API Level: 12
For developers, the Android 3.1 platform is available as a downloadable component for the Android SDK. The downloadable platform includes an Android library and system image, as well as a set of emulator skins and more. The downloadable platform includes no external libraries.
To get started developing or testing against Android 3.1, use the Android SDK Manager to download the platform into your SDK. For more information, see Adding SDK Components. If you are new to Android, download the SDK Starter Package first.
For a high-level introduction to Android 3.1, see the Platform Highlights.
Reminder: If you've already published an Android application, please test and optimize your application on Android 3.0 and Android 3.1 as soon as possible. You should do so to be sure your application provides the best experience possible on the latest Android-powered devices. For information about what you can do, read Optimizing Apps for Android 3.0.
To determine what revision of the Android 3.1 platform you have installed, refer to the "Installed Packages" listing in the Android SDK and AVD Manager.
Android 3.1, Revision 3 (July 2011)
Requires SDK Tools r12 or higher.
Improvements to the platform's rendering library to support the visual layout editor in the ADT Eclipse plugin. This revision allows for more drawing features in ADT and fixes several bugs in the previous rendering library. It also unlocks several editor features that were added in ADT 12.
Android 3.1, Revision 2 (May 2011)
Requires SDK Tools r11 or higher.
Fixes an issue with the visual layout editor rendering library that prevented Android 3.1 from running in ADT.
Android 3.1, Revision 1 (May 2011)
Requires SDK Tools r11 or higher.
The sections below provide a technical overview of what's new for developers in Android 3.1, including new features and changes in the framework API since the previous version.
Android 3.1 introduces powerful new APIs for integrating connected peripherals with applications running on the platform. The APIs are based on a USB (Universal Serial Bus) stack and services that are built into the platform, including support for both USB host and device interactions. Using the APIs, developers can create applications that are able to discover, communicate with, and manage a variety of device types connected over USB.
The stack and APIs distinguish two basic types of USB hardware, based on whether the Android-powered device is acting as host or the external hardware is acting as host:
For both types — USB devices and USB accessories — the platform's USB APIs support discovery by intent broadcast when attached or detached, as well as standard interfaces, endpoints, and transfer modes (control, bulk, and interrupt).
The USB APIs are available in the package android.hardware.usb. The
central class is UsbManager, which provides
helper methods for identifying and communicating with
both USB devices and USB accessories. Applications can acquire an instance of
UsbManager and then query for the list of attached
devices or accessories and then communicate with or manage them.
UsbManager also declares intent actions that the
system broadcasts, to announce when a USB device or accessory is attached or
detached.
Other classes include:
UsbDevice, a class representing external
hardware connected as a USB device (with the Android-powered device acting as
host).UsbAccessory, representing external hardware
connected as the USB host (with the Android-powered device acting as a USB
device).UsbInterface and UsbEndpoint, which provide access to standard USB
interfaces and endpoints for a device.UsbDeviceConnection and UsbRequest, for sending and receiving data and control
messages to or from a USB device, sychronously and asynchronously.
UsbConstants, which provides constants for
declaring endpoint types, device classes, and so on.Note that although the USB stack is built into the platform, actual support for USB host and open accessory modes on specific devices is determined by their manufacturers. In particular, host mode relies on appropriate USB controller hardware in the Android-powered device.
Additionally, developers can request filtering on Android Market, such that their applications are not availabe to users whose devices do not provide the appropriate USB support. To request filtering, add one or both of the elements below to the application manifest, as appropriate:
<uses-feature
android:name="android.hardware.usb.host"
android:required="true">
<uses-feature
android:name="android.hardware.usb.accessory"
android:required="true">
For complete information about how to develop applications that interact with USB accessories, please see the developer documentation.
To look at sample applications that use the USB host API, see ADB Test and Missile Launcher
Android 3.1 exposes a new MTP API that lets applications interact directly with connected cameras and other PTP devices. The new API makes it easy for an application to receive notifications when devices are attached and removed, manage files and storage on those devices, and transfer files and metadata to and from them. The MTP API implements the PTP (Picture Transfer Protocol) subset of the MTP (Media Transfer Protocol) specification.
The MTP API is available in the android.mtp package and provides
these classes:
MtpDevice encapsulates an MTP device that is
connected over the USB host bus. An application can instantiate an object of
this type and then use its methods to get information about the device and
objects stored on it, as well as opening the connection and transferring data.
Some of the methods include:
getObjectHandles() returns a list of handles for all objects on the device that
match a specified format and parent. To get information about an object, an
application can pass a handle to getObjectInfo().importFile() lets an application copy data for an object to a file in external
storage. This call may block for an arbitrary amount of time depending on the
size of the data and speed of the devices, so should be made from a spearate
thread.open()
lets an application open a connected MTP/PTP device. getThumbnail() returns
the thumbnail of the object as a byte array. MtpStorageInfo holds information about about a storage
unit on an MTP device, corresponding to the StorageInfo Dataset described in
section 5.2.2 of the MTP specification. Methods in the class let an application
get a storage unit’s description string, free space, maximum storage capacity,
storage ID, and volume identifier.MtpDeviceInfo holds information about an MTP device
corresponding to the DeviceInfo Dataset described in section 5.1.1 of the MTP
specification. Methods in the class let applications get a device’s
manufacturer, model, serial number, and version.MtpObjectInfo holds information about an object stored
on an MTP device, corresponding to the ObjectInfo Dataset described in section
5.3.1 of the MTP specification. Methods in the class let applications get an
object’s size, data format, association type, creation date, and thumbnail
information.MtpConstants provides constants for declaring MTP file
format codes, association type, and protection status.Android 3.1 extends the input subsystem to support new input devices and new types of motion events, across all views and windows. Developers can build on these capabilities to let users interact with their applications using mice, trackballs, joysticks, gamepads, and other devices, in addition to keyboards and touchscreens.
For handling mouse, scrollwheel, and trackball input, the platform supports two new motion event actions:
ACTION_SCROLL, which describes the pointer
location at which a non-touch scroll motion, such as from a mouse scroll wheel,
took place. In the MotionEvent, the value of the AXIS_HSCROLL and AXIS_VSCROLL axes specify the relative scroll
movement. ACTION_HOVER_MOVE, reports the current
position of the mouse when no buttons are pressed, as well as any intermediate
points since the last HOVER_MOVE event. Hover enter and exit
notifications are not yet supported.To support joysticks and gamepads, the InputDevice class
includes these new input device sources:
SOURCE_CLASS_JOYSTICK — the source
device has joystick axes.SOURCE_CLASS_BUTTON — the source
device has buttons or keys.SOURCE_GAMEPAD — the source device
has gamepad buttons such as KEYCODE_BUTTON_A
or KEYCODE_BUTTON_B. Implies
SOURCE_CLASS_BUTTONSOURCE_JOYSTICK — the source device
has joystick axes. Implies SOURCE_CLASS_JOYSTICK.To describe motion events from these new sources, as well as those from mice
and trackballs, the platform now defines axis codes on MotionEvent, similar to how it defines key codes on KeyEvent. New axis codes for joysticks
and game controllers include
AXIS_HAT_X, AXIS_HAT_Y, AXIS_RTRIGGER, AXIS_ORIENTATION, AXIS_THROTTLE, and many others.
Existing MotionEvent axes are represented by AXIS_X, AXIS_Y,
AXIS_PRESSURE, AXIS_SIZE, AXIS_TOUCH_MAJOR, AXIS_TOUCH_MINOR, AXIS_TOOL_MAJOR, AXIS_TOOL_MINOR, and AXIS_ORIENTATION.
Additionally, MotionEvent defines a number of generic
axis codes that are used when the framework does not know how to map a
particular axis. Specific devices can use the generic axis codes to pass custom
motion data to applications. For a full list of axes and their intended
interpretations, see the MotionEvent class documentation.
The platform provides motion events to applications in batches, so a single
event may contain a current position and multiple so-called historical movements.
Applications should use getHistorySize() to get
the number of historical samples, then retrieve and process all historical
samples in order using getHistoricalAxisValue(). After that, applications should process the current
sample using getAxisValue().
Some axes can be retrieved using special accessor methods. For example,
instead of calling getAxisValue(), applications can call getX(). Axes that have built-in accessors include AXIS_X, AXIS_Y,
AXIS_PRESSURE, AXIS_SIZE, AXIS_TOUCH_MAJOR, AXIS_TOUCH_MINOR, AXIS_TOOL_MAJOR, AXIS_TOOL_MINOR, and AXIS_ORIENTATION.
Each input device has a unique, system-assigned ID and may also provide
multiple sources. When a device provides multiple sources, more than one source
can provide axis data using the same axis. For example, a touch event coming
from the touch source uses the X axis for screen position data, while a joystick
event coming from the joystick source will use the X axis for the stick position
instead. For this reason, it's important for applications to interpret axis
values according to the source from which they originate. When handling a motion
event, applications should use methods on the InputDevice
class to determine the axes supported by a device or source. Specifically,
applications can use getMotionRanges() to query for all axes of a device or all axes of a given
source of the device. In both cases, the range information for axes returned in
the InputDevice.MotionRange object specifies the source for
each axis value.
Finally, since the motion events from joysticks, gamepads, mice, and
trackballs are not touch events, the platform adds a new callback method for
passing them to a View as "generic" motion events.
Specifically, it reports the non-touch motion events to
Views through a call to onGenericMotionEvent(), rather than to onTouchEvent().
The platform dispatches generic motion events differently, depending on the
event source class. SOURCE_CLASS_POINTER events
go to the View under the pointer, similar to how touch
events work. All others go to the currently focused View.
For example, this means a View must take focus in order to
receive joystick events. If needed, applications can handle these events at the
level of Activity or Dialog by implementing onGenericMotionEvent() there instead.
To look at a sample application that uses joystick motion events, see GameControllerInput and GameView.
Android 3.1 exposes an API to its built-in RTP (Real-time Transport Protocol) stack, which applications can use to manage on-demand or interactive data streaming. In particular, apps that provide VOIP, push-to-talk, conferencing, and audio streaming can use the API to initiate sessions and transmit or receive data streams over any available network.
The RTP API is available in the android.net.rtp package. Classes
include:
RtpStream, the base class of streams that send and
receive network packets with media payloads over RTP.AudioStream, a subclass of RtpStream that carries audio payloads over RTP.AudioGroup, a local audio hub for managing and
mixing the device speaker, microphone, and AudioStream.AudioCodec, which holds a collection of codecs that
you define for an AudioStream.To support audio conferencing and similar usages, an application instantiates two classes as endpoints for the stream:
AudioStream specifies a remote endpoint and consists
of network mapping and a configured AudioCodec.AudioGroup represents the local endpoint for one
or more AudioStreams. The AudioGroup mixes
all the AudioStreams and optionally interacts with the device
speaker and the microphone at the same time.The simplest usage involves a single remote endpoint and local endpoint.
For more complex usages, please refer to the limitations described for
AudioGroup.
To use the RTP API, applications must request permission from the user by
declaring <uses-permission
android:name="android.permission.INTERNET">
in their manifest files. To acquire the device microphone, the <uses-permission
android:name="android.permission.RECORD_AUDIO"> permission is also required.
Starting in Android 3.1, developers can make their homescreen widgets resizeable — horizontally, vertically, or on both axes. Users touch-hold a widget to show its resize handles, then drag the horizontal and/or vertical handles to change the size on the layout grid.
Developers can make any Home screen widget resizeable by defining a
resizeMode attribute in the widget's AppWidgetProviderInfo metadata. Values for the
resizeMode attribute include "horizontal", "vertical", and "none".
To declare a widget as resizeable horizontally and vertically, supply the value
"horizontal|vertical".
Here's an example:
<appwidget-provider xmlns:android="http://schemas.android.com/apk/res/android"
android:minWidth="294dp"
android:minHeight="72dp"
android:updatePeriodMillis="86400000"
android:previewImage="@drawable/preview"
android:initialLayout="@layout/example_appwidget"
android:configure="com.example.android.ExampleAppWidgetConfigure"
android:resizeMode="horizontal|vertical" >
</appwidget-provider>
For more information about Home screen widgets, see the App Widgets documentation.
ViewPropertyAnimator class provides a
convenient
way for developers to animate select properties on View objects. The class
automaties and optimizes the animation of the properties and makes it easier to
manage multiple simulataneous animations on a View object.
Using the ViewPropertyAnimator is straightforward. To animate properties for
a View, call animate() to
construct a ViewPropertyAnimator object for that View. Use the
methods on the ViewPropertyAnimator to specify what property to
animate and how to animate it. For example, to fade the View to transparent,
call alpha(0);. The ViewPropertyAnimator object
handles the details of configuring the underlying Animator class and starting it, then rendering the
animation.
getBackgroundColor() and
setBackgroundColor(int) methods let
you get/set the background color behind animations, for window animations
only. Currently the background must be black, with any desired alpha level.ViewAnimator
getAnimatedFraction()
method
lets you get the current animation fraction — the elapsed/interpolated
fraction used in the most recent frame update — from a ValueAnimator.buildLayer() method lets an application
force a View's layer to be created and the View rendered into it immediately.
For example, an application could use this method to render a View into its
layer before starting an animation. If the View is complex, rendering it into
the layer before starting the animation will avoid skipping frames.setCameraDistance(float) to set the distance from the
camera
to a View. This gives applications improved control over 3D transformations of
the View, such as rotations. getCalendarView() method
lets you get a CalendarView from a DatePicker
instance.View.OnAttachStateChangeListener lets you
receive
callbacks when a View is attached or detached from its window. Use addOnAttachStateChangeListener()
to add a listener and addOnAttachStateChangeListener() to remove it.setOnBreadCrumbClickListener(),
provides a hook to let
applications intercept fragment-breadcrumb clicks and take any action needed
before going to the backstack entry or fragment that was clicked. Fragment class, onInflate(attrs, savedInstanceState) is deprecated. Please use onInflate(activity, attrs, savedInstanceState) instead.EXTRA_NEW_SEARCH data key for ACTION_WEB_SEARCH intents lets you open a search in a
new browser tab, rather than in an existing one.textCursorDrawable.setDisplayedChild(viewId,
childIndex), is available in RemoteViews subclasses, to
let you set the child displayed in ViewAnimator and
AdapterViewAnimator subclasses such as AdapterViewFlipper, StackView, ViewFlipper, and ViewSwitcher.KeyEvent adds a range of generic keycodes to
accommodate gamepad buttons. The class also adds
isGamepadButton(int) and several other
helper methods for working with keycodes.setHasAlpha(boolean) lets an app indicate that
all of the pixels in a Bitmap are known to be opaque (false) or that some of the
pixels may contain non-opaque alpha values (true). Note, for some configs (such
as RGB_565) this call is ignored, since it does not support per-pixel alpha
values. This is meant as a drawing hint, as in some cases a bitmap that is known
to be opaque can take a faster drawing case than one that may have non-opaque
per-pixel alpha values. getByteCount() gets a Bitmap's size in
bytes.getGenerationId() lets an application find
out whether a Bitmap has been modified, such as for caching.sameAs(android.graphics.Bitmap) determines
whether a given Bitmap differs from the current Bitmap, in dimension,
configuration, or pixel data. Camera adds two new methods rotate() and setLocation() for
control of the
camera's location, for 3D transformations.To create a high-performance lock, pass WIFI_MODE_FULL_HIGH_PERF as the lock mode in a
call to createWifiLock().
TrafficStats. Applications can use the
methods to get UDP stats, packet count, TCP transmit/receive payload bytes and
segments for a given UID.getAuthUserName() and setAuthUserName().VISIBILITY_VISIBLE_NOTIFY_ONLY_COMPLETION
in the setNotificationVisibility() method of
the a request object.addCompletedDownload(), lets an application add a file to the
downloads database, so that it can be managed by the Downloads application.INTENT_EXTRAS_SORT_BY_SIZE to an ACTION_VIEW_DOWNLOADS intent.InputMethodSubtype adds the
method
containsExtraValueKey() to check whether an ExtraValue string is stored
for the subtype and
the method getExtraValueOf() to extract a specific key value from the ExtraValue hashmap.
Starting from Android 3.1, the system's package manager keeps track of applications that are in a stopped state and provides a means of controlling their launch from background processes and other applications.
Note that an application's stopped state is not the same as an Activity's stopped state. The system manages those two stopped states separately.
The platform defines two new intent flags that let a sender specify whether the Intent should be allowed to activate components in stopped application.
FLAG_INCLUDE_STOPPED_PACKAGES —
Include intent filters of stopped applications in the list of potential targets
to resolve against. FLAG_EXCLUDE_STOPPED_PACKAGES —
Exclude intent filters of stopped applications from the list of potential
targets.When neither or both of these flags is defined in an intent, the default behavior is to include filters of stopped applications in the list of potential targets.
Note that the system adds FLAG_EXCLUDE_STOPPED_PACKAGES to all broadcast
intents. It does this to prevent broadcasts from background services from
inadvertently or unnecessarily launching components of stoppped applications.
A background service or application can override this behavior by adding the
FLAG_INCLUDE_STOPPED_PACKAGES flag to broadcast
intents that should be allowed to activate stopped applications.
Applications are in a stopped state when they are first installed but are not yet launched and when they are manually stopped by the user (in Manage Applications).
The platform adds improved notification of application first launch and upgrades through two new intent actions:
ACTION_PACKAGE_FIRST_LAUNCH — Sent to
the installer package of an application when that application is first launched
(that is, the first time it is moved out of a stopped state). The data
contains the name of the package. ACTION_MY_PACKAGE_REPLACED — Notifies
an application that it was updated, with a new version was installed over
an existing version. This is only sent to the application that was replaced. It
does not contain any additional data. To receive it, declare an intent filter
for this action. You can use the intent to trigger code that helps get your
application back in proper running shape after an upgrade.
This intent is sent directly to the application, but only if the application was upgraded while it was in started state (not in a stopped state).
LruCache class lets your applications benefit
from efficient caching. Applications can use the class to reduce the time spent
computing or downloading data from the network, while maintaining a sensible
memory footprint for the cached data.LruCache is a cache
that holds strong references to a limited number of values. Each time a value is
accessed, it is moved to the head of a queue. When a value is added to a full
cache, the value at the end of that queue is evicted and may become eligible for
garbage collection.int
ParcelFileDescriptor using either of the new methods getFd() or detachFd(). CookieManager now supports cookies that use
the
file: URI scheme. You can use setAcceptFileSchemeCookies() to
enable/disable support for file scheme cookies, before constructing an instance
of WebView or CookieManager. In a
CookieManager instance, you can check whether file scheme cookies
is enabled by calling allowFileSchemeCookies().onReceivedLoginRequest()
notifies the host
application that an autologin request for the user was processed. The Browser application adds the following features to support web applications:
<video> tag. Playback is hardware-accelerated where possible.
The platform adds new hardware feature constants that developers can declare
in their application manifests, to inform external entities such as Android
Market of the application's requirement for new hardware capabilities supported
in this version of the platform. Developers declare these and other feature
constants in <uses-feature> manifest elements.
android.hardware.usb.accessory — The application uses the USB
API to communicate with external hardware devices connected over USB and
function as hosts.android.hardware.usb.host — The application uses the USB API
to communicate with external hardware devices connected over USB and function as
devices.Android Market filters applications based on features declared in <uses-feature> manifest elements. For more information about
declaring features in an application manifest, read Android Market
Filters.
For a detailed view of all API changes in Android 3.1 (API Level 12), see the API Differences Report.
The Android 3.1 platform delivers an updated version of the framework API. The Android 3.1 API is assigned an integer identifier — 12 — that is stored in the system itself. This identifier, called the "API Level", allows the system to correctly determine whether an application is compatible with the system, prior to installing the application.
To use APIs introduced in Android 3.1 in your application,
you need compile the application against the Android library that is provided in
the Android 3.1 SDK platform. Depending on your needs, you
might
also need to add an android:minSdkVersion="12"
attribute to the <uses-sdk> element in the application's
manifest.
For more information about how to use API Level, see the API Levels document.
The system image included in the downloadable platform provides these built-in applications:
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The system image included in the downloadable SDK platform provides a variety of built-in locales. In some cases, region-specific strings are available for the locales. In other cases, a default version of the language is used. The languages that are available in the Android 3.0 system image are listed below (with language_country/region locale descriptor).
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Note: The Android platform may support more locales than are included in the SDK system image. All of the supported locales are available in the Android Open Source Project.
The downloadable platform includes the following emulator skin:
For more information about how to develop an application that displays and functions properly on all Android-powered devices, see Supporting Multiple Screens.