page.title=Android 4.1 APIs excludeFromSuggestions=true sdk.platform.version=4.1 sdk.platform.apiLevel=16 @jd:body

In this document

  1. App Components
  2. Multimedia
  3. Camera
  4. Connectivity
  5. Accessibility
  6. Copy and Paste
  7. Renderscript
  8. Animation
  9. User Interface
  10. Input Framework
  11. Permissions
  12. Device Features

See also

  1. API Differences Report »

API Level: 16

Android 4.1 ({@link android.os.Build.VERSION_CODES#JELLY_BEAN}) is a progression of the platform that offers improved performance and enhanced user experience. It adds new features for users and app developers. This document provides an introduction to the most notable and useful new APIs for app developers.

As an app developer, Android 4.1 is available to you from the SDK Manager as a system image you can run in the Android emulator and an SDK platform against which you can build your app. You should download the system image and platform as soon as possible to build and test your app on Android 4.1.

App Components

Isolated services

By specifying {@code android:isolatedProcess="true"} in the {@code <service>} tag, your {@link android.app.Service} will run under its own isolated user ID process that has no permissions of its own.

Memory management

New {@link android.content.ComponentCallbacks2} constants such as {@link android.content.ComponentCallbacks2#TRIM_MEMORY_RUNNING_LOW} and {@link android.content.ComponentCallbacks2#TRIM_MEMORY_RUNNING_CRITICAL} provide foreground processes more information about memory state before the system calls {@link android.app.Activity#onLowMemory()}.

New {@link android.app.ActivityManager#getMyMemoryState} method allows you to retrieve the general memory state.

Content providers

A new method, {@link android.content.ContentResolver#acquireUnstableContentProviderClient acquireUnstableContentProviderClient()}, allows you to access a {@link android.content.ContentProviderClient} that may be "unstable" such that your app will not crash if the content provider does. It's useful when you are interacting with content providers in a separate app.

Live Wallpapers

New intent protocol to directly launch the live wallpaper preview activity so you can help users easily select your live wallpaper without forcing them to leave your app and navigate through the Home wallpaper picker.

To launch the live wallpaper picker, call {@link android.content.Context#startActivity startActivity()} with an {@link android.content.Intent} using {@link android.app.WallpaperManager#ACTION_CHANGE_LIVE_WALLPAPER} and an extra that specifies your live wallpaper {@link android.content.ComponentName} as a string in {@link android.app.WallpaperManager#EXTRA_LIVE_WALLPAPER_COMPONENT}.

App stack navigation

Android 4.1 makes it much easier to implement the proper design patterns for Up navigation. All you need to do is add the {@code android:parentActivityName} to each {@code <activity>} element in your manifest file. The system uses this information to open the appropriate activity when the user presses the Up button in the action bar (while also finishing the current activity). So if you declare the {@code android:parentActivityName} for each activity, you don't need the {@link android.app.Activity#onOptionsItemSelected onOptionsItemSelected()} method to handle click events on the action bar's app icon—the system now handles that event and resumes or creates the appropriate activity.

This is particularly powerful for scenarios in which the user enters one of your app's activities through a "deep dive" intent such as from a notification or an intent from different app (as described in the design guide for Navigating Between Apps). When the user enters your activity this way, your app may not naturally have a back stack of activities that can be resumed as the user navigates up. However, when you supply the {@code android:parentActivityName} attribute for your activities, the system recognizes whether or not your app already contains a back stack of parent activities and, if not, constructs a synthetic back stack that contains all parent activities.

Note: When the user enters a deep activity in your app and it creates a new task for your app, the system actually inserts the stack of parent activities into the task. As such, pressing the Back button also navigates back through the stack of parent activities.

When the system creates a synthetic back stack for your app, it builds a basic {@link android.content.Intent} to create a new instance of each parent activity. So there's no saved state for the parent activities the way you'd expect had the user naturally navigated through each activity. If any of the parent activities normally show a UI that's dependent on the user's context, that context information will be missing and you should deliver it when the user navigates back through the stack. For example, if the user is viewing an album in a music app, navigating up might bring them to an activity that lists all albums in a chosen music genre. In this case, if the stack must be created, it's necessary that you inform the parent activity what genre the current album belongs to so that the parent can display the proper list as if the user actually came from that activity. To deliver such information to a synthetic parent activity, you must override the {@link android.app.Activity#onPrepareNavigateUpTaskStack onPrepareNavigateUpTaskStack()} method. This provides you with a {@link android.app.TaskStackBuilder} object that the system created in order to synthesize the parent activities. The {@link android.app.TaskStackBuilder} contains {@link android.content.Intent} objects that the system uses to create each parent activity. In your implementation of {@link android.app.Activity#onPrepareNavigateUpTaskStack onPrepareNavigateUpTaskStack()}, you can modify the appropriate {@link android.content.Intent} to add extra data that the parent activity can use to determine the appropriate context and display the appropriate UI.

When the system creates the {@link android.app.TaskStackBuilder}, it adds the {@link android.content.Intent} objects that are used to create the parent activities in their logical order beginning from the top of the activity tree. So, the last {@link android.content.Intent} added to the internal array is the direct parent of the current activity. If you want to modify the {@link android.content.Intent} for the activity's parent, first determine the length of the array with {@link android.app.TaskStackBuilder#getIntentCount()} and pass that value to {@link android.app.TaskStackBuilder#editIntentAt editIntentAt()}.

If your app structure is more complex, there are several other APIs available that allow you to handle the behavior of Up navigation and fully customize the synthetic back stack. Some of the APIs that give you additional control include:

{@link android.app.Activity#onNavigateUp}
Override this to perform a custom action when the user presses the Up button.
{@link android.app.Activity#navigateUpTo}
Call this to finish the current activity and go to the activity indicated by the supplied {@link android.content.Intent}. If the activity exists in the back stack, but is not the closest parent, then all other activities between the current activity and the activity specified with the intent are finished as well.
{@link android.app.Activity#getParentActivityIntent}
Call this to get the {@link android.content.Intent} that will start the logical parent for the current activity.
{@link android.app.Activity#shouldUpRecreateTask}
Call this to query whether a synthetic back stack must be created in order to navigate up. Returns true if a synthetic stack must be created, false if the appropropriate stack already exists.
{@link android.app.Activity#finishAffinity}
Call this to finish the current activity and all parent activities with the same task affinity that are chained to the current activity. If you override the default behaviors such as {@link android.app.Activity#onNavigateUp}, you should call this method when you create a synthetic back stack upon Up navigation.
{@link android.app.Activity#onCreateNavigateUpTaskStack onCreateNavigateUpTaskStack}
Override this if you need to fully control how the synthetic task stack is created. If you want to simply add some extra data to the intents for your back stack, you should instead override {@link android.app.Activity#onPrepareNavigateUpTaskStack onPrepareNavigateUpTaskStack()}

However, most apps don't need to use these APIs or implement {@link android.app.Activity#onPrepareNavigateUpTaskStack onPrepareNavigateUpTaskStack()}, but can can achieve the correct behavior simply by adding {@code android:parentActivityName} to each {@code <activity>} element.

Multimedia

Media codecs

The {@link android.media.MediaCodec} class provides access to low-level media codecs for encoding and decoding your media. You can instantiate a {@link android.media.MediaCodec} by calling {@link android.media.MediaCodec#createEncoderByType createEncoderByType()} to encode media or call {@link android.media.MediaCodec#createDecoderByType createDecoderByType()} to decode media. Each of these methods take a MIME type for the type of media you want to encode or decode, such as {@code "video/3gpp"} or {@code "audio/vorbis"}.

With an instance of {@link android.media.MediaCodec} created, you can then call {@link android.media.MediaCodec#configure configure()} to specify properties such as the media format or whether or not the content is encrypted.

Whether you're encoding or decoding your media, the rest of the process is the same after you create the {@link android.media.MediaCodec}. First call {@link android.media.MediaCodec#getInputBuffers()} to get an array of input {@link java.nio.ByteBuffer} objects and {@link android.media.MediaCodec#getOutputBuffers()} to get an array of output {@link java.nio.ByteBuffer} objects.

When you're ready to encode or decode, call {@link android.media.MediaCodec#dequeueInputBuffer dequeueInputBuffer()} to get the index position of the {@link java.nio.ByteBuffer} (from the array of input buffers) that you should use to to feed in your source media. After you fill the {@link java.nio.ByteBuffer} with your source media, release ownership of the buffer by calling {@link android.media.MediaCodec#queueInputBuffer queueInputBuffer()}.

Likewise for the output buffer, call {@link android.media.MediaCodec#dequeueOutputBuffer dequeueOutputBuffer()} to get the index position of the {@link java.nio.ByteBuffer} where you'll receive the results. After you read the output from the {@link java.nio.ByteBuffer}, release ownership by calling {@link android.media.MediaCodec#releaseOutputBuffer releaseOutputBuffer()}.

You can handle encrypted media data in the codecs by calling {@link android.media.MediaCodec#queueSecureInputBuffer queueSecureInputBuffer()} in conjunction with the {@link android.media.MediaCrypto} APIs, instead of the normal {@link android.media.MediaCodec#queueInputBuffer queueInputBuffer()}.

For more information about how to use codecs, see the {@link android.media.MediaCodec} documentation.

Record audio on cue

New method {@link android.media.AudioRecord#startRecording startRecording()} allows you to begin audio recording based on a cue defined by a {@link android.media.MediaSyncEvent}. The {@link android.media.MediaSyncEvent} specifies an audio session (such as one defined by {@link android.media.MediaPlayer}), which when complete, triggers the audio recorder to begin recording. For example, you can use this functionality to play an audio tone that indicates the beginning of a recording session and recording automatically begins so you don't have to manually synchronize the tone and the beginning of recording.

Timed text tracks

The {@link android.media.MediaPlayer} now handles both in-band and out-of-band text tracks. In-band text tracks come as a text track within an MP4 or 3GPP media source. Out-of-band text tracks can be added as an external text source via {@link android.media.MediaPlayer#addTimedTextSource addTimedTextSource()} method. After all external text track sources are added, {@link android.media.MediaPlayer#getTrackInfo()} should be called to get the refreshed list of all available tracks in a data source.

To set the track to use with the {@link android.media.MediaPlayer}, you must call {@link android.media.MediaPlayer#selectTrack selectTrack()}, using the index position for the track you want to use.

To be notified when the text track is ready to play, implement the {@link android.media.MediaPlayer.OnTimedTextListener} interface and pass it to {@link android.media.MediaPlayer#setOnTimedTextListener setOnTimedTextListener()}.

Audio effects

The {@link android.media.audiofx.AudioEffect} class now supports additional audio pre-processing types when capturing audio:

You can apply these pre-processor effects on audio captured with an {@link android.media.AudioRecord} using one of the {@link android.media.audiofx.AudioEffect} subclasses.

Note: It's not guaranteed that all devices support these effects, so you should always first check availability by calling {@link android.media.audiofx.AcousticEchoCanceler#isAvailable isAvailable()} on the corresponding audio effect class.

Gapless playback

You can now perform gapless playback between two separate {@link android.media.MediaPlayer} objects. At any time before your first {@link android.media.MediaPlayer} finishes, call {@link android.media.MediaPlayer#setNextMediaPlayer setNextMediaPlayer()} and Android attempts to start the second player the moment that the first one stops.

Media router. The new APIs MediaRouter, MediaRouteActionProvider, and MediaRouteButton provide standard mechanisms and UI for choosing where to play media.

Camera

Auto focus movement

The new interface {@link android.hardware.Camera.AutoFocusMoveCallback} allows you to listen for changes to the auto focus movement. You can register your interface with {@link android.hardware.Camera#setAutoFocusMoveCallback setAutoFocusMoveCallback()}. Then when the camera is in a continuous autofocus mode ({@link android.hardware.Camera.Parameters#FOCUS_MODE_CONTINUOUS_VIDEO} or {@link android.hardware.Camera.Parameters#FOCUS_MODE_CONTINUOUS_PICTURE}), you'll receive a call to {@link android.hardware.Camera.AutoFocusMoveCallback#onAutoFocusMoving onAutoFocusMoving()}, which tells you whether auto focus has started moving or has stopped moving.

Camera sounds

The {@link android.media.MediaActionSound} class provides a simple set of APIs to produce standard sounds made by the camera or other media actions. You should use these APIs to play the appropriate sound when building a custom still or video camera.

To play a sound, simply instantiate a {@link android.media.MediaActionSound} object, call {@link android.media.MediaActionSound#load load()} to pre-load the desired sound, then at the appropriate time, call {@link android.media.MediaActionSound#play play()}.

Connectivity

Android Beam

Android Beam™ now supports large payload transfers over Bluetooth. When you define the data to transfer with either the new {@link android.nfc.NfcAdapter#setBeamPushUris setBeamPushUris()} method or the new callback interface {@link android.nfc.NfcAdapter.CreateBeamUrisCallback}, Android hands off the data transfer to Bluetooth or another alternate transport to achieve faster transfer speeds. This is especially useful for large payloads such as image and audio files and requires no visible pairing between the devices. No additional work is required by your app to take advantage of transfers over Bluetooth.

The {@link android.nfc.NfcAdapter#setBeamPushUris setBeamPushUris()} method takes an array of {@link android.net.Uri} objects that specify the data you want to transfer from your app. Alternatively, you can implement the {@link android.nfc.NfcAdapter.CreateBeamUrisCallback} interface, which you can specify for your activity by calling {@link android.nfc.NfcAdapter#setBeamPushUrisCallback setBeamPushUrisCallback()}.

When using the callback interface, the system calls the interface's {@link android.nfc.NfcAdapter.CreateBeamUrisCallback#createBeamUris createBeamUris()} method when the user executes a share with Android Beam so that you can define the URIs to share at share-time. This is useful if the URIs to share might vary depending on the user context within the activity, whereas calling {@link android.nfc.NfcAdapter#setBeamPushUris setBeamPushUris()} is useful when the URIs to share are unchanging and you can safely define them ahead of time.

Network service discovery

Android 4.1 adds support for multicast DNS-based service discovery, which allows you to find and connect to services offered by peer devices over Wi-Fi, such as mobile devices, printers, cameras, media players, and others that are registered on the local network.

The new package {@link android.net.nsd} contains the new APIs that allow you to broadcast your services on the local network, discover local devices on the network, and connect to devices.

To register your service, you must first create an {@link android.net.nsd.NsdServiceInfo} object and define the various properties of your service with methods such as {@link android.net.nsd.NsdServiceInfo#setServiceName setServiceName()}, {@link android.net.nsd.NsdServiceInfo#setServiceType setServiceType()}, and {@link android.net.nsd.NsdServiceInfo#setPort setPort()}.

Then you need to implement {@link android.net.nsd.NsdManager.RegistrationListener} and pass it to {@link android.net.nsd.NsdManager#registerService registerService()} with your {@link android.net.nsd.NsdServiceInfo}.

To discover services on the network, implement {@link android.net.nsd.NsdManager.DiscoveryListener} and pass it to {@link android.net.nsd.NsdManager#discoverServices discoverServices()}.

When your {@link android.net.nsd.NsdManager.DiscoveryListener} receives callbacks about services found, you need to resolve the service by calling {@link android.net.nsd.NsdManager#resolveService resolveService()}, passing it an implementation of {@link android.net.nsd.NsdManager.ResolveListener} that receives an {@link android.net.nsd.NsdServiceInfo} object that contains information about the discovered service, allowing you to initiate the connection.

Wi-Fi Direct service discovery

The Wi-Fi Direct APIs are enhanced in Android 4.1 to support pre-association service discovery in the {@link android.net.wifi.p2p.WifiP2pManager}. This allows you to discover and filter nearby devices by services using Wi-Fi Direct before connecting to one, while Network Service Discovery allows you to discover a service on an existing connected network (such as a local Wi-Fi network).

To broadcast your app as a service over Wi-Fi so that other devices can discover your app and connect to it, call {@link android.net.wifi.p2p.WifiP2pManager#addLocalService addLocalService()} with a {@link android.net.wifi.p2p.nsd.WifiP2pServiceInfo} object that describes your app services.

To initiate discover of nearby devices over Wi-Fi, you need to first decide whether you'll communicate using Bonjour or Upnp. To use Bonjour, first set up some callback listeners with {@link android.net.wifi.p2p.WifiP2pManager#setDnsSdResponseListeners setDnsSdResponseListeners()}, which takes both a {@link android.net.wifi.p2p.WifiP2pManager.DnsSdServiceResponseListener} and {@link android.net.wifi.p2p.WifiP2pManager.DnsSdTxtRecordListener}. To use Upnp, call {@link android.net.wifi.p2p.WifiP2pManager#setUpnpServiceResponseListener setUpnpServiceResponseListener()}, which takes a {@link android.net.wifi.p2p.WifiP2pManager.UpnpServiceResponseListener}.

Before you can start discovering services on local devices, you also need to call {@link android.net.wifi.p2p.WifiP2pManager#addServiceRequest addServiceRequest()}. When the {@link android.net.wifi.p2p.WifiP2pManager.ActionListener} you pass to this method receives a successful callback, you can then begin discovering services on local devices by calling {@link android.net.wifi.p2p.WifiP2pManager#discoverServices discoverServices()}.

When local services are discovered, you'll receive a callback to either the {@link android.net.wifi.p2p.WifiP2pManager.DnsSdServiceResponseListener} or {@link android.net.wifi.p2p.WifiP2pManager.UpnpServiceResponseListener}, depending on whether you registered to use Bonjour or Upnp. The callback received in either case contains a {@link android.net.wifi.p2p.WifiP2pDevice} object representing the peer device.

Network usage

The new method {@link android.net.ConnectivityManager#isActiveNetworkMetered} allows you to check whether the device is currently connected to a metered network. By checking this state before performing intensive network transactions, you can help manage the data usage that may cost your users money and make informed decisions about whether to perform the transactions now or later (such as when the device becomes connected to Wi-Fi).

Accessibility

Accessibility service APIs

The reach of accessibility service APIs has been significantly increased in Android 4.1. It now allows you to build services that monitor and respond to more input events, such as complex gestures using {@link android.accessibilityservice.AccessibilityService#onGesture onGesture()} and other input events through additions to the {@link android.view.accessibility.AccessibilityEvent}, {@link android.view.accessibility.AccessibilityNodeInfo} and {@link android.view.accessibility.AccessibilityRecord} classes.

Accessibility services can also perform actions on behalf of the user, including clicking, scrolling and stepping through text using {@link android.view.accessibility.AccessibilityNodeInfo#performAction performAction} and {@link android.view.accessibility.AccessibilityNodeInfo#setMovementGranularities setMovementGranularities}. The {@link android.accessibilityservice.AccessibilityService#performGlobalAction performGlobalAction()} method also allows services to perform actions such as Back, Home, and open Recent Apps and Notifications.

Customizable app navigation

When building an Android app, you can now customize navigation schemes by finding focusable elements and input widgets using {@link android.view.accessibility.AccessibilityNodeInfo#findFocus findFocus()} and {@link android.view.accessibility.AccessibilityNodeInfo#focusSearch focusSearch()}, and set focus using {@link android.view.accessibility.AccessibilityNodeInfo#setAccessibilityFocused setAccessibilityFocused()}.

More accessible widgets

The new {@code android.view.accessibility.AccessibilityNodeProvider} class allows you to surface complex custom views to accessibility services so they can present the information in a more accessible way. The {@code android.view.accessibility.AccessibilityNodeProvider} allows a user widget with advanced content, such as a calendar grid, to present a logical semantic structure for accessibility services that is completely separate from the widget’s layout structure. This semantic structure allows accessibility services to present a more useful interaction model for users who are visually impaired.

Copy and Paste

Copy and paste with intents

You can now associate a {@link android.content.ClipData} object with an {@link android.content.Intent} using the {@link android.content.Intent#setClipData setClipData()} method. This is especially useful when using an intent to transfer multiple {@code content:} URIs to another application, such as when sharing multiple documents. The {@code content:} URIs supplied this way will also respect the intent's flags to offer read or write access, allowing you to grant access to multiple URIs in an the intent. When starting an {@link android.content.Intent#ACTION_SEND} or {@link android.content.Intent#ACTION_SEND_MULTIPLE} intent, the URIs supplied in the intent are now automatically propagated to the {@link android.content.ClipData} so that the receiver can have access granted to them.

Support for HTML and string styles

The {@link android.content.ClipData} class now supports styled text (either as HTML or Android styled strings). You can add HTML styled text to the {@link android.content.ClipData} with {@link android.content.ClipData#newHtmlText newHtmlText()}.

Renderscript

Renderscript computation functionality has been enhanced with the following features:

New pragmas are also available to define the floating point precision required by your compute Renderscripts. This lets you enable NEON like operations such as fast vector math operations on the CPU path that wouldn’t otherwise be possible with full IEEE 754-2008 standard.

Note: The experimental Renderscript graphics engine is now deprecated.

Animation

Activity launch animations

You can now launch an {@link android.app.Activity} using zoom animations or your own custom animations. To specify the animation you want, use the {@link android.app.ActivityOptions} APIs to build a {@link android.os.Bundle} that you can then pass to any of the methods that start an activity, such as {@link android.app.Activity#startActivity(Intent,Bundle) startActivity()}.

The {@link android.app.ActivityOptions} class includes a different method for each type of animation you may want to show as your activity opens:

{@link android.app.ActivityOptions#makeScaleUpAnimation makeScaleUpAnimation()}
Creates an animation that scales up the activity window from a specified starting position on the screen and a specified starting size. For example, the home screen in Android 4.1 uses this when opening an app.
{@link android.app.ActivityOptions#makeThumbnailScaleUpAnimation makeThumbnailScaleUpAnimation()}
Creates an animation that scales up the activity window starting from a specified position and a provided thumbnail image. For example, the Recent Apps window in Android 4.1 uses this when returning to an app.
{@link android.app.ActivityOptions#makeCustomAnimation makeCustomAnimation()}
Creates an animation defined by your own resources: one that defines the animation for the activity opening and another for the activity being stopped.

Time animator

The new {@link android.animation.TimeAnimator} provides a simple callback mechanism with the {@link android.animation.TimeAnimator.TimeListener} that notifies you upon every frame of the animation. There is no duration, interpolation, or object value-setting with this Animator. The listener's callback receives information for each frame including total elapsed time and the elapsed time since the previous animation frame.

User Interface

Notifications

In Android 4.1, you can create notifications with larger content regions, big image previews, multiple action buttons, and configurable priority.

Notification styles

The new method {@link android.app.Notification.Builder#setStyle setStyle()} allows you to specify one of three new styles for your notification that each offer a larger content region. To specify the style for your large content region, pass {@link android.app.Notification.Builder#setStyle setStyle()} one of the following objects:

{@link android.app.Notification.BigPictureStyle}
For notifications that includes a large image attachment.
{@link android.app.Notification.BigTextStyle}
For notifications that includes a lot of text, such as a single email.
{@link android.app.Notification.InboxStyle}
For notifications that include a list of strings, such as snippets from multiple emails.
Notification actions

There's now support for up to two action buttons that appear at the bottom of the notification message, whether your notification uses the normal or larger style.

To add an action button, call {@link android.app.Notification.Builder#addAction addAction()}. This method takes three arguments: a drawable resource for an icon, text for the button, and a {@link android.app.PendingIntent} that defines the action to perfrom.

Priorities

You can now hint to the system how important your notification is to affect the order of your notification in the list by setting the priority with {@link android.app.Notification.Builder#setPriority setPriority()}. You can pass this one of five different priority levels defined by {@code PRIORITY_*} constants in the {@link android.app.Notification} class. The default is {@link android.app.Notification#PRIORITY_DEFAULT}, and there's two levels higher and two levels lower.

High priority notifications are things that users generally want to respond to quickly, such as a new instant message, text message, or impending event reminder. Low priority notifications are things like expired calendar events or app promotions.

Controls for system UI

Android 4.0 (Ice Cream Sandwich) added new flags to control the visibility of the system UI elements, such as to dim the appearance of the system bar or make it disappear completely on handsets. Android 4.1 adds a few more flags that allow you to further control the appearance of system UI elements and your activity layout in relation to them by calling {@link android.view.View#setSystemUiVisibility setSystemUiVisibility()} and passing the following flags:

{@link android.view.View#SYSTEM_UI_FLAG_FULLSCREEN}
Hides non-critical system UI (such as the status bar). If your activity uses the action bar in overlay mode (by enabling {@code android:windowActionBarOverlay}), then this flag also hides the action bar and does so with a coordinated animation when both hiding and showing the two.
{@link android.view.View#SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN}
Sets your activity layout to use the same screen area that's available when you've enabled {@link android.view.View#SYSTEM_UI_FLAG_FULLSCREEN} even if the system UI elements are still visible. Although parts of your layout will be overlayed by the system UI, this is useful if your app often hides and shows the system UI with {@link android.view.View#SYSTEM_UI_FLAG_FULLSCREEN}, because it avoids your layout from adjusting to the new layout bounds each time the system UI hides or appears.
{@link android.view.View#SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION}
Sets your activity layout to use the same screen area that's available when you've enabled {@link android.view.View#SYSTEM_UI_FLAG_HIDE_NAVIGATION} (added in Android 4.0) even if the system UI elements are still visible. Although parts of your layout will be overlayed by the navigation bar, this is useful if your app often hides and shows the navigation bar with {@link android.view.View#SYSTEM_UI_FLAG_HIDE_NAVIGATION}, because it avoids your layout from adjusting to the new layout bounds each time the navigation bar hides or appears.
{@link android.view.View#SYSTEM_UI_FLAG_LAYOUT_STABLE}
You might want to add this flag if you're using {@link android.view.View#SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN} and/or {@link android.view.View#SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION} to ensure that when you call {@link android.view.View#fitSystemWindows fitSystemWindows()} on a view that the bounds defined remain consistent with regard to the available screen space. That is, with this flag set, {@link android.view.View#fitSystemWindows fitSystemWindows()} will behave as if the visibility of system UI elements is unchanged even after you hide all system UI.

For more discussion about the other related system UI flags, read about those added in Android 4.0.

Remote views

{@link android.widget.GridLayout} and {@link android.view.ViewStub} are now remotable views so you can use them in layouts for your app widgets and notification custom layouts.

Font families

Android 4.1 adds several more variants of the Roboto font style for a total of 10 variants, and they're all usable by apps. Your apps now have access to the full set of both light and condensed variants.

The complete set of Roboto font variants available is:

You can apply any one of these with the new {@link android.R.attr#fontFamily} attribute in combination with the {@link android.R.attr#textStyle} attribute.

Supported values for {@link android.R.attr#fontFamily} are:

You can then apply bold and/or italic with {@link android.R.attr#textStyle} values {@code "bold"} and {@code "italic"}. You can apply both like so: {@code android:textStyle="bold|italic"}.

You can also use {@link android.graphics.Typeface#create Typeface.create()}. For example, {@code Typeface.create("sans-serif-light", Typeface.NORMAL)}.

Input Framework

Multiple input devices

The new {@link android.hardware.input.InputManager} class allows you to query the set of input devices current connected and register to be notified when a new device is added, changed, or removed. This is particularly useful if you're building a game that supports multiple players and you want to detect how many controllers are connected and when there are changes to the number of controllers.

You can query all input devices connected by calling {@link android.hardware.input.InputManager#getInputDeviceIds()}. This returns an array of integers, each of which is an ID for a different input device. You can then call {@link android.hardware.input.InputManager#getInputDevice getInputDevice()} to acquire an {@link android.view.InputDevice} for a specified input device ID.

If you want to be informed when new input devices are connected, changed, or disconnected, implement the {@link android.hardware.input.InputManager.InputDeviceListener} interface and register it with {@link android.hardware.input.InputManager#registerInputDeviceListener registerInputDeviceListener()}.

Vibrate for input controllers

If connected input devices have their own vibrate capabilities, you can now control the vibration of those devices using the existing {@link android.os.Vibrator} APIs simply by calling {@link android.view.InputDevice#getVibrator()} on the {@link android.view.InputDevice}.

Permissions

The following are new permissions:

{@link android.Manifest.permission#READ_EXTERNAL_STORAGE}
Provides protected read access to external storage. In Android 4.1 by default all applications still have read access. This will be changed in a future release to require that applications explicitly request read access using this permission. If your application already requests write access, it will automatically get read access as well. There is a new developer option to turn on read access restriction, for developers to test their applications against how Android will behave in the future.
{@link android.Manifest.permission#READ_USER_DICTIONARY}
Allows an application to read the user dictionary. This should only be required by an IME, or a dictionary editor like the Settings app.
{@link android.Manifest.permission#READ_CALL_LOG}
Allows an application to read the system's call log that contains information about incoming and outgoing calls.
{@link android.Manifest.permission#WRITE_CALL_LOG}
Allows an application to modify the system's call log stored on your phone
{@link android.Manifest.permission#WRITE_USER_DICTIONARY}
Allows an application to write to the user's word dictionary.

Device Features

Android 4.1 includes a new feature declaration for devices that are dedicated to displaying the user interface on a television screen: {@link android.content.pm.PackageManager#FEATURE_TELEVISION}. To declare that your app requires a television interface, declare this feature in your manifest file with the {@code <uses-feature>} element:

<manifest ... >
    <uses-feature android:name="android.hardware.type.television"
                  android:required="true" />
    ...
</manifest>

This feature defines "television" to be a typical living room television experience: displayed on a big screen, where the user is sitting far away and the dominant form of input is be something like a d-pad, and generally not through touch or a mouse/pointer-device.