets display live, auto-updating content, such as a weather forecast, the user's email inbox, or a news ticker directly on the homescreen.

Along the top of the screen is a status bar, showing information about the device and its connectivity. The status bar itself contains two elements, the Control Center and the Notification Center. The Control Center can be "pulled" down from the top right of the notch, on the new iPhones, giving access to various toggles to manage the device more quickly without having to open the Settings. It is possible to manage brightness, volume, wireless connections, music player, etc.

Instead, scrolling from the top left to the bottom will open the Notification Center, which in the latest versions of iOS is very similar to the lockscreen. It displays notifications in chronological order and groups them by application. From the notifications of some apps it is possible to interact directly, for example by replying a message directly from it. Notifications are sent in two modes, the important notifications that are displayed on the lock screen and signaled by a distinctive sound, accompanied by a warning banner and the app badge icon, and the secondary mode where they are displayed in the Notification Center, but they are not shown on the lock screen, nor are they indicated by warning banners, badge icons or sounds.

It is possible to choose if notifications from an app can be shown on the lock screen, Notification Center, banner, or all three; whether the banner should be temporary or permanent; activate or deactivate the sound; choose whether to group by app or not and whether to show previews when locked. It is possible to turn off unwanted app notifications. Older notifications are automatically deleted after a few days.

A homescreen may be made up of several pages, between which the user can swipe back and forth, one of the ways to do this is to hold down on the "dots" shown on each page and swipe left or right.

To the right of the last page, the App Library lists and categorizes apps installed on the device. Apps within each category are arranged based on the frequency of their usage. In addition to a category for suggested apps, a "recent" category lists apps recently installed alongside App Clips recently accessed. Users can search for the app they want or browse them in alphabetical order.

iOS also integrates seamlessly with other programming frameworks and technologies, such as Apple Pay, HealthKit, and ResearchKit.

On iOS, the main page button is usually located at the top right. To go back in an application there is almost always a "back" button.

You can go back in 4 different ways, it varies depending on the context.

1. Press the "Back" button at the top left of the display
2. Swipe right from the left edge of the screen (gesture)
3. Press the "Finish" action at the top right of the screen
4. Scroll down on the screen content

The page title is practically always present and very visible, but it shrinks as the user scrolls down.

Navigation destinations that cannot be contained in the bottom tab bar can: be moved to a generic "More" tab or appear as actions in the top left or top right of other destinations.

Modal views are single-screen activities that are displayed by swiping into the foreground, while allowing the previous screen to peek up, retreating into the background. You can ignore them by scrolling down or tapping "Back" at the top.

Full screen views are media content such as photos or videos that take up the entire screen. They disappear on scrolling down.

Occasionally on iOS, important page actions appear on a lower toolbar.

Action menus can be activated by any button or by attempting to perform any action. They scroll from bottom to top.

A new feature in iOS 13 called "context menus" shows related actions when you touch and hold an item. When the context menu is displayed, the background is blurred.

To choose from a few options, a selection control is used. Selectors can appear anchored at the bottom or in line with the content (called date selectors). Date selectors take on the appearance of any other selection control, but with a column for day, month, and optionally year.

Alerts appear in the center of the screen, but there are also alerts that scroll up from the bottom of the screen (called "action panels"). Destructive actions (such as eliminating any element) are colored red.

The official font of iOS is San Francisco. It is designed for small text readability, and is used throughout the operating system, including third-party apps.

The icons are 180x180px in size for iPhones with a larger screen, usually models over 6 inches, including iPhone 11 Pro and iPhone 8 Plus, while it's 120x120px on iPhones with smaller displays.

Apple's official design language is called Human Interface.

Applications

iOS devices come with preinstalled Apple apps including Email, Apple Maps, TV, FaceTime, Podcast, Wallet, Health, and many more.

Applications ("apps") are the most general form of application software that can be installed on iOS. They are downloaded from the official catalog of the App Store digital store, where apps are subjected to security checks before being made available to users. In June 2017, Apple updated its guidelines to specify that app developers will no longer have the ability to use custom prompts for encouraging users to leave reviews for their apps. IOS applications can also be installed directly from an IPA file provided by the software distributor, via unofficial ways. They are written using iOS Software Development Kit (SDK) and, often, combined with Xcode, using officially supported programming languages, including Swift and Objective-C. Other companies have also created tools that allow for the development of native iOS apps using their respective programming languages.

Applications for iOS are mostly built using components of UIKit, a programming framework. It allows applications to have a consistent look and feel with the OS, nevertheless offering customization.

Elements automatically update along with iOS updates, automatically including new interface rules. UIKit elements are very adaptable, this allows developers to design a single app that looks the same on any iOS device. In addition to defining the iOS interface, UIKit defines the functionality of the application.

At first, Apple did not intend to release an SDK to developers, because they did not want third-party apps to be developed for iOS, building web apps instead. However, this technology never entered into common use, this led Apple to change its opinion, so in October 2007 the SDK for developers was announced, finally released on March 6, 2008.

The SDK includes an inclusive set of development tools, including an audio mixer and an iPhone simulator. It is a free download for Mac users. It is not available for Microsoft Windows PCs. To test the application, get technical support, and distribute applications through App Store, developers are required to subscribe to the Apple Developer Program.

Over the years, the Apple Store apps surpassed multiple major milestones, including 50,000, 100,000, 250,000, 500,000, 1 million, and 2 million apps. The billionth application was installed on April 24, 2009.

Home screen

The home screen, rendered by SpringBoard, displays application icons and a dock at the bottom where users can pin their most frequently used apps. The home screen appears whenever the user unlocks the device or presses the physical "Home" button while in another app. Before iOS 4 on the iPhone 3GS (or later), the screen's background could be customized only through jailbreaking, but can now be changed out-of-the-box. The screen has a status bar across the top to display data, such as time, battery level, and signal strength. The rest of the screen is devoted to the current application. When a passcode is set and a user switches on the device, the passcode must be entered at the Lock Screen before access to the Home screen is granted.

In iPhone OS 3, Spotlight was introduced, allowing users to search media, apps, emails, contacts, messages, reminders, calendar events, and similar content. In iOS 7 and later, Spotlight is accessed by pulling down anywhere on the home screen (except for the top and bottom edges that open Notification Center and Control Center). In iOS 9, there are two ways to access Spotlight. As with iOS 7 and 8, pulling down on any homescreen will show Spotlight. However, it can also be accessed as it was in iOS 3 – 6. This endows Spotlight with Siri suggestions, which include app suggestions, contact suggestions and news. In iOS 10, Spotlight is at the top of the now-dedicated "Today" panel.

Since iOS 3.2, users are able to set a background image for the Home Screen. This feature is only available on third-generation devices—iPhone 3GS, third-generation iPod touch (iOS 4.0 or newer), and all iPad models (since iOS 3.2)—or newer.

iOS 7 introduced a parallax effect on the Home Screen, which shifts the device's wallpaper and icons in response to the movement of the device, creating a 3D effect and an illusion of floating icons. This effect is also visible in the tab view of Mail and Safari.

Researchers found that users organize icons on their homescreens based on usage frequency and relatedness of the applications, as well as for reasons of usability and aesthetics.

System font

iOS originally used Helvetica as the system font. Apple switched to Helvetica Neue exclusively for the iPhone 4 and its Retina Display, and retained Helvetica as the system font for older iPhone devices on iOS 4. With iOS 7, Apple announced that they would change the system font to Helvetica Neue Light, a decision that sparked criticism for inappropriate usage of a light, thin typeface for low-resolution mobile screens. Apple eventually chose Helvetica Neue instead. The release of iOS 7 also introduced the ability to scale text or apply other forms of text accessibility changes through Settings. With iOS 9, Apple changed the font to San Francisco, an Apple-designed font aimed at maximum legibility and font consistency across its product lineup.

Folders

iOS 4 introduced folders, which can be created by dragging an application on top of another, and from then on, more items can be added to the folder using the same procedure. A title for the folder is automatically selected by the category of applications inside, but the name can also be edited by the user. When apps inside folders receive notification badges, the individual numbers of notifications are added up and the total number is displayed as a notification badge on the folder itself. Originally, folders on an iPhone could include up to 12 apps, while folders on iPad could include 20. With increasing display sizes on newer iPhone hardware, iOS 7 updated the folders with pages similar to the home screen layout, allowing for a significant expansion of folder functionality. Each page of a folder can contain up to nine apps, and there can be 15 pages in total, allowing for a total of 135 apps in a single folder. In iOS 9, Apple updated folder sizes for iPad hardware, allowing for 16 apps per page, still at 15 pages maximum, increasing the total to 240 apps.

Notification Center

Before iOS 5, notifications were delivered in a modal window and couldn't be viewed after being dismissed. In iOS 5, Apple introduced Notification Center, which allows users to view a history of notifications. The user can tap a notification to open its corresponding app, or clear it. Notifications are now delivered in banners that appear briefly at the top of the screen. If a user taps a received notification, the application that sent the notification will be opened. Users can also choose to view notifications in modal alert windows by adjusting the application's notification settings. Introduced with iOS 8, widgets are now accessible through the Notification Center, defined by 3rd parties.

When an app sends a notification while closed, a red badge appears on its icon. This badge tells the user, at a glance, how many notifications that app has sent. Opening the app clears the badge.

Accessibility

iOS offers various accessibility features to help users with vision and hearing disabilities. One major feature, VoiceOver, provides a voice reading information on the screen, including contextual buttons, icons, links and other user interface elements, and allows the user to navigate the operating system through gestures. Any apps with default controls and developed with a UIKit framework gets VoiceOver functionality built in. One example includes holding up the iPhone to take a photo, with VoiceOver describing the photo scenery. As part of a "Made for iPhone" program, introduced with the release of iOS 7 in 2013, Apple has developed technology to use Bluetooth and a special technology protocol to let compatible third-party equipment connect with iPhones and iPads for streaming audio directly to a user's ears. Additional customization available for Made for iPhone products include battery tracking and adjustable sound settings for different environments. Apple made further efforts for accessibility for the release of iOS 10 in 2016, adding a new pronunciation editor to VoiceOver, adding a Magnifier setting to enlarge objects through the device's camera, software TTY support for deaf people to make phone calls from the iPhone, and giving tutorials and guidelines for third-party developers to incorporate proper accessibility functions into their apps.

In 2012, Liat Kornowski from The Atlantic wrote that "the iPhone has turned out to be one of the most revolutionary developments since the invention of Braille", and in 2016, Steven Aquino of TechCrunch described Apple as "leading the way in assistive technology", with Sarah Herrlinger, Senior Manager for Global Accessibility Policy and Initiatives at Apple, stating that "We see accessibility as a basic human right. Building into the core of our products supports a vision of an inclusive world where opportunity and access to information are barrier-free, empowering individuals with disabilities to achieve their goals".

Multitasking

Multitasking for iOS was first released in June 2010 along with the release of iOS 4. Only certain devices—iPhone 4, iPhone 3GS, and iPod Touch 3rd generation—were able to multitask. The iPad did not get multitasking until iOS 4.2.1 in that November.

The implementation of multitasking in iOS has been criticized for its approach, which limits the work that applications in the background can perform to a limited function set and requires application developers to add explicit support for it.

Before iOS 4, multitasking was limited to a selection of the applications Apple included on the device. Users could however "jailbreak" their device in order to unofficially multitask. Starting with iOS 4, on third-generation and newer iOS devices, multitasking is supported through seven background APIs:

1. Background audio – application continues to run in the background as long as it is playing audio or video content
2. Voice over IP – application is suspended when a phone call is not in progress
3. Background location – application is notified of location changes
4. Push notifications
5. Local notifications – application schedules local notifications to be delivered at a predetermined time
6. Task completion – application asks the system for extra time to complete a given task
7. Fast app switching – application does not execute any code and may be removed from memory at any time

In iOS 5, three new background APIs were introduced:

1. Newsstand – application can download content in the background to be ready for the user
2. External Accessory – application communicates with an external accessory and shares data at regular intervals
3. Bluetooth Accessory – application communicates with a bluetooth accessory and shares data at regular intervals

In iOS 7, Apple introduced a new multitasking feature, providing all apps with the ability to perform background updates. This feature prefers to update the user's most frequently used apps and prefers to use Wi-Fi networks over a cellular network, without markedly reducing the device's battery life.

Switching applications

In iOS 4.0 to iOS 6.x, double-clicking the home button activates the application switcher. A scrollable dock-style interface appears from the bottom, moving the contents of the screen up. Choosing an icon switches to an application. To the far left are icons which function as music controls, a rotation lock, and on iOS 4.2 and above, a volume controller.

With the introduction of iOS 7, double-clicking the home button also activates the application switcher. However, unlike previous versions it displays screenshots of open applications on top of the icon and horizontal scrolling allows for browsing through previous apps, and it is possible to close applications by dragging them up, similar to how WebOS handled multiple cards.

With the introduction of iOS 9, the application switcher received a significant visual change; while still retaining the card metaphor introduced in iOS 7, the application icon is smaller, and appears above the screenshot (which is now larger, due to the removal of "Recent and Favorite Contacts"), and each application "card" overlaps the other, forming a rolodex effect as the user scrolls. Now, instead of the home screen appearing at the leftmost of the application switcher, it appears rightmost. In iOS 11, the application switcher receives a major redesign. In the iPad, the Control Center and app switcher are combined. The app switcher in the iPad can also be accessed by swiping up from the bottom. In the iPhone, the app switcher cannot be accessed if there are no apps in the RAM.

Ending tasks

In iOS 4.0 to iOS 6.x, briefly holding the icons in the application switcher makes them "jiggle" (similarly to the homescreen) and allows the user to force quit the applications by tapping the red minus circle that appears at the corner of the app's icon. Clearing applications from multitasking stayed the same from iOS 4.0 through 6.1.6, the last version of iOS 6.

As of iOS 7, the process has become faster and easier. In iOS 7, instead of holding the icons to close them, they are closed by simply swiping them upwards off the screen. Up to three apps can be cleared at a time compared to one in versions up to iOS 6.1.6.

Task completion

Task completion allows apps to continue a certain task after the app has been suspended. As of iOS 4.0, apps can request up to ten minutes to complete a task in the background. This doesn't extend to background up- and downloads though (e.g. if a user starts a download in one application, it won't finish if they switch away from the application).

Siri

Siri (/ˈsɪəri/) is an intelligent personal assistant integrated into iOS. The assistant uses voice queries and a natural language user interface to answer questions, make recommendations, and perform actions by delegating requests to a set of Internet services. The software adapts to users' individual language usages, searches, and preferences, with continuing use. Returned results are individualized.

Originally released as an app for iOS in February 2010, it was acquired by Apple two months later, and then integrated into iPhone 4S at its release in October 2011. At that time, the separate app was also removed from the iOS App Store.

Siri supports a wide range of user commands, including performing phone actions, checking basic information, scheduling events and reminders, handling device settings, searching the Internet, navigating areas, finding information on entertainment, and is able to engage with iOS-integrated apps. With the release of iOS 10 in 2016, Apple opened up limited third-party access to Siri, including third-party messaging apps, as well as payments, ride-sharing, and Internet calling apps. With the release of iOS 11, Apple updated Siri's voices for more clear, human voices, it now supports follow-up questions and language translation, and additional third-party actions.

Game Center

Game Center is an online multiplayer "social gaming network" released by Apple. It allows users to "invite friends to play a game, start a multiplayer game through matchmaking, track their achievements, and compare their high scores on a leaderboard." iOS 5 and above adds support for profile photos.

Game Center was announced during an iOS 4 preview event hosted by Apple on April 8, 2010. A preview was released to registered Apple developers in August. It was released on September 8, 2010 with iOS 4.1 on iPhone 4, iPhone 3GS, and iPod Touch 2nd generation through 4th generation. Game Center made its public debut on the iPad with iOS 4.2.1. There is no support for the iPhone 3G, original iPhone and the first-generation iPod Touch (the latter two devices did not have Game Center because they did not get iOS 4). However, Game Center is unofficially available on the iPhone 3G via a hack.