Welcome to Android 4.2, the latest version ofJelly Bean!
Android 4.2 has performance optimizations, a refreshed system UI, and great new features for users and developers. This document provides a glimpse of what's new for developers.
See the Android 4.2 APIs document for a detailed look at the new developer APIs.
Find out more about the new Jelly Bean features for users at www.android.com.
Faster, Smoother, More Responsive
Android 4.2 builds on the performance improvements already included in Jelly Bean —vsync timing, triple buffering, reduced touch latency, and CPU input boost — and adds new optimizations that make Android even faster.
Improvements in the hardware-accelerated 2D renderer make common animations such as scrolling and swiping smoother and faster. In particular, drawing is optimized for layers, clipping and certain shapes (rounded rects, circles and ovals).
A variety of WebView rendering optimizations make scrolling of web pages smoother and free from jitter and lags.
Android’s Renderscript Compute is the first computation platform ported to run directly on a mobile device GPU. It automatically takes advantage of GPU computation resources whenever possible, dramatically improving performance for graphics and image processing. Any app using Renderscript on a supported device can benefit immediately from this GPU integration without recompiling.
Refined, refreshed UI
Android 4.2 refines the Jelly Bean user experience and brings familiar Android UI patterns such as status bar, system bar, and notifications window to all tablets.
All screen sizes now feature the status bar on top, with pull-down access to notifications and a new Quick Settings menu. The familiar system bar appears on the bottom, with buttons easily accessible from either hand. The Application Tray is also available on all screen sizes.
One tablet, many users
Now several users can share a single Android tablet, with each user having convenient access to a dedicated user space. Users can switch to their spaces with a single touch from the lock screen.
On a multiuser device, Android gives each user a separate environment, including user-specific emulated SD card storage. Users also have their own homescreens, widgets, accounts, settings, files, and apps, and the system keeps these separate. All users share core system services, but the system ensures that each user's applications and data remain isolated. In effect, each of the multiple users has his or her own Android device.
Users can install and uninstall apps at any time in their own environments. To save storage space, Google Play downloads an APK only if it's not already installed by another user on the device. If the app is already installed, Google Play records the new user's installation in the usual way but doesn't download another copy of the app. Multiple users can run the same copy of an APK because the system creates a new instance for each user, including a user-specific data directory.
For developers, multi-user support is transparent — your apps do not need to do anything special to run normally in a multi-user environment and there are no changes you need to make in your existing or published APKs. The system manages your app in each user space just as it does in a single-user environment.
New ways to engage users
Lock screen widgets
In Android 4.2, users can place app widgets directly on their lock screens, for instant access to favorite app content without having to unlock. Users can add as many as five lock screen widgets, choosing from widgets provided by installed apps. The lock screen displays each widget in its own panel, letting users swipe left and right to view different panels and their widgets.
Like all app widgets, lock screen widgets can display any kind of contentand they can accept direct user interaction. They can be entirely self-contained, such as a widget that offers controls to play music, or they can let users jump straight to an Activity in your app, after unlocking along the way as needed.
For developers, lock screen widgets offer a great new way to engage users. They let you put your content in front of users in a location they’ll see often, and they give you more opportunities to bring users directly into your app.
You can take advantage of this new capability by building a new app widget or by extending an existing home screen widget. If your app already includes home screen widgets, you can extend them to the lock screen with minimal change. To give users an optimal experience, you can update the widget to use the full lock screen area when available and resize when needed on smaller screens. You can also add features to your widgets that might be especially useful or convenient on the lock screen.
Daydream is an interactive screensaver mode that starts when a user’s device is docked or charging. In this mode, the system launches a daydream — a remote content service provided by an installed app — as the device screensaver. A user can enable Daydream from the Settings app and then choose the daydream to display.
Daydreams combine the best capabilities of live wallpapers and home screen widgets, but they are more powerful. They let you offer the any kind of content in a completely new context, with user interactions such as flipping through photos, playing audio or video, or jumping straight into your app with a single touch.
Because daydreams can start automatically when a device is charging or docked, they also give your app a great way to support new types of user experiences, such as leanback or exhibition mode, demo or kiosk mode, and "attract mode" — all without requiring special hardware.
Daydreams are similar to Activities and can do anything that Activity can do — from rendering a UI hierarchy (without using RemoteViews) to drawing directly using Canvas, OpenGL, SurfaceTexture, and more. They can play video and audio and they can even accept direct user interaction. However, daydreams are not Activities, so they don’t affect the backstack or appear in Recents and they cannot be launched directly from your app.
Implementing a daydream is straightforward and you can take advantage of UI components and resources that you’ve already created for other parts of your app. You can provide multiple daydreams in your app and you can offer distinct content and display settings for each.
External display support
Android 4.2 introduces platform support for external displays that goes far beyond mirroring — apps can now target unique content to any one or multiple displays that are attached to an Android device. Apps can build on this to deliver new kinds of interaction and entertainment experiences to users.
Apps interact with displays through a new display manager system service. Your app can enumerate the displays and check the capabilities of each, including size, density, display name, ID, support for secure video, and more. Your app can also receive callbacks when displays are added or removed or when their capabilities change, to better manage your content on external displays.
To make it easy to show content on an external display, the framework provides a new UI object called a Presentation — a type of dialog that represents a window for your app’s content on a specific external display. Your app just gives the display to use, a theme for the window, and any unique content to show. The Presentation handles inflating resources and rendering your content according to the characteristics of the targeted display.
A Presentation gives your app full control over the remote display window and its content and lets you manage it based on user input events such as key presses, gestures, motion events, and more. You can use all of the normal tools to create a UI and render content in the Presentation, from building an arbitrary view hierarchy to using SurfaceView or SurfaceTexture to draw directly into the window for streamed content or camera previews.
Preferred display selection
When multiple external displays are available, you can create as many Presentations as you need, with each one showing unique content on a specific display. In many cases, you might only want to show your content on a single external display — but always on the that’s best for Presentation content. For this, the system can help your app choose the best display to use.
To find the best display to use, your app can query the display manager for the system’s preferred Presentation displayand receive callbacks when that display changes. Alternatively, you can use the media router service, extended in Android 4.2, to receive notifications when a system video route changes. Your app can display content by default in the main Activity until a preferred Presentation display is attached, at which time it can automatically switch to Presentation content on the preferred display. Your apps can also use media router’s MediaRouteActionProvider and MediaRouteButton to offer standard display-selection UI.
For apps that handle protected or encrypted content, the display API now reports the secure video capabilities of attached displays. Your app query a display to find out if it offers a secure video output or provides protected graphics buffers and then choose the appropriate content stream or decoding to make the content viewable. For additional security on SurfaceView objects, your app can set a secure flag to indicate that the contents should never appear in screenshots or on a non-secure display output, even when mirrored.
Starting in Android 4.2, users on supported devices can connect to an external display over Wi-Fi, using Miracast, a peer-to-peer wireless display standard created by the Wi-Fi Alliance. When a wireless display is connected, users can stream any type of content to the big screen, including photos, games, maps, and more.
Apps can take advantage of wireless displays in the same way as they do other external displays and no extra work is needed. The system manages the network connection and streams your Presentation or other app content to the wireless display as needed.
Native RTL support
Android 4.2 introduces full native support for RTL (right-to-left) layouts, including layout mirroring. With native RTL support, you can deliver the same great app experience to all of your users, whether their language uses a script that reads right-to-left or one that reads left-to-right.
When the user switches the system language to a right-to-left script, the system now provides automatic mirroring of app UI layouts and all view widgets, in addition to bidi mirroring of text elements for both reading and character input.
Your app can take advantage of RTL layout mirroring in your app with minimal effort. If you want the app to be mirrored, you simply declare a new attribute in your app manifest and change all "left/right" layout properties to new "start/end" equivalents. The system then handles the mirroring and display of your UI as appropriate.
For precise control over your app UI, Android 4.2 includes new APIs that let you manage layout direction, text direction, text alignment, gravity, and locale direction in View components. You can even create custom versions of layout, drawables, and other resources for display when a right-to-left script is in use.
To help you debug and optimize your custom right-to-left layouts, the HierarchyViewer tool now lets you see start/end properties, layout direction, text direction, and text alignment for all the Views in the hierarchy,
Enhancements for international languages
Android 4.2 includes a variety of font and character optimizations for international users:
- For Korean users, a new font choice is available — Nanum (나눔글꼴) Gothic, a unicode font designed especially for the Korean-language script.
- Improved support for Japanese vertical text displayed in WebViews.
- Improved font kerning and positioning for Indic, Thai, Arabic, and Hebrew default fonts.
The default Android keyboard also includes an updated set of dictionaries:
- Improved dictionaries for French (with bigram support), English, and Russian
- New dictionaries for Danish, Greek, Finnish, Lithuanian, Latvian, Polish, Slovenian, Serbian, Swedish, Turkish
New ways to create beautiful UI
For more control over your UI components and to make them more modular, Android 4.2 lets you nest Fragments inside of Fragments. For any Fragment, a new Fragment manager lets you insert other Fragments as child nodes in the View hierarchy.
You can use nested Fragments in a variety of ways, but they are especially useful for implementing dynamic and reusable UI components inside of a UI component that is itself dynamic and reusable. For example, if you use ViewPager to create fragments that swipe left and right, you can now insert fragments into each Fragment of the view pager.
To let you take advantage of nested Fragments more broadly in your app, this capability is added to the latest version of the Android Support Library.
The system now helps accessibility services distinguish between touch exploration and accessibility gestures while in touch-exploration mode. When a user touches the screen, the system notifies the service that a generic touch interaction has started. It then tracks the speed of the touch interaction and determines whether it is a touch exploration (slow) or accessibility gesture (fast) and notifies the service. When the touch interaction ends, the system notifies the service.
The system provides a new global accessibility option that lets an accessibility service open the Quick Settings menu based on an action by the user. Also added in Android 4.2 is a new accessibility feedback type for Braille devices.
To give accessibility services insight into the meaning of Views for accessibility purposes, the framework provides new APIs for associating a View as the label for another View. The label for each View is available to accessibility services through AccessibilityNodeInfo.
Improved Camera with HDR
Android 4.2 introduces a new camera hardware interface and pipeline for improved performance. On supported devices, apps can use a new HDR camera scene mode to capture an image using high dynamic range imaging techniques.
Additionally, the framework now provides an API to let apps check whether the camera shutter sound can be disabled. Apps can then let the user disable the sound or choose an alternative sound in place of the standard shutter sound, which is recommended.
In Android 4.2, Renderscript Compute introduces new scripting features, new optimizations, and direct GPU integration for the highest performance in computation operations.
Filterscript is a subset of Renderscript that is focused on optimized image processing across a broad range of device chipsets. Developers can write their image processing operations in Filterscript using the standard Renderscript runtime API, but within stricter constraints that ensure wider compatibility and improved optimization across CPUs, GPUs, and DSPs.
Filterscript is ideal for hardware-accelerating simple image-processing and computation operations such as those that might be written for OpenGL ES fragment shaders. Because it places a relaxed set of constraints on hardware, your operations are optimized and accelerated on more types of device chipsets. Any app targeting API level 17 or higher can make use of Filterscript.
In Android 4.2, Renderscript adds support for a set of script intrinsics — pre-implemented filtering primitives that are accelerated to reduce the amount of code that you need to write and to ensure that your app gets the maximum performance gain possible.
Intrinsics are available for blends, blur, color matrix, 3x3 and 5x5 convolve, per-channel lookup table, and converting an Android YUV buffer to RGB.
You can now create groups of Renderscript scripts and execute them all with a single call as though they were part of a single script. This allows Renderscript to optimize execution of the scripts in ways that it could not do if the scripts were executed individually.
Renderscript image-processing benchmarks run on different Android platform versions (Android 4.0, 4.1, and 4.2) in CPU only on a Galaxy Nexus device.
Renderscript image-processing benchmarks comparing operations run with GPU + CPU to those run in CPU only on the same Nexus 10 device.
If you have a directed acyclic graph of Renderscript operations to run, you can use a builder class to create a script group defining the operations. At execution time, Renderscript optimizes the run order and the connections between these operations for best performance.
Ongoing optimization improvements
When you use Renderscript for computation operations, you apps benefit from ongoing performance and optimization improvements in the Renderscript engine itself, without any impact on your app code or any need for recompilation.
As optimization improves, your operations execute faster and on more chipsets, without any work on your part. The chart at right highlights the performance gain delivered by ongoing Renderscript optimization improvements across successive versions of the Android platform.
Renderscript Compute is the first computation platform ported to run directly on a mobile device GPU. It now automatically takes advantage of GPU computation resources whenver possible to improve performance. With GPU integration, even the most complex computations for graphics or image processing can execute with dramatically improved performance.
Any app using Renderscript on a supported device can benefit immediately from this GPU integration, without recompiling. The Nexus 10 tablet is the first device to support this integration.
New built-in developer options
The Android 4.2 system includes a variety of new developer options that make it easier to create great looking apps that perform well. The new options expose features for debugging and profiling your app from any device or emulator.
New developer options in Android 4.2 include:
- Take bug report — immediately takes a screen shot and dumps device state information to local file storage, then attaches them to a new outgoing email message.
- Power menu bug reports — Adds a new option to the device power menu and quick settings to take a bug report (see above).
- Verify apps over usb — Allows you to disable app checks for sideloading apps over USB, while still checking apps from other sources like the browser. This can speed up the development process while keeping the security feature enabled.
- Show hardware layers updates — Flashes hardware layers green when they update.
- Show GPU overdraw — Highlights GPU overdraw areas.
- Force 4x MSAA — Enables 4x MSAA in Open GL ES 2.0 apps.
- Simulate secondary displays — Creates one or more non-secure overlay windows on the current screen for use as a simulated remote display. You can control the simulated display’s size and density.
- Enable OpenGL traces — Lets you trace OpenGL execution using Logcat, Systrace, or callstack on glGetError.
New Platform Technologies
Android 4.2 includes a variety of new and enhanced platform technologies to support innovative communications use-cases across a broad range of hardware devices. In most cases, the new platform technologies and enhancements do not directly affect your apps, so you can benefit from them without any modification.
Every Android release includes dozens of security enhancements to protect users. Here are some of the enhancements in Android 4.2:
- Application verification — Users can choose to enable “Verify Apps" and have applications screened by an application verifier, prior to installation. App verification can alert the user if they try to install an app that might be harmful; if an application is especially bad, it can block installation.
- More control of premium SMS — Android will provide a notification if an application attempts to send SMS to a short code that uses premium services which might cause additional charges. The user can choose whether to allow the application to send the message or block it.
- Always-on VPN — VPN can be configured so that applications will not have access to the network until a VPN connection is established. This prevents applications from sending data across other networks.
- Certificate Pinning — The libcore SSL implementation now supports certificate pinning. Pinned domains will receive a certificate validation failure if the certificate does not chain to a set of expected certificates. This protects against possible compromise of Certificate Authorities.
- Improved display of Android permissions — Permissions have been organized into groups that are more easily understood by users. During review of the permissions, the user can click on the permission to see more detailed information about the permission.
- installd hardening — The installd daemon does not run as the root user, reducing potential attack surface for root privilege escalation.
- init script hardening — init scripts now apply O_NOFOLLOW semantics to prevent symlink related attacks.
- FORTIFY_SOURCE — Android now implements FORTIFY_SOURCE. This is used by system libraries and applications to prevent memory corruption.
- ContentProvider default configuration — Applications which target API level 17 will have “export” set to “false” by default for each ContentProvider, reducing default attack surface for applications.
- Cryptography — Modified the default implementations of SecureRandom and Cipher.RSA to use OpenSSL. Added SSLSocket support for TLSv1.1 and TLSv1.2 using OpenSSL 1.0.1
- Security Fixes — Upgraded open source libraries with security fixes include WebKit, libpng, OpenSSL, and LibXML. Android 4.2 also includes fixes for Android-specific vulnerabilities. Information about these vulnerabilities has been provided to Open Handset Alliance members and fixes are available in Android Open Source Project. To improve security, some devices with earlier versions of Android may also include these fixes.
New Bluetooth stackAndroid 4.2 introduces a new Bluetooth stack optimized for use with Android devices. The new Bluetooth stack developed in collaboration between Google and Broadcom replaces the stack based on BlueZ and provides improved compatibility and reliability.
Android 4.2 improves support for low-latency audio playback, starting from the improvements made in Android 4.1 release for audio output latency using OpenSL ES, Soundpool and tone generator APIs. These improvements depend on hardware support — devices that offer these low-latency audio features can advertise their support to apps through a hardware feature constant. New AudioManager APIs are provided to query the native audio sample rate and buffer size, for use on devices which claim this feature.
New camera hardware interfaceAndroid 4.2 introduces a new implementation of the camera stack. The camera subsystem includes the implementations for components in the camera pipeline such as burst mode capture with processing controls.
New NFC hardware interface and controller interfaceAndroid 4.2 introduces support for controllers based on the NCI standard from the NFC-Forum. NCI provides a standard communication protocol between an NFC Controller (NFCC) and a device Host, and the new NFC stack developed in collaboration between Google and Broadcom supports it.
Dalvik runtime optimizations
The Dalvik runtime includes enhancements for performance and security across a wider range of architectures:
- x86 JIT support from Intel and MIPS JIT support from MIPS
- Optimized garbage-collection parameters for devices with > 512MB
- Default implementations of SecureRandom and Cipher.RSA now use OpenSSL
- SSLSocket support for TLSv1.1 and TLSv1.2 via OpenSSL 1.0.1
- New intrinsic support for StrictMath methods abs, min, max, and sqrt
- BouncyCastle updated to 1.47
- zlib updated to 1.27
- dlmalloc updated to 2.8.6