Android 4.2 Compatibility Definition

Revision 2
Last updated: Feb 17, 2013

Copyright © 2012, Google Inc. All rights reserved.
[email protected]

Table of Contents

1. Introduction

This document enumerates the requirements that must be met in order for devices to be compatible with Android 4.2.

The use of "must", "must not", "required", "shall", "shall not", "should", "should not", "recommended", "may" and "optional" is per the IETF standard defined in RFC2119 [Resources, 1].

As used in this document, a "device implementer" or "implementer" is a person or organization developing a hardware/software solution running Android 4.2. A "device implementation" or "implementation" is the hardware/software solution so developed.

To be considered compatible with Android 4.2, device implementations MUST meet the requirements presented in this Compatibility Definition, including any documents incorporated via reference.

Where this definition or the software tests described in Section 10 is silent, ambiguous, or incomplete, it is the responsibility of the device implementer to ensure compatibility with existing implementations.

For this reason, the Android Open Source Project [Resources, 3] is both the reference and preferred implementation of Android. Device implementers are strongly encouraged to base their implementations to the greatest extent possible on the "upstream" source code available from the Android Open Source Project. While some components can hypothetically be replaced with alternate implementations this practice is strongly discouraged, as passing the software tests will become substantially more difficult. It is the implementer's responsibility to ensure full behavioral compatibility with the standard Android implementation, including and beyond the Compatibility Test Suite. Finally, note that certain component substitutions and modifications are explicitly forbidden by this document.

2. Resources

1. IETF RFC2119 Requirement Levels: http://www.ietf.org/rfc/rfc2119.txt
2. Android Compatibility Program Overview: http://source.android.com/docs/compatibility/index.html
3. Android Open Source Project: http://source.android.com/
4. API definitions and documentation: http://developer.android.com/reference/packages.html
5. Android Permissions reference: http://developer.android.com/reference/android/Manifest.permission.html
6. android.os.Build reference: http://developer.android.com/reference/android/os/Build.html
7. Android 4.2 allowed version strings: http://source.android.com/docs/compatibility/4.2/versions.html
8. Renderscript: http://developer.android.com/guide/topics/graphics/renderscript.html
9. Hardware Acceleration: http://developer.android.com/guide/topics/graphics/hardware-accel.html
10. android.webkit.WebView class: http://developer.android.com/reference/android/webkit/WebView.html
11. HTML5: http://www.whatwg.org/specs/web-apps/current-work/multipage/
12. HTML5 offline capabilities: http://dev.w3.org/html5/spec/Overview.html#offline
13. HTML5 video tag: http://dev.w3.org/html5/spec/Overview.html#video
14. HTML5/W3C geolocation API: http://www.w3.org/TR/geolocation-API/
15. HTML5/W3C webdatabase API: http://www.w3.org/TR/webdatabase/
16. HTML5/W3C IndexedDB API: http://www.w3.org/TR/IndexedDB/
17. Dalvik Virtual Machine specification: available in the Android source code, at dalvik/docs
18. AppWidgets: http://developer.android.com/guide/practices/ui_guidelines/widget_design.html
19. Notifications: http://developer.android.com/guide/topics/ui/notifiers/notifications.html
20. Application Resources: http://code.google.com/android/reference/available-resources.html
21. Status Bar icon style guide: http://developer.android.com/guide/practices/ui_guidelines/icon_design_status_bar.html
22. Search Manager: http://developer.android.com/reference/android/app/SearchManager.html
23. Toasts: http://developer.android.com/reference/android/widget/Toast.html
24. Themes: http://developer.android.com/guide/topics/ui/themes.html
25. R.style class: http://developer.android.com/reference/android/R.style.html
26. Live Wallpapers: https://android-developers.googleblog.com/2010/02/live-wallpapers.html
27. Android Device Administration: http://developer.android.com/guide/topics/admin/device-admin.html
28. DevicePolicyManager reference: http://developer.android.com/reference/android/app/admin/DevicePolicyManager.html
29. Android Accessibility Service APIs: http://developer.android.com/reference/android/accessibilityservice/package-summary.html
30. Android Accessibility APIs: http://developer.android.com/reference/android/view/accessibility/package-summary.html
31. Eyes Free project: http://code.google.com/p/eyes-free
32. Text-To-Speech APIs: http://developer.android.com/reference/android/speech/tts/package-summary.html
33. Reference tool documentation (for adb, aapt, ddms, systrace): http://developer.android.com/guide/developing/tools/index.html
34. Android apk file description: http://developer.android.com/guide/topics/fundamentals.html
35. Manifest files: http://developer.android.com/guide/topics/manifest/manifest-intro.html
36. Monkey testing tool: https://developer.android.com/studio/test/other-testing-tools/monkey
37. Android android.content.pm.PackageManager class and Hardware Features List: http://developer.android.com/reference/android/content/pm/PackageManager.html
38. Supporting Multiple Screens: http://developer.android.com/guide/practices/screens_support.html
39. android.util.DisplayMetrics: http://developer.android.com/reference/android/util/DisplayMetrics.html
40. android.content.res.Configuration: http://developer.android.com/reference/android/content/res/Configuration.html
41. android.hardware.SensorEvent: http://developer.android.com/reference/android/hardware/SensorEvent.html
42. Bluetooth API: http://developer.android.com/reference/android/bluetooth/package-summary.html
43. NDEF Push Protocol: http://source.android.com/docs/compatibility/ndef-push-protocol.pdf
44. MIFARE MF1S503X: http://www.nxp.com/documents/data_sheet/MF1S503x.pdf
45. MIFARE MF1S703X: http://www.nxp.com/documents/data_sheet/MF1S703x.pdf
46. MIFARE MF0ICU1: http://www.nxp.com/documents/data_sheet/MF0ICU1.pdf
47. MIFARE MF0ICU2: http://www.nxp.com/documents/short_data_sheet/MF0ICU2_SDS.pdf
48. MIFARE AN130511: http://www.nxp.com/documents/application_note/AN130511.pdf
49. MIFARE AN130411: http://www.nxp.com/documents/application_note/AN130411.pdf
50. Camera orientation API: http://developer.android.com/reference/android/hardware/Camera.html#setDisplayOrientation(int)
51. Camera: http://developer.android.com/reference/android/hardware/Camera.html
52. Android Open Accessories: http://developer.android.com/guide/topics/usb/accessory.html
53. USB Host API: http://developer.android.com/guide/topics/usb/host.html
54. Android Security and Permissions reference: http://developer.android.com/guide/topics/security/security.html
55. Apps for Android: http://code.google.com/p/apps-for-android
56. Android DownloadManager: http://developer.android.com/reference/android/app/DownloadManager.html
57. Android File Transfer: http://www.android.com/filetransfer
58. Android Media Formats: http://developer.android.com/guide/appendix/media-formats.html
59. HTTP Live Streaming Draft Protocol: http://tools.ietf.org/html/draft-pantos-http-live-streaming-03
60. NFC Connection Handover: http://www.nfc-forum.org/specs/spec_list/#conn_handover
61. Bluetooth Secure Simple Pairing Using NFC: http://www.nfc-forum.org/resources/AppDocs/NFCForum_AD_BTSSP_1_0.pdf
62. Wifi Multicast API: http://developer.android.com/reference/android/net/wifi/WifiManager.MulticastLock.html
63. Action Assist: http://developer.android.com/reference/android/content/Intent.html#ACTION_ASSIST
64. USB Charging Specification: http://www.usb.org/developers/devclass_docs/USB_Battery_Charging_1.2.pdf
65. Android Beam: http://developer.android.com/guide/topics/nfc/nfc.html
66. Android USB Audio: http://developer.android.com/reference/android/hardware/usb/UsbConstants.html#USB_CLASS_AUDIO
67. Android NFC Sharing Settings: http://developer.android.com/reference/android/provider/Settings.html#ACTION_NFCSHARING_SETTINGS
68. Wifi Direct (Wifi P2P): http://developer.android.com/reference/android/net/wifi/p2p/WifiP2pManager.html
69. Lock and Home Screen Widget: http://developer.android.com/reference/android/appwidget/AppWidgetProviderInfo.html
70. UserManager reference: http://developer.android.com/reference/android/os/UserManager.html
71. External Storage reference: https://source.android.com/docs/core/storage
72. External Storage APIs: http://developer.android.com/reference/android/os/Environment.html
73. SMS Short Code: http://en.wikipedia.org/wiki/Short_code
74. Media Remote Control Client: http://developer.android.com/reference/android/media/RemoteControlClient.html
75. Display Manager: http://developer.android.com/reference/android/hardware/display/DisplayManager.html
76. Dreams: http://developer.android.com/reference/android/service/dreams/DreamService.html
77. Android Application Development-Related Settings: http://developer.android.com/reference/android/provider/Settings.html#ACTION_APPLICATION_DEVELOPMENT_SETTINGS

Camera: http://developer.android.com/reference/android/hardware/Camera.Parameters.html

Many of these resources are derived directly or indirectly from the Android 4.2 SDK, and will be functionally identical to the information in that SDK's documentation. In any cases where this Compatibility Definition or the Compatibility Test Suite disagrees with the SDK documentation, the SDK documentation is considered authoritative. Any technical details provided in the references included above are considered by inclusion to be part of this Compatibility Definition.

3. Software

3.1. Managed API Compatibility

The managed (Dalvik-based) execution environment is the primary vehicle for Android applications. The Android application programming interface (API) is the set of Android platform interfaces exposed to applications running in the managed VM environment. Device implementations MUST provide complete implementations, including all documented behaviors, of any documented API exposed by the Android 4.2 SDK [Resources, 4].

Device implementations MUST NOT omit any managed APIs, alter API interfaces or signatures, deviate from the documented behavior, or include no-ops, except where specifically allowed by this Compatibility Definition.

This Compatibility Definition permits some types of hardware for which Android includes APIs to be omitted by device implementations. In such cases, the APIs MUST still be present and behave in a reasonable way. See Section 7 for specific requirements for this scenario.

3.2. Soft API Compatibility

In addition to the managed APIs from Section 3.1, Android also includes a significant runtime-only "soft" API, in the form of such things such as Intents, permissions, and similar aspects of Android applications that cannot be enforced at application compile time.

3.2.1. Permissions

Device implementers MUST support and enforce all permission constants as documented by the Permission reference page [Resources, 5]. Note that Section 10 lists additional requirements related to the Android security model.

3.2.2. Build Parameters

The Android APIs include a number of constants on the android.os.Build class [Resources, 6] that are intended to describe the current device. To provide consistent, meaningful values across device implementations, the table below includes additional restrictions on the formats of these values to which device implementations MUST conform.

Parameter	Comments
android.os.Build.VERSION.RELEASE	The version of the currently-executing Android system, in human-readable format. This field MUST have one of the string values defined in [Resources, 7].
android.os.Build.VERSION.SDK	The version of the currently-executing Android system, in a format accessible to third-party application code. For Android 4.2, this field MUST have the integer value 17.
android.os.Build.VERSION.SDK_INT	The version of the currently-executing Android system, in a format accessible to third-party application code. For Android 4.2, this field MUST have the integer value 17.
android.os.Build.VERSION.INCREMENTAL	A value chosen by the device implementer designating the specific build of the currently-executing Android system, in human-readable format. This value MUST NOT be re-used for different builds made available to end users. A typical use of this field is to indicate which build number or source-control change identifier was used to generate the build. There are no requirements on the specific format of this field, except that it MUST NOT be null or the empty string ("").
android.os.Build.BOARD	A value chosen by the device implementer identifying the specific internal hardware used by the device, in human-readable format. A possible use of this field is to indicate the specific revision of the board powering the device. The value of this field MUST be encodable as 7-bit ASCII and match the regular expression "^[a-zA-Z0-9.,_-]+$".
android.os.Build.BRAND	A value chosen by the device implementer identifying the name of the company, organization, individual, etc. who produced the device, in human-readable format. A possible use of this field is to indicate the OEM and/or carrier who sold the device. The value of this field MUST be encodable as 7-bit ASCII and match the regular expression "^[a-zA-Z0-9.,_-]+$".
android.os.Build.CPU_ABI	The name of the instruction set (CPU type + ABI convention) of native code. See Section 3.3: Native API Compatibility.
android.os.Build.CPU_ABI2	The name of the second instruction set (CPU type + ABI convention) of native code. See Section 3.3: Native API Compatibility.
android.os.Build.DEVICE	A value chosen by the device implementer identifying the specific configuration or revision of the body (sometimes called "industrial design") of the device. The value of this field MUST be encodable as 7-bit ASCII and match the regular expression "^[a-zA-Z0-9.,_-]+$".
android.os.Build.FINGERPRINT	A string that uniquely identifies this build. It SHOULD be reasonably human-readable. It MUST follow this template: $(BRAND)/$(PRODUCT)/$(DEVICE):$(VERSION.RELEASE)/$(ID)/$(VERSION.INCREMENTAL):$(TYPE)/$(TAGS) For example: acme/mydevice/generic:4.2/JRN53/3359:userdebug/test-keys The fingerprint MUST NOT include whitespace characters. If other fields included in the template above have whitespace characters, they MUST be replaced in the build fingerprint with another character, such as the underscore ("_") character. The value of this field MUST be encodable as 7-bit ASCII.
android.os.Build.HARDWARE	The name of the hardware (from the kernel command line or /proc). It SHOULD be reasonably human-readable. The value of this field MUST be encodable as 7-bit ASCII and match the regular expression "^[a-zA-Z0-9.,_-]+$".
android.os.Build.HOST	A string that uniquely identifies the host the build was built on, in human readable format. There are no requirements on the specific format of this field, except that it MUST NOT be null or the empty string ("").
android.os.Build.ID	An identifier chosen by the device implementer to refer to a specific release, in human readable format. This field can be the same as android.os.Build.VERSION.INCREMENTAL, but SHOULD be a value sufficiently meaningful for end users to distinguish between software builds. The value of this field MUST be encodable as 7-bit ASCII and match the regular expression "^[a-zA-Z0-9.,_-]+$".
android.os.Build.MANUFACTURER	The trade name of the Original Equipment Manufacturer (OEM) of the product. There are no requirements on the specific format of this field, except that it MUST NOT be null or the empty string ("").
android.os.Build.MODEL	A value chosen by the device implementer containing the name of the device as known to the end user. This SHOULD be the same name under which the device is marketed and sold to end users. There are no requirements on the specific format of this field, except that it MUST NOT be null or the empty string ("").
android.os.Build.PRODUCT	A value chosen by the device implementer containing the development name or code name of the product (SKU). MUST be human-readable, but is not necessarily intended for view by end users. The value of this field MUST be encodable as 7-bit ASCII and match the regular expression "^[a-zA-Z0-9.,_-]+$".
android.os.Build.SERIAL	A hardware serial number, if available. The value of this field MUST be encodable as 7-bit ASCII and match the regular expression "^([a-zA-Z0-9]{0,20})$".
android.os.Build.TAGS	A comma-separated list of tags chosen by the device implementer that further distinguish the build. For example, "unsigned,debug". The value of this field MUST be encodable as 7-bit ASCII and match the regular expression "^[a-zA-Z0-9.,_-]+$".
android.os.Build.TIME	A value representing the timestamp of when the build occurred.
android.os.Build.TYPE	A value chosen by the device implementer specifying the runtime configuration of the build. This field SHOULD have one of the values corresponding to the three typical Android runtime configurations: "user", "userdebug", or "eng". The value of this field MUST be encodable as 7-bit ASCII and match the regular expression "^[a-zA-Z0-9.,_-]+$".
android.os.Build.USER	A name or user ID of the user (or automated user) that generated the build. There are no requirements on the specific format of this field, except that it MUST NOT be null or the empty string ("").

3.2.3. Intent Compatibility

Device implementations MUST honor Android's loose-coupling Intent system, as described in the sections below. By "honored", it is meant that the device implementer MUST provide an Android Activity or Service that specifies a matching Intent filter and binds to and implements correct behavior for each specified Intent pattern.

3.2.3.1. Core Application Intents

The Android upstream project defines a number of core applications, such as contacts, calendar, photo gallery, music player, and so on. Device implementers MAY replace these applications with alternative versions.

However, any such alternative versions MUST honor the same Intent patterns provided by the upstream project. For example, if a device contains an alternative music player, it must still honor the Intent pattern issued by third-party applications to pick a song.

The following applications are considered core Android system applications:

• Desk Clock
• Browser
• Calendar
• Contacts
• Gallery
• GlobalSearch
• Launcher
• Music
• Settings

The core Android system applications include various Activity, or Service components that are considered "public". That is, the attribute "android:exported" may be absent, or may have the value "true".

For every Activity or Service defined in one of the core Android system apps that is not marked as non-public via an android:exported attribute with the value "false", device implementations MUST include a component of the same type implementing the same Intent filter patterns as the core Android system app.

In other words, a device implementation MAY replace core Android system apps; however, if it does, the device implementation MUST support all Intent patterns defined by each core Android system app being replaced.

3.2.3.2. Intent Overrides

As Android is an extensible platform, device implementations MUST allow each Intent pattern referenced in Section 3.2.3.2 to be overridden by third-party applications. The upstream Android open source implementation allows this by default; device implementers MUST NOT attach special privileges to system applications' use of these Intent patterns, or prevent third-party applications from binding to and assuming control of these patterns. This prohibition specifically includes but is not limited to disabling the "Chooser" user interface which allows the user to select between multiple applications which all handle the same Intent pattern.

However, device implementations MAY provide default activities for specific URI patterns (eg. http://play.google.com) if the default activity provides a more specific filter for the data URI. For example, an intent filter specifying the data URI "http://www.android.com" is more specific than the browser filter for "http://". Device implementations MUST provide a user interface for users to modify the default activity for intents.

3.2.3.3. Intent Namespaces

Device implementations MUST NOT include any Android component that honors any new Intent or Broadcast Intent patterns using an ACTION, CATEGORY, or other key string in the android.* or com.android.* namespace. Device implementers MUST NOT include any Android components that honor any new Intent or Broadcast Intent patterns using an ACTION, CATEGORY, or other key string in a package space belonging to another organization. Device implementers MUST NOT alter or extend any of the Intent patterns used by the core apps listed in Section 3.2.3.1. Device implementations MAY include Intent patterns using namespaces clearly and obviously associated with their own organization.

This prohibition is analogous to that specified for Java language classes in Section 3.6.

3.2.3.4. Broadcast Intents

Third-party applications rely on the platform to broadcast certain Intents to notify them of changes in the hardware or software environment. Android-compatible devices MUST broadcast the public broadcast Intents in response to appropriate system events. Broadcast Intents are described in the SDK documentation.

3.3. Native API Compatibility

3.3.1 Application Binary Interfaces

Managed code running in Dalvik can call into native code provided in the application .apk file as an ELF .so file compiled for the appropriate device hardware architecture. As native code is highly dependent on the underlying processor technology, Android defines a number of Application Binary Interfaces (ABIs) in the Android NDK, in the file docs/CPU-ARCH-ABIS.html. If a device implementation is compatible with one or more defined ABIs, it SHOULD implement compatibility with the Android NDK, as below.

If a device implementation includes support for an Android ABI, it:

• MUST include support for code running in the managed environment to call into native code, using the standard Java Native Interface (JNI) semantics.
• MUST be source-compatible (i.e. header compatible) and binary-compatible (for the ABI) with each required library in the list below
• MUST accurately report the native Application Binary Interface (ABI) supported by the device, via the android.os.Build.CPU_ABI API
• MUST report only those ABIs documented in the latest version of the Android NDK, in the file docs/CPU-ARCH-ABIS.txt
• SHOULD be built using the source code and header files available in the upstream Android open source project

The following native code APIs MUST be available to apps that include native code:

• libc (C library)
• libm (math library)
• Minimal support for C++
• JNI interface
• liblog (Android logging)
• libz (Zlib compression)
• libdl (dynamic linker)
• libGLESv1_CM.so (OpenGL ES 1.0)
• libGLESv2.so (OpenGL ES 2.0)
• libEGL.so (native OpenGL surface management)
• libjnigraphics.so
• libOpenSLES.so (OpenSL ES 1.0.1 audio support)
• libOpenMAXAL.so (OpenMAX AL 1.0.1 support)
• libandroid.so (native Android activity support)
• Support for OpenGL, as described below

Note that future releases of the Android NDK may introduce support for additional ABIs. If a device implementation is not compatible with an existing predefined ABI, it MUST NOT report support for any ABI at all.

Native code compatibility is challenging. For this reason, it should be repeated that device implementers are VERY strongly encouraged to use the upstream implementations of the libraries listed above to help ensure compatibility.

3.4. Web Compatibility

3.4.1. WebView Compatibility

The Android Open Source implementation uses the WebKit rendering engine to implement the android.webkit.WebView. Because it is not feasible to develop a comprehensive test suite for a web rendering system, device implementers MUST use the specific upstream build of WebKit in the WebView implementation. Specifically:

• Device implementations' android.webkit.WebView implementations MUST be based on the 534.30 WebKit build from the upstream Android Open Source tree for Android 4.2. This build includes a specific set of functionality and security fixes for the WebView. Device implementers MAY include customizations to the WebKit implementation; however, any such customizations MUST NOT alter the behavior of the WebView, including rendering behavior.
• The user agent string reported by the WebView MUST be in this format:
  Mozilla/5.0 (Linux; U; Android $(VERSION); $(LOCALE); $(MODEL) Build/$(BUILD)) AppleWebKit/534.30 (KHTML, like Gecko) Version/4.2 Mobile Safari/534.30
  • The value of the $(VERSION) string MUST be the same as the value for android.os.Build.VERSION.RELEASE
  • The value of the $(LOCALE) string SHOULD follow the ISO conventions for country code and language, and SHOULD refer to the current configured locale of the device
  • The value of the $(MODEL) string MUST be the same as the value for android.os.Build.MODEL
  • The value of the $(BUILD) string MUST be the same as the value for android.os.Build.ID
  • Device implementations MAY omit Mobile in the user agent string

The WebView component SHOULD include support for as much of HTML5 [Resources, 11] as possible. Minimally, device implementations MUST support each of these APIs associated with HTML5 in the WebView:

• application cache/offline operation [Resources, 12]
• the <video> tag [Resources, 13]
• geolocation [Resources, 14]

Additionally, device implementations MUST support the HTML5/W3C webstorage API [Resources, 15], and SHOULD support the HTML5/W3C IndexedDB API [Resources, 16]. Note that as the web development standards bodies are transitioning to favor IndexedDB over webstorage, IndexedDB is expected to become a required component in a future version of Android.

HTML5 APIs, like all JavaScript APIs, MUST be disabled by default in a WebView, unless the developer explicitly enables them via the usual Android APIs.

3.4.2. Browser Compatibility

Device implementations MUST include a standalone Browser application for general user web browsing. The standalone Browser MAY be based on a browser technology other than WebKit. However, even if an alternate Browser application is used, the android.webkit.WebView component provided to third-party applications MUST be based on WebKit, as described in Section 3.4.1.

Implementations MAY ship a custom user agent string in the standalone Browser application.

The standalone Browser application (whether based on the upstream WebKit Browser application or a third-party replacement) SHOULD include support for as much of HTML5 [Resources, 11] as possible. Minimally, device implementations MUST support each of these APIs associated with HTML5:

• application cache/offline operation [Resources, 12]
• the <video> tag [Resources, 13]
• geolocation [Resources, 14]

Additionally, device implementations MUST support the HTML5/W3C webstorage API [Resources, 15], and SHOULD support the HTML5/W3C IndexedDB API [Resources, 16]. Note that as the web development standards bodies are transitioning to favor IndexedDB over webstorage, IndexedDB is expected to become a required component in a future version of Android.

3.5. API Behavioral Compatibility

The behaviors of each of the API types (managed, soft, native, and web) must be consistent with the preferred implementation of the upstream Android open source project [Resources, 3]. Some specific areas of compatibility are:

• Devices MUST NOT change the behavior or semantics of a standard Intent
• Devices MUST NOT alter the lifecycle or lifecycle semantics of a particular type of system component (such as Service, Activity, ContentProvider, etc.)
• Devices MUST NOT change the semantics of a standard permission

The above list is not comprehensive. The Compatibility Test Suite (CTS) tests significant portions of the platform for behavioral compatibility, but not all. It is the responsibility of the implementer to ensure behavioral compatibility with the Android Open Source Project. For this reason, device implementers SHOULD use the source code available via the Android Open Source Project where possible, rather than re-implement significant parts of the system.

3.6. API Namespaces

Android follows the package and class namespace conventions defined by the Java programming language. To ensure compatibility with third-party applications, device implementers MUST NOT make any prohibited modifications (see below) to these package namespaces:

• java.*
• javax.*
• sun.*
• android.*
• com.android.*

Prohibited modifications include:

• Device implementations MUST NOT modify the publicly exposed APIs on the Android platform by changing any method or class signatures, or by removing classes or class fields.
• Device implementers MAY modify the underlying implementation of the APIs, but such modifications MUST NOT impact the stated behavior and Java-language signature of any publicly exposed APIs.
• Device implementers MUST NOT add any publicly exposed elements (such as classes or interfaces, or fields or methods to existing classes or interfaces) to the APIs above.

A "publicly exposed element" is any construct which is not decorated with the "@hide" marker as used in the upstream Android source code. In other words, device implementers MUST NOT expose new APIs or alter existing APIs in the namespaces noted above. Device implementers MAY make internal-only modifications, but those modifications MUST NOT be advertised or otherwise exposed to developers.

Device implementers MAY add custom APIs, but any such APIs MUST NOT be in a namespace owned by or referring to another organization. For instance, device implementers MUST NOT add APIs to the com.google.* or similar namespace; only Google may do so. Similarly, Google MUST NOT add APIs to other companies' namespaces. Additionally, if a device implementation includes custom APIs outside the standard Android namespace, those APIs MUST be packaged in an Android shared library so that only apps that explicitly use them (via the <uses-library> mechanism) are affected by the increased memory usage of such APIs.

If a device implementer proposes to improve one of the package namespaces above (such as by adding useful new functionality to an existing API, or adding a new API), the implementer SHOULD visit source.android.com and begin the process for contributing changes and code, according to the information on that site.

Note that the restrictions above correspond to standard conventions for naming APIs in the Java programming language; this section simply aims to reinforce those conventions and make them binding through inclusion in this compatibility definition.

3.7. Virtual Machine Compatibility

Device implementations MUST support the full Dalvik Executable (DEX) bytecode specification and Dalvik Virtual Machine semantics [Resources, 17].

Device implementations MUST configure Dalvik to allocate memory in accordance with the upstream Android platform, and as specified by the following table. (See Section 7.1.1 for screen size and screen density definitions.)

Note that memory values specified below are considered minimum values, and device implementations MAY allocate more memory per application.

Screen Size	Screen Density	Application Memory
small / normal / large	ldpi / mdpi	16MB
small / normal / large	tvdpi / hdpi	32MB
small / normal / large	xhdpi	64MB
xlarge	mdpi	32MB
xlarge	tvdpi / hdpi	64MB
xlarge	xhdpi	128MB

3.8. User Interface Compatibility

3.8.1. Widgets

Android defines a component type and corresponding API and lifecycle that allows applications to expose an "AppWidget" to the end user [Resources, 18]. The Android Open Source reference release includes a Launcher application that includes user interface affordances allowing the user to add, view, and remove AppWidgets from the home screen.

Device implementations MAY substitute an alternative to the reference Launcher (i.e. home screen). Alternative Launchers SHOULD include built-in support for AppWidgets, and expose user interface affordances to add, configure, view, and remove AppWidgets directly within the Launcher. Alternative Launchers MAY omit these user interface elements; however, if they are omitted, the device implementation MUST provide a separate application accessible from the Launcher that allows users to add, configure, view, and remove AppWidgets.

Device implementations MUST be capable of rendering widgets that are 4 x 4 in the standard grid size. (See the App Widget Design Guidelines in the Android SDK documentation [Resources, 18] for details.

3.8.2. Notifications

Android includes APIs that allow developers to notify users of notable events [Resources, 19], using hardware and software features of the device.

Some APIs allow applications to perform notifications or attract attention using hardware, specifically sound, vibration, and light. Device implementations MUST support notifications that use hardware features, as described in the SDK documentation, and to the extent possible with the device implementation hardware. For instance, if a device implementation includes a vibrator, it MUST correctly implement the vibration APIs. If a device implementation lacks hardware, the corresponding APIs MUST be implemented as no-ops. Note that this behavior is further detailed in Section 7.

Additionally, the implementation MUST correctly render all resources (icons, sound files, etc.) provided for in the APIs [Resources, 20], or in the Status/System Bar icon style guide [Resources, 21]. Device implementers MAY provide an alternative user experience for notifications than that provided by the reference Android Open Source implementation; however, such alternative notification systems MUST support existing notification resources, as above.

Android 4.2 includes support for rich notifications, such as interactive Views for ongoing notifications. Device implementations MUST properly display and execute rich notifications, as documented in the Android APIs.

3.8.3. Search

Android includes APIs [Resources, 22] that allow developers to incorporate search into their applications, and expose their application's data into the global system search. Generally speaking, this functionality consists of a single, system-wide user interface that allows users to enter queries, displays suggestions as users type, and displays results. The Android APIs allow developers to reuse this interface to provide search within their own apps, and allow developers to supply results to the common global search user interface.

Device implementations MUST include a single, shared, system-wide search user interface capable of real-time suggestions in response to user input. Device implementations MUST implement the APIs that allow developers to reuse this user interface to provide search within their own applications. Device implementations MUST implement the APIs that allow third-party applications to add suggestions to the search box when it is run in global search mode. If no third-party applications are installed that make use of this functionality, the default behavior SHOULD be to display web search engine results and suggestions.

3.8.4. Toasts

Applications can use the "Toast" API (defined in [Resources, 23]) to display short non-modal strings to the end user, that disappear after a brief period of time. Device implementations MUST display Toasts from applications to end users in some high-visibility manner.

3.8.5. Themes

Android provides "themes" as a mechanism for applications to apply styles across an entire Activity or application. Android 4.2 includes a "Holo" or "holographic" theme as a set of defined styles for application developers to use if they want to match the Holo theme look and feel as defined by the Android SDK [Resources, 24]. Device implementations MUST NOT alter any of the Holo theme attributes exposed to applications [Resources, 25].

Android 4.2 includes a new "Device Default" theme as a set of defined styles for application developers to use if they want to match the look and feel of the device theme as defined by the device implementer. Device implementations MAY modify the DeviceDefault theme attributes exposed to applications [Resources, 25].

3.8.6. Live Wallpapers

Android defines a component type and corresponding API and lifecycle that allows applications to expose one or more "Live Wallpapers" to the end user [Resources, 26]. Live Wallpapers are animations, patterns, or similar images with limited input capabilities that display as a wallpaper, behind other applications.

Hardware is considered capable of reliably running live wallpapers if it can run all live wallpapers, with no limitations on functionality, at a reasonable framerate with no adverse affects on other applications. If limitations in the hardware cause wallpapers and/or applications to crash, malfunction, consume excessive CPU or battery power, or run at unacceptably low frame rates, the hardware is considered incapable of running live wallpaper. As an example, some live wallpapers may use an Open GL 1.0 or 2.0 context to render their content. Live wallpaper will not run reliably on hardware that does not support multiple OpenGL contexts because the live wallpaper use of an OpenGL context may conflict with other applications that also use an OpenGL context.

Device implementations capable of running live wallpapers reliably as described above SHOULD implement live wallpapers. Device implementations determined to not run live wallpapers reliably as described above MUST NOT implement live wallpapers.

3.8.7. Recent Application Display

The upstream Android 4.2 source code includes a user interface for displaying recent applications using a thumbnail image of the application's graphical state at the moment the user last left the application. Device implementations MAY alter or eliminate this user interface; however, a future version of Android is planned to make more extensive use of this functionality. Device implementations are strongly encouraged to use the upstream Android 4.2 user interface (or a similar thumbnail-based interface) for recent applications, or else they may not be compatible with a future version of Android.

3.8.8. Input Management Settings

Android 4.2 includes support for Input Management Engines. The Android 4.2 APIs allow custom app IMEs to specify user-tunable settings. Device implementations MUST include a way for the user to access IME settings at all times when an IME that provides such user settings is displayed.

3.8.9. Lock and Home Screen Widgets

Android 4.2 includes support for application widgets that users can embed in the home screen or the lock screen (See the App Widget Design Guidelines in the Android SDK documentation [Resources, 69] for details). Application widgets allow quick access to application data and services without launching a new activity. Widgets declare support for usage on the home screen or the lock screen by declaring the android:widgetCategory manifest tag that tells the system where the widget can be placed. Specifically, device implementations MUST meet the following requirements.

• Device implementations MUST support application widgets on the home screen.
• Device implementations SHOULD support lock screen. If device implementations include support for lock screen then device implementations MUST support application widgets on the lock screen.

3.8.10. Lock Screen Media Remote Control

Android 4.2 includes support for Remote Control API that lets media applications integrate with playback controls that are displayed in a remote view like the device lock screen[Resources, 74]. Device implementations MUST include support for embedding remote controls in the device lock screen.

3.8.11. Dreams

Android 4.2 includes support for interactive screensavers called Dreams [Resources, 76]. Dreams allows users to interact with applications when a charging device is idle, or docked in a desk dock. Device implementations MUST include support for Dreams and provide a settings option for users to configure Dreams.

3.9 Device Administration

Android 4.2 includes features that allow security-aware applications to perform device administration functions at the system level, such as enforcing password policies or performing remote wipe, through the Android Device Administration API [Resources, 27]. Device implementations MUST provide an implementation of the DevicePolicyManager class [Resources, 28], and SHOULD support the full range of device administration policies defined in the Android SDK documentation [Resources, 27].

Note: while some of the requirements outlined above are stated as "SHOULD" for Android 4.2, device implementations that support lock screen MUST support device policies to manage widgets on the lock screen as defined in the Android SDK documentation [Resources, 27].

Note: while some of the requirements outlined above are stated as "SHOULD" for Android 4.2, the Compatibility Definition for a future version is planned to change these to "MUST". That is, these requirements are optional in Android 4.2 but will be required by a future version. Existing and new devices that run Android 4.2 are very strongly encouraged to meet these requirements in Android 4.2, or they will not be able to attain Android compatibility when upgraded to the future version.

3.10 Accessibility

Android 4.2 provides an accessibility layer that helps users with disabilities to navigate their devices more easily. In addition, Android 4.2 provides platform APIs that enable accessibility service implementations to receive callbacks for user and system events and generate alternate feedback mechanisms, such as text-to-speech, haptic feedback, and trackball/d-pad navigation [Resources, 29]. Device implementations MUST provide an implementation of the Android accessibility framework consistent with the default Android implementation. Specifically, device implementations MUST meet the following requirements.

• Device implementations MUST support third party accessibility service implementations through the android.accessibilityservice APIs [Resources, 30].
• Device implementations MUST generate AccessibilityEvents and deliver these events to all registered AccessibilityService implementations in a manner consistent with the default Android implementation.
• Device implementations MUST provide a user-accessible mechanism to enable and disable accessibility services, and MUST display this interface in response to the android.provider.Settings.ACTION_ACCESSIBILITY_SETTINGS intent.

Additionally, device implementations SHOULD provide an implementation of an accessibility service on the device, and SHOULD provide a mechanism for users to enable the accessibility service during device setup. An open source implementation of an accessibility service is available from the Eyes Free project [Resources, 31].

3.11 Text-to-Speech

Android 4.2 includes APIs that allow applications to make use of text-to-speech (TTS) services, and allows service providers to provide implementations of TTS services [Resources, 32]. Device implementations MUST meet these requirements related to the Android TTS framework:

• Device implementations MUST support the Android TTS framework APIs and SHOULD include a TTS engine supporting the languages available on the device. Note that the upstream Android open source software includes a full-featured TTS engine implementation.
• Device implementations MUST support installation of third-party TTS engines.
• Device implementations MUST provide a user-accessible interface that allows users to select a TTS engine for use at the system level.

4. Application Packaging Compatibility

Device implementations MUST install and run Android ".apk" files as generated by the "aapt" tool included in the official Android SDK [Resources, 33].

Devices implementations MUST NOT extend either the .apk [Resources, 34], Android Manifest [Resources, 35], Dalvik bytecode [Resources, 17], or renderscript bytecode formats in such a way that would prevent those files from installing and running correctly on other compatible devices. Device implementers SHOULD use the reference upstream implementation of Dalvik, and the reference implementation's package management system.

5. Multimedia Compatibility

Device implementations MUST include at least one form of audio output, such as speakers, headphone jack, external speaker connection, etc.

5.1. Media Codecs

Device implementations MUST support the core media formats specified in the Android SDK documentation [