docs/html/preview/api-overview.jd

page.title=Android N for Developers
meta.tags="preview", "androidn"
page.tags="preview", "developer preview"
page.image=images/cards/card-n-apis_2x.png
@jd:body




<div id="qv-wrapper">
<div id="qv">
  <h2>Key developer features</h2>
  <ol>
      <ul style="list-style-type:none;">
        <li><a href="#multi-window_support">Multi-window support</a></li>
        <li><a href="#notification_enhancements">Notifications</a></li>
        <li><a href="#jit_aot">JIT/AOT compilation</a></li>
        <li><a href="#quick_path_to_app_install">Quick path to app install</a></li>
        <li><a href="#doze_on_the_go">Doze on the go</a></li>
        <li><a href="#background_optimizations">Background optimizations</a></li>
        <li><a href="#data_saver">Data Saver</a></li>
        <li><a href="#vulkan">Vulkan API</a></li>
        <li><a href="#tile_api">Quick Settings Tile API</a></li>
        <li><a href="#number-blocking">Number-blocking</a></li>
        <li><a href="#call_screening">Call screening</a></li>
        <li><a href="#multi-locale_languages">Locales and languages</a></li>
        <li><a href="#emoji">New Emojis</a></li>
        <li><a href="#icu4">ICU4J APIs in Android</a></li>
        <li><a href="#gles_32">OpenGL ES 3.2 API</a></li>
        <li><a href="#android_tv_recording">Android TV recording</a></li>
        <li><a href="#android_for_work">Android for Work</a></li>
        <li><a href="#accessibility_enhancements">Accessibility</a></li>
        <li><a href="#direct_boot">Direct Boot</a></li>
        <li><a href="#key_attestation">Key Attestation</a></li>
        <li><a href="#network_security_config">Network Security Config</a></li>
        <li><a href="#default_trusted_ca">Default Trusted CA</a></li>
        <li><a href="#apk_signature_v2">APK signature scheme v2</a></li>
        <li><a href="#scoped_directory_access">Scoped directory access</a></li>
        <li><a href="#print_svc">Print service enhancements</a></li>
        <li><a href="#virtual_files">Virtual Files</a></li>
      </ol>
</div>
</div>



<p>Android N is still in active development, but you can try it
now as part of the N Developer Preview. The sections below highlight some of
the new features for developers. </p>

<p>
  Make sure to check out the <a href=
  "{@docRoot}preview/behavior-changes.html">Behavior Changes</a> to learn about
  areas where platform changes may affect your apps, take a look at the
  developer guides to learn more about key features, and download the <a href=
  "{@docRoot}preview/setup-sdk.html#docs-dl">API Reference</a> for details on
  new APIs.
</p>

<h2 id="multi-window_support">Multi-window support</h2>


<p>In Android N, we're introducing a new and much-requested multitasking feature
into the platform &mdash; multi-window support. </p>

  <p>Users can now pop open two apps on the screen at once. </p>
  <ul>
  <li>On phones and tablets
running Android N, users can run two apps side-by-side or
one-above-the-other in splitscreen mode. Users can resize the apps by dragging
the divider between them. </li>

<li>On Android TV devices, apps can put themselves in <a
href="{@docRoot}preview/features/picture-in-picture.html">picture-in-picture
mode</a>, allowing them to continue showing content while the user browses or
interacts with other apps.</li>
  </ul>

<div class="col-4of10">
<img src="{@docRoot}preview/images/mw-portrait.png" alt="" style="height:460px;padding-left:1em;"
    id="img-split-screen" />
<p class="img-caption">
  <strong>Figure 1.</strong> Apps running in split-screen mode.
</p>
  </div>

<p>Especially on tablets and other larger-screen devices, multi-window support
gives you new ways to engage users. You can even enable drag-and-drop in
your app to let users conveniently drag content to or from your app &mdash; a great
way to enhance your user experience. </p>

<p>It's straightforward to add multi-window support to your app and configure how it
handles multi-window display. For example, you can specify your activity's
minimum allowable dimensions, preventing users from resizing the activity below
that size. You can also disable multi-window display for your app, which
  ensures that the system will only show your app in full-screen mode.</p>

<p>
  For more information, see the <a href=
  "{@docRoot}preview/features/multi-window.html">Multi-Window Support</a>
  developer documentation.
</p>

<h2 id="notification_enhancements">Notification enhancements</h2>

<p>In Android N we've redesigned notifications to make them easier and faster to
use. Some of the changes include:</p>

<ul>
  <li>
    <strong>Template updates</strong>: We're updating notification templates to
    put a new emphasis on hero image and avatar. Developers will be able to
    take advantage of the new templates with minimal adjustments in their code.
  </li>

  <li>
    <strong>Message style customization</strong>: You can customize more of the
    user interface labels associated with your notifications using the
    <code>MessageStyle</code> class. You can configure the message, conversation
    title, and content view.
  </li>

  <li>
    <strong>Bundled notifications</strong>: The system can group messages
    together, for example by message topic, and display the group. A user can
    take actions, such as Dismiss or Archive, on them in place. If you’ve
    implemented notifications for Android Wear, you’ll already be familiar with
    this model.
  </li>

  <li>
    <strong>Direct reply</strong>: For real-time communication apps, the
    Android system supports inline replies so that users can quickly respond to
    an SMS or text message directly within the notification interface.
  </li>

  <li>
    <strong>Custom views</strong>: Two new APIs enable you to leverage system
    decorations, such as notification headers and actions, when using custom
    views in notifications.
  </li>
</ul>

<div class="col-4of12">
  <img src="{@docRoot}preview/images/notifications-1.png" alt=""
  style="padding:.5em;max-width:226px">
</div>

<div class="col-4of12">
  <img src="{@docRoot}preview/images/notifications-3.png" alt=""
  style="padding:.5em;max-width:226px">
</div>

<div class="col-4of12">
  <img src="{@docRoot}preview/images/notifications-2.png" alt=""
  style="padding:.5em;max-width:226px">
</div>


<p class="img-caption">
  <strong>Figure 2.</strong> Bundled notifications and direct reply.
</p>

<p>To learn how to implement the new features, see the
  <a href="{@docRoot}preview/features/notification-updates.html">Notifications</a>
  guide.</p>



<h2 id="jit_aot">Profile-guided JIT/AOT compilation</h2>

<p>In Android N, we've added a Just in Time (JIT) compiler with code profiling to
ART, which lets it constantly improve the performance of Android apps as they
run. The JIT compiler complements ART's current Ahead of Time (AOT) compiler
and helps improve runtime performance, save storage space, and speed up app
updates and system updates.</p>

<p>Profile-guided compilation lets ART manage the AOT/JIT compilation for each app
according to its actual usage, as well as conditions on the device. For
example, ART maintains a profile of each app's hot methods and can precompile
and cache those methods for best performance. It leaves other parts of the app
uncompiled until they are actually used.</p>

<p>Besides improving performance for key parts of the app, profile-guided
compilation helps reduce an app's overall RAM footprint, including associated
binaries. This feature is especially important on low-memory devices.</p>

<p>ART manages profile-guided compilation in a way that minimizes impact on the
device battery. It does precompilation only when then the device is idle and
charging, saving time and battery by doing that work in advance.</p>

<h2 id="quick_path_to_app_install">Quick path to app install</h2>

<p>One of the most tangible benefits of ART's JIT compiler is the speed of app
installs and system updates. Even large apps that required several minutes to
optimize and install in Android 6.0 can now install in just a matter of
seconds. System updates are also faster, since there's no more optimizing step. </p>

<h2 id="doze_on_the_go">Doze on the go...</h2>

<p>Android 6.0 introduced Doze, a system mode that saves battery by deferring
apps' CPU and network activities when the device is idle, such as when it's
sitting on a table or in a drawer. </p>

<p>Now in Android N, Doze takes a step further and saves battery while on the go.
Any time the screen is off for a period of time and the device is unplugged,
Doze applies a subset of the familiar CPU and network restrictions to apps.
This means users can save battery even when carrying their devices in their
pockets.</p>


<img src="/preview/images/doze-diagram-1.png"
  alt="" id="figure1" />
<p class="img-caption">
  <strong>Figure 3.</strong> Doze now applies
  restrictions to improve battery life even when the device is not stationary.
</p>


<p>A short time after the screen turns off while the device is on battery, Doze
restricts network access and defers jobs and syncs. During brief maintenance
windows, applications are allowed network access and any of their deferred
jobs/syncs are executed. Turning the screen on or plugging in the device brings
the device out of Doze.</p>

<p>When the device is stationary again, with screen off and on battery for a
period of time, Doze applies the full CPU and network restrictions on {@link
android.os.PowerManager.WakeLock}, {@link android.app.AlarmManager} alarms, and
GPS/Wi-Fi scans.</p>

<p>The best practices for adapting your app to Doze are the same whether the
device is moving or not, so if you already updated your app to gracefully
handle Doze, you're all set. If not, start <a
href="{@docRoot}training/monitoring-device-state/doze-standby.html#assessing_your_app">adapting
your app to Doze</a> now.</p>

<h2 id="background_optimizations">Project Svelte: Background optimizations</h2>

<p>Project Svelte is an ongoing effort to minimize RAM use by system and apps
across the range of Android devices in the ecosystem. In Android N, Project
Svelte is focused on optimizing the way apps run in the background. </p>

<p>Background processing is an essential part of most apps. When handled right, it
can make your user experience amazing &mdash; immediate, fast, and context-aware.
When not handled right, background processing can needlessly consume RAM (and
battery) and affect system performance for other apps. </p>

<p>Since Android 5.0, {@link android.app.job.JobScheduler} has been the
preferred way of performing background work in a way that's good
for users. Apps can schedule jobs while letting the system optimize based on
memory, power, and connectivity conditions. JobScheduler offers control and
simplicity, and we want all apps to use it. </p>

<p>
  Another good option is <a href=
  "https://developers.google.com/android/reference/com/google/android/gms/gcm/GcmNetworkManager">
  <code>GCMNetworkManager</code></a>, part of Google Play Services, which
  offers similar job scheduling with compatibility across legacy versions of
  Android.
</p>

<p>We're continuing to extend <code>JobScheduler</code> and
<code>GCMNetworkManager</code> to meet more of
your use cases &mdash; for example, in Android N you can now schedule background
work based on changes in Content Providers. At the same time we're starting to
deprecate some of the older patterns that can reduce system performance,
especially on low-memory devices.</p>

<p>In Android N we're removing three commonly-used implicit broadcasts &mdash;
 {@link android.net.ConnectivityManager#CONNECTIVITY_ACTION}, {@link
  android.hardware.Camera#ACTION_NEW_PICTURE}, and {@link
  android.hardware.Camera#ACTION_NEW_VIDEO} &mdash; since those can wake the
background processes of multiple apps at once and strain memory and battery. If
your app is receiving these, take advantage of the N Developer Preview to
  migrate to <code>JobScheduler</code> and related APIs instead. </p>

<p>
  Take a look at the <a href=
  "{@docRoot}preview/features/background-optimization.html">Background
  Optimizations</a> documentation for details.
</p>


<h2 id="data_saver">Data Saver</h2>

<div class="col-5of12" style="margin-right:1.5em;">
<img src="{@docRoot}preview/images/datasaver.png" style="border:2px solid #ddd">

<p class="img-caption" style="padding-right:2em;">
  <strong>Figure 4.</strong> Data Saver in Settings.
</p>
  </div>

<p>Over the life of a mobile device, the cost of a cellular data plan typically
exceeds the cost of the device itself. For many users, cellular data is an
expensive resource that they want to conserve. </p>

<p>Android N introduces Data Saver mode, a new system service that helps reduce
cellular data use by apps, whether roaming, near the end of the billing cycle,
or on a small prepaid data pack. Data Saver gives users control over how apps
use cellular data and lets developers provide more efficient service when Data
Saver is on. </p>

<p>When a user enables Data Saver in <strong>Settings</strong> and the device is
on a metered network, the system blocks background data usage and signals apps
to use less data in the foreground wherever possible &mdash; such as by limiting
bit rate for streaming, reducing image quality, deferring optimistic precaching,
and so on. Users can whitelist specific apps to allow background metered data
usage even when Data Saver is turned on.</p>

<p>Android N extends the {@link android.net.ConnectivityManager} to provide apps a
way to <a href="{@docRoot}preview/features/data-saver.html#status">retrieve the
user's Data Saver preferences</a> and <a
href="{@docRoot}preview/features/data-saver.html#monitor-changes">monitor
preference changes</a>. All apps should check whether the user has enabled Data
Saver and make an effort to limit foreground and background data usage.</p>


<h2 id="vulkan">Vulkan API</h2>

<p>
  Android N integrates <a href="http://www.khronos.org/vulkan" class=
  "external-link">Vulkan™</a>, a new 3D rendering API, into the platform. Like
  <a href="https://www.khronos.org/opengles/" class="external-link">OpenGL™
  ES</a>, Vulkan is an open standard for 3D graphics and rendering maintained
  by the Khronos Group.
</p>

<p>
  Vulkan is designed from the ground up to minimize CPU overhead in the driver,
  and allow your application to control GPU operation more directly. Vulkan
  also enables better parallelization by allowing multiple threads to perform
  work such as command buffer construction at once.
</p>

<p>
  Vulkan development tools and libraries are rolled into the Android NDK. They
  include:
</p>

<ul>
  <li>Headers
  </li>

  <li>Validation layers (debug libraries)
  </li>

  <li>SPIR-V shader compiler
  </li>

  <li>SPIR-V runtime shader compilation library
  </li>
</ul>

<p>
  Vulkan is only available to apps on devices with Vulkan-capable hardware,
  such as Nexus 5X and Nexus 6P. We're working closely with our
  partners to bring Vulkan to more devices as soon as possible.
</p>

<p>
  For more information, see the the <a href=
  "{@docRoot}ndk/guides/graphics/index.html">API documentation</a>.
</p>

<h2 id="tile_api">Quick Settings Tile API</h2>


<div style="float:right;max-width:320px">
<img src="{@docRoot}preview/images/quicksettings.png" style="padding-left:1.5em;">

<p class="img-caption" style="padding-left:2em;">
  <strong>Figure 5.</strong> Quick Settings tiles in the notification shade.
</p>


  </div><p>Quick Settings is a popular and simple way to expose key settings and actions,
directly from the notification shade. In Android N, we've expanded the scope of
Quick Settings to make it even more useful and convenient. </p>

<p>We've added more room for additional Quick Settings tiles, which users can
access across a paginated display area by swiping left or right. We've also
given users control over what Quick Settings tiles appear and where they are
displayed &mdash; users can add or move tiles just by dragging and dropping them. </p>

<p>For developers, Android N also adds a new API that lets you define your own
  Quick Settings tiles to give users easy access to key controls and actions in your app.</p>

<p>
  Quick Settings tiles are reserved for controls or actions that are either
  urgently required or frequently used, and should not be used as shortcuts to
  launching an app.
</p>

<p>
  Once you’ve defined your tiles, you can surface them to users, who can add
  them to Quick Settings just by drag and drop.
</p>

<p>
  For information about creating an app tile, see the
  <code>android.service.quicksettings.Tile</code> in the downloadable <a href=
  "{@docRoot}preview/setup-sdk.html#docs-dl">API Reference</a>.
</p>



<h2 id="number-blocking">Number-blocking</h2>

<p>Android N now supports number-blocking in the platform and provides a
framework API to let service providers maintain a blocked-number list. The
default SMS app, the default phone app, and carrier apps can read from and
write to the blocked-number list. The list is not accessible to other apps.</p>

<p>By making number-blocking a standard feature of the platform, Android provides
a consistent way for apps to support number-blocking across a wide range of
devices. Among the other benefits that apps can take advantage of are:</p>

<ul>
  <li> Numbers blocked on calls are also blocked on texts
  <li> Blocked numbers can persist across resets and devices through the Backup &amp;
Restore feature
  <li> Multiple apps can use the same blocked numbers list
</ul>

<p>Additionally, carrier app integration through Android means that carriers can
read the blocked numbers list on the device and perform service-side blocking
for the user in order to stop unwanted calls and texts from reaching the user
through any medium, such as a VOIP endpoint or forwarding phones.</p>

<p>
  For more information, see <code>android.provider.BlockedNumberContract</code>
  in the downloadable <a href="{@docRoot}preview/setup-sdk.html#docs-dl">API
  Reference</a>.
</p>

<h2 id="call_screening">Call screening</h2>

<p>
  Android N allows the default phone app to screen incoming calls. The phone
  app does this by implementing the new <code>CallScreeningService</code>,
  which allows the phone app to perform a number of actions based on an
  incoming call's {@link android.telecom.Call.Details Call.Details}, such as:
</p>

<ul>
  <li> Reject the incoming call
  <li> Do not allow the call to the call log
  <li> Do not show the user a notification for the call
</ul>

<p>
  For more information, see <code>android.telecom.CallScreeningService</code>
  in the downloadable <a href="{@docRoot}preview/setup-sdk.html#docs-dl">API
  Reference</a>.
</p>


<h2 id="multi-locale_languages">Multi-locale support, more languages</h2>


<p>Android N now lets users select <strong>multiple locales</strong> in Settings,
to better support bilingual use-cases. Apps can use
a new API to get the user's selected locales and then offer more sophisticated
user experiences for multi-locale users &mdash; such as showing search results in
multiple languages and not offering to translate webpages in a language the
user already knows.</p>

<p>Along with multi-locale support, Android N also expands the range of languages
available to users. It offers more than 25 variants each for commonly used
languages such as English, Spanish, French, and Arabic. It also adds partial
support for more than 100 new languages.</p>

<p>Apps can get the list of locales set by the user by calling <code>LocaleList.GetDefault()</code>.  To support the expanded number of locales, Android N is changing the way
that it resolves resources. Make sure that you test and verify that your apps
working as expected with the new resource resolution logic.</p>

<p>To learn about the new resource-resolution behavior and the best practices you
should follow, see <a href="{@docRoot}preview/features/multilingual-support.html"
>Multilingual Support</a>.</p>


<h2 id="emoji">New Emojis</h2>

<p>
  Android N introduces additional emojis and emoji-related features including
  skin tone emojis and support for variation
  selectors. If your app supports emojis,
  follow the guidelines below to take advantage of these emoji-related features.
</p>

<ul>
  <li>
    <strong>Check that a device contains an emoji before inserting it.</strong>
    To check which emojis are present in the
    system font, use the {@link android.graphics.Paint#hasGlyph(String)} method.
  </li>
  <li>
    <strong>Check that an emoji supports variation selectors.</strong>
    Variation selectors allow you to
    present certain emojis in color or in black-and-white.
    On mobile devices, apps should represent emojis in color rather than black-and-white. However,
    if your app displays emojis inline with text, then it should use the black-and-white variation.
    To determine whether an emoji has a variation, use the variation selector.
    For a complete list of characters with variations, review the
    <em>emoji variation sequences</em> section of the
    <a class="external-link"
    href="http://www.unicode.org/Public/9.0.0/ucd/StandardizedVariants-9.0.0d1.txt">
      Unicode documentation on variations</a>.
  </li>
  <li>
    <strong>Check that an emoji supports skin tone.</strong> Android N allows users to modify the
    rendered skin tone of emojis to their preference. Keyboard apps should provide visual
    indications for emojis that have multiple skin tones and should allow users to
    select the skin tone that they prefer. To determine which system emojis have
    skin tone modifiers, use the {@link android.graphics.Paint#hasGlyph(String)}
    method. You can determine which emojis use skin tones by reading the
    <a class="external-link"
    href="http://unicode.org/emoji/charts/full-emoji-list.html">
     Unicode documentation</a>.
  </li>
</ul>


<h2 id="icu4">ICU4J APIs in Android</h2>

<p>
  Android N now offers a subset of <a href=
  "http://site.icu-project.org/">ICU4J</a> APIs in the Android framework under
  the <code>android.icu</code> package. Migration is easy, and mostly entails
  simply changing from the <code>com.java.icu</code> namespace to
  <code>android.icu</code>. If you are already using an ICU4J bundle in your
  apps, switching to the <code>android.icu</code> APIs provided in the Android
  framework can produce substantial savings in APK size.
</p>

<p>
  To learn more about the Android ICU4J APIs, see <a href=
  "{@docRoot}preview/features/icu4j-framework.html">ICU4J Support</a>.
</p>



<h2 id="gles_32">OpenGL&trade; ES 3.2 API</h2>

<p>Android N adds framework interfaces and platform support for OpenGL ES 3.2, including:</p>

<ul>
  <li> All extensions from the <a class="external-link"
href="https://www.khronos.org/registry/gles/extensions/ANDROID/ANDROID_extension_pack_es31a.txt">Android Extension Pack</a></a> (AEP) except for <code>EXT_texture_sRGB_decode</code>.
  <li> Floating-point framebuffers for HDR and deferred shading.
  <li> BaseVertex draw calls to enable better batching and streaming.
  <li> Robust buffer access control to reduce WebGL overhead.
</ul>

<p>The framework API for OpenGL ES 3.2 on Android N is provided with the
<code>GLES32</code> class. When using OpenGL ES 3.2, be sure to declare the
requirement in your manifest file, using the <code>&lt;uses-feature&gt;</code> tag and
the <code>android:glEsVersion</code> attribute. </p>

<p>For information about using OpenGL ES, including how to check a device's
supported OpenGL ES version at runtime, see the <a
href="{@docRoot}guide/topics/graphics/opengl.html">OpenGL ES API guide</a>.</p>


<h2 id="android_tv_recording">Android TV recording</h2>

<p>Android N adds the ability to record and playback content from Android TV input
services via new recording APIs.  Building on top of existing time-shifting
APIs, TV input services can control what channel data can be recorded, how
recorded sessions are saved, and manage user interaction with recorded content. </p>

<p>For more information, see <a
href="{@docRoot}preview/features/tv-recording-api.html">Android TV Recording APIs</a>.</p>


<h2 id="android_for_work">Android for Work</h2>

<p>Android for Work adds many new features and APIs for devices running Android N.
Some highlights are below &mdash; for a complete list of changes, see
<a href="{@docRoot}preview/features/afw.html">Android for Work Updates</a>.</p>

<h3 id="work_profile_security_challenge">Work profile security challenge </h3>

<p>
  Profile owners targeting the N SDK
  can specify a separate security challenge for apps running in
  the work profile. The work challenge is shown when a user attempts to open
  any work apps. Successful completion of the security challenge unlocks the
  work profile and decrypts it if necessary. For profile owners,
  <code>ACTION_SET_NEW_PASSWORD</code> prompts the user to set a work
  challenge, and <code>ACTION_SET_NEW_PARENT_PROFILE_PASSWORD</code> prompts
  the user to set a device lock.
</p>

<p>
  Profile owners can set distinct passcode policies for the work challenge
  (such as how long the PIN needs to be, or whether a fingerprint can be used
  to unlock the profile) using the <code>setPasswordQuality()</code>,
  <code>setPasswordMinimumLength()</code> and related methods. The profile
  owner can also set the device lock using the <code>DevicePolicyManager</code>
  instance returned by the new <code>getParentProfileInstance()</code> method.
  Additionally, profile owners can customize the credentials screen for the
  work challenge using the new <code>setOrganizationColor()</code> and
  <code>setOrganizationName()</code> methods.
</p>
<h3 id="turn_off_work">Turn off work </h3>

<p>On a device with a work profile, users can toggle work mode. When work mode is
off the managed user is temporarily shut down, which disables work profile
apps, background sync, and notifications. This includes the profile owner
application. When work mode is off, the system displays a persistent status
icon to remind the user that they can't launch work apps. The launcher
indicates that work apps and widgets are not accessible. </p>

<h3 id="always_on_vpn">Always on VPN </h3>

<p>Device owners and profile owners can ensure that work apps always connect
through a specified VPN. The system automatically starts that VPN after the
device boots.</p>

<p>
  New <code>DevicePolicyManager</code> methods are
  <code>setAlwaysOnVpnPackage()</code> and
  <code>getAlwaysOnVpnPackage()</code>.
</p>

<p>Because VPN services can be bound directly by the system without app
interaction, VPN clients need to handle new entry points for Always on VPN. As
before, services are indicated to the system by an intent filter matching
action <code>android.net.VpnService</code>. </p>

<p>
  Users can also manually set Always on VPN clients that implement
  <code>VPNService</code> methods in the primary user using
  <strong>Settings&gt;More&gt;Vpn</strong>.
</p>

<h3 id="custom_provisioning">Customized provisioning</h3>

<p>
  An application can customize the profile owner and device owner provisioning
  flows with corporate colors and logos.
  <code>DevicePolicyManager.EXTRA_PROVISIONING_MAIN_COLOR</code> customizes
  flow color. <code>DevicePolicyManager.EXTRA_PROVISIONING_LOGO_URI</code>
  customizes the flow with a corporate logo.
</p>

<h2 id="accessibility_enhancements">Accessibility enhancements</h2>

<p>Android N now offers Vision Settings directly on the Welcome screen for new
device setup. This makes it much easier for users to discover and configure
accessibility features on their devices, including magnification gesture, font
size, display size, and TalkBack. </p>

<p>With these accessibility features getting more prominent placement, your users
are more likely to try your app with them enabled. Make sure you test your apps
early with these settings enabled. You can enable them from Settings >
Accessibility.</p>

<p>Also in Android N, accessibility services can now help users with motor
impairments to touch the screen. The new API allows building services with
features such as face-tracking, eye-tracking, point scanning, and so on, to
meet the needs of those users.</p>

<p>For more information, see <code>android.accessibilityservice.GestureDescription</code>
  in the downloadable <a href="{@docRoot}preview/setup-sdk.html#docs-dl">API Reference</a>.</p>


<h2 id="direct_boot">Direct boot</h2>

<p>Direct boot improves device startup times and lets registered
apps have limited functionality even after an unexpected reboot.
For example, if an encrypted device reboots while the user is sleeping,
registered alarms, messages and incoming calls can now continue notify
the user as normal. This also means accessibility services can also be
  available immediately after a restart.</p>

<p>Direct boot takes advantage of file based encryption in Android N
to enable fine grained encryption policies for both system and app data.
The system uses a device-encrypted store for select system data and explicitly
registered app data. By default a credential-encrypted store is used for all
  other system data, user data, apps, and app data. </p>

<p>At boot, the system starts in a restricted mode with access to
device-encrypted data only, and without general access to apps or data.
If you have components that you want to run in this mode, you can register
them by setting a flag in the manifest. After restart, the system activates
registered components by broadcasting the <code>LOCKED_BOOT_COMPLETED</code>
intent. The system ensures registered device-encrypted app data is available
before unlock. All other data is unavailable until the User confirms their lock
  screen credentials to decrypt it. </p>

For more information, see <a href="{@docRoot}preview/features/direct-boot.html">Direct Boot</a>.</p>
</p>


<h2 id="key_attestation">Key Attestation</h2>

<p>Hardware-backed keystores provide a much safer method to create, store,
and use cryptographic keys on Android devices. They protect keys from the
Linux kernel, potential Android vulnerabilities, and extraction
from rooted devices.</p>

<p>To make it easier and more secure to use hardware-backed keystores,
Android N introduces Key Attestation. Apps and off-devices can use Key
Attestation to strongly determine whether an RSA or EC key pair is
hardware-backed, what the properties of the key pair are, and what
  constraints are applied to its usage and validity. </p>

<p>Apps and off-device services can request information about a key pair
through an X.509 attestation certificate which must be signed by a valid
attestation key. The attestation key is an ECDSA signing key which is
injected into the device’s hardware-backed keystore at the factory.
Therefore, an attestation certificate signed by a valid attestation
key confirms the existence of a hardware-backed keystore, along with
  details of key pairs in that keystore.</p>

<p>To ensure that the device is using a secure, official Android factory
image, Key Attestation requires that the device <a
class="external-link"
href="https://source.android.com/security/verifiedboot/verified-boot.html#bootloader_requirements">bootloader</a>
provide the following information to the <a class="external-link"
href="https://source.android.com/security/trusty/index.html">Trusted
Execution Environment (TEE)</a>:</p>

<ul>
<li>The OS version and patch level installed on the device</li>
<li>The <a href="https://source.android.com/security/verifiedboot/index.html"
class="external-link" >Verified Boot</a> public key and lock status</li>
  </ul>

<p>For more information about the hardware-backed keystore feature,
see the guide for <a href="https://source.android.com/security/keystore/"
class="external-link">Hardware-backed Keystore</a>.</p>

<p>In addition to Key Attestation, Android N also introduces
  fingerprint-bound keys that are not revoked on fingerprint enrollment.</p>

<h2 id="network_security_config">Network Security Config</h2>

<p>In Android N, apps can customize the behavior of their secure (HTTPS, TLS)
connections safely, without any code modification, by using the declarative
<em>Network Security Config</em> instead of using the conventional
error-prone programmatic APIs (e.g. X509TrustManager).</p>

  <p>Supported features:</p>
<ul>
<li><b>Custom trust anchors.</b> Lets an application customize which
Certificate Authorities (CA) are trusted for its secure connections. For
example, trusting particular self-signed certificates or a restricted set of public CAs.
</li>
<li><b>Debug-only overrides.</b> Lets an application developer safely debug
secure connections of their application without added risk to the installed
base.
</li>
<li><b>Cleartext traffic opt-out.</b> Lets an application protect itself from
accidental usage of cleartext traffic.</li>
<li><b>Certificate pinning.</b> An advanced feature that lets an application
  limit which server keys are trusted for secure connections.</li>
</ul>

<p>For more information, see <a
href="{@docRoot}preview/features/security-config.html">Network Security
Config</a>.</p>

<h2 id="default_trusted_ca">Default Trusted Certificate Authority</h2>

<p>By default, apps that target Android N only trust system-provided certificates
and no longer trust user-added Certificate Authorities (CA). Apps targeting Android
N that wish to trust user-added CAs should use the
<a href="{@docRoot}preview/features/security-config.html">Network Security Config</a> to
specify how user CAs should be trusted.</p>

<h2 id="apk_signature_v2">APK signature scheme v2</h2>

<p>
  Android N introduces APK Signature Scheme v2, a new app-signing scheme that
  offers faster app install times and more protection against unauthorized
  alterations to APK files. By default, Android Studio 2.2 and the Android
  Plugin for Gradle 2.2 sign your app using both APK Signature Scheme v2 and
  the traditional signing scheme, which uses JAR signing.
</p>

<p>
  Although we recommend applying APK Signature Scheme v2 to your app, this new
  scheme is not mandatory. If your app doesn't build properly when using APK
  Signature Scheme v2, you can disable the new scheme. The disabling process
  causes Android Studio 2.2 and the Android Plugin for Gradle 2.2 to sign your
  app using only the traditional signing scheme. To sign with only the
  traditional scheme, open the module-level <code>build.gradle</code> file, then
  add the line <code>v2SigningEnabled false</code> to your release signing
  configuration:
</p>

<pre>
  android {
    ...
    defaultConfig { ... }
    signingConfigs {
      release {
        storeFile file("myreleasekey.keystore")
        storePassword "password"
        keyAlias "MyReleaseKey"
        keyPassword "password"
        <strong>v2SigningEnabled false</strong>
      }
    }
  }
</pre>

<p class="caution"><strong>Caution: </strong> If you sign your app using APK
  Signature Scheme v2 and make further changes to the app, the app's signature
  is invalidated. For this reason, use tools such as <code>zipalign</code>
  before signing your app using APK Signature Scheme v2, not after.
</p>

<p>
  For more information, read the Android Studio documents that describe how to
  <a href="{@docRoot}studio/tools/publishing/app-signing.html#release-mode">
  sign an app</a> in Android Studio and how to <a href=
  "{@docRoot}studio/tools/building/configuring-gradle.html#signing"> configure
  the build file for signing apps</a> using the Android Plugin for Gradle.
</p>

<h2 id="scoped_directory_access">Scoped directory access</h2>

<p>In Android N, apps can use new APIs to request access to specific <a
href="{@docRoot}guide/topics/data/data-storage.html#filesExternal">external
storage</a> directories, including directories on removable media such as SD
cards. The new APIs greatly simplify how your application accesses standard
external storage directories, such as the <code>Pictures</code> directory. Apps
like photo apps can use these APIs instead of using
<code>READ_EXTERNAL_STORAGE</code>, which grants access to all storage
directories, or the Storage Access Framework, which makes the user navigate to
the directory.</p>

<p>Additionally, the new APIs simplify the steps a user takes to grant external
storage access to your app. When you use the new APIs, the system uses a simple
permissions UI that clearly details what directory the application is
requesting access to.</p>

<p>For more information, see the
<a href="{@docRoot}preview/features/scoped-folder-access.html">Scoped
Directory Access</a> developer documentation.</p>

<h2 id="print_svc">Print Service Enhancements</h2>

<p>
  In Android N, print service developers can now surface additional information
  about individual printers and print jobs.
</p>

<p>
  When listing individual printers, a print service can now set per-printer
  icons in two ways:
</p>

<ul>
  <li>You can set an icon from a resource ID by calling
  <code>PrinterInfo.Builder.setResourceIconId()</code>
  </li>

  <li>You can show an icon from the network by calling
  <code>PrinterInfo.Builder.setHasCustomPrinterIcon()</code>, and setting a
  callback for when the icon is requested using
  <code>android.printservice.PrinterDiscoverySession.onRequestCustomPrinterIcon()</code>
  </li>
</ul>

<p>
  In addition, you can provide a per-printer activity to display additional
  information by calling <code>PrinterInfo.Builder.setInfoIntent()</code>.
</p>

<p>
  You can indicate the progress and status of print jobs in the print job
  notification by calling
  <code>android.printservice.PrintJob.setProgress()</code> and
  <code>android.printservice.PrintJob.setStatus()</code>, respectively.
</p>

<p>
  For more information about these methods, see the downloadable <a href=
  "{@docRoot}preview/setup-sdk.html#docs-dl">API Reference</a>.
</p>

<h2 id="virtual_files">Virtual Files</h2>

<p>
  In previous versions of Android, your app could use the Storage Access
  Framework to allow users to select files from their cloud storage accounts,
  such as Google Drive. However, there was no way to represent files that did
  not have a direct bytecode representation; every file was required to provide
  an input stream.
</p>

<p>
  Android N adds the concept of <em>virtual files</em> to the Storage Access
  Framework. The virtual files feature allows your
  {@link android.provider.DocumentsProvider} to return document URIs that can be
  used with an {@link android.content.Intent#ACTION_VIEW} intent even if they
  don't have a direct bytecode representation. Android N also allows you to
  provide alternate formats for user files, virtual or otherwise.
</p>

<p>
  To get a URI for a virtual document in your app, first you create an
  {@link android.content.Intent} to open the file picker UI. Since an app
  cannot directly open a virtual file by using the
  {@link android.content.ContentResolver#openInputStream(Uri) openInputStream()}
  method, your app does not receive any virtual files if you include the
  {@link android.content.Intent#CATEGORY_OPENABLE} category.
</p>

<p>
  After the user has made a selection, the system calls the
  {@link android.app.Activity#onActivityResult onActivityResult()} method.
  Your app can retrieve the URI of the virtual file and get an input stream, as
  demonstrated in the code snippet below.
</p>

<pre>
  // Other Activity code ...

  final static private int REQUEST_CODE = 64;

  // We listen to the OnActivityResult event to respond to the user's selection.
  &#64;Override
  public void onActivityResult(int requestCode, int resultCode,
    Intent resultData) {
      try {
        if (requestCode == REQUEST_CODE &amp;&amp;
            resultCode == Activity.RESULT_OK) {

            Uri uri = null;

            if (resultData != null) {
                uri = resultData.getData();

                ContentResolver resolver = getContentResolver();

                // Before attempting to coerce a file into a MIME type,
                // check to see what alternative MIME types are available to
                // coerce this file into.
                String[] streamTypes =
                  resolver.getStreamTypes(uri, "*/*");

                AssetFileDescriptor descriptor =
                    resolver.openTypedAssetFileDescriptor(
                        uri,
                        streamTypes[0],
                        null);

                // Retrieve a stream to the virtual file.
                InputStream inputStream = descriptor.createInputStream();
            }
        }
      } catch (Exception ex) {
        Log.e("EXCEPTION", "ERROR: ", ex);
      }
  }
</pre>

<p>
  For more information about accessing user files, see the
  <a href="{@docRoot}guide/topics/providers/document-provider.html">Storage
  Access Frameworks guide</a>.
</p>