Posted by Sam Dutton, Ankur Kotwal, Developer Advocates; Liz Yepsen, Program Manager
‘TOP-UP WARNING.’ ‘NO CONNECTION.’ ‘INSUFFICIENT BANDWIDTH TO PLAY THIS RESOURCE.’
These are common warnings for many smartphone users around the world.
To build products that work for billions of users, developers must address key challenges: limited or intermittent connectivity, device compatibility, varying screen sizes, high data costs, short-lived batteries. We first presented developers.google.com/billions and related Android and Web resources at Google I/O last month, and today you can watch the video presentations about Android or the Web.
These best practices can help developers reach billions by delivering exceptional performance across a range of connections, data plans, and devices. g.co/dev/billions will help you:
Seamlessly transition between slow, intermediate, and offline environments
Your users move from place to place, from speedy wireless to patchy or expensive data. Manage these transitions by storing data, queueing requests, optimizing image handling, and performing core functions entirely offline.
Provide the right content for the right context
Keep context in mind - how and where do your users consume your content? Selecting text and media that works well across different viewport sizes, keeping text short (for scrolling on the go), providing a simple UI that doesn’t distract from content, and removing redundant content can all increase perception of your app’s quality while giving real performance gains like reduced data transfer. Once these practices are in place, localization options can grow audience reach and increase engagement.
Optimize for mobile hardware
Ensure your app or Web content is served and runs well for your widest possible addressable market, covering all actively used OS versions, while still following best practices, by testing on virtual or actual devices in target markets. Native Android apps should set minimum and target SDKs. Also, remember low cost phones have smaller amounts of RAM; apps should therefore adjust usage accordingly and minimize background running. For in-depth information on minimizing APK size, check out this series of Medium posts. On the Web, optimize JavaScript CPU usage, avoid raster image rendering, and minimize resource requests. Find out more here.
Reduce battery consumption
Low cost phones usually have shorter battery life. Users are sensitive to battery consumption levels and excessive consumption can lead to a high uninstall rate or avoidance of your site. Benchmark your battery usage against sessions on other pages or apps, or using tools such as Battery Historian, and avoid long-running processes which drain batteries.
Conserve data usage
Whatever you’re building, conserve data usage in three simple steps: understand loading requirements, reduce the amount of data required for interaction, and streamline navigation so users get what they want quickly. Conserving data on behalf of your users (and with native apps, offering configurable network usage) helps retain data-sensitive users -- especially those on prepaid plans or contracts with limited data -- as even “unlimited” plans can become expensive when roaming or if unexpected fees are applied.
Have another insight, or a success launching in low-connectivity conditions or on low-cost devices? Let us know on our G+ post.
Posted by Tamzin Taylor - Strategic Partner Lead, Google Play
Watch the video series to learn:
You can also get the News Publisher Playbook on the Play Store to help you develop a successful news mobile strategy on Android. It includes tips on mobile website optimization, how to create a Google Play Newsstand edition, how to improve your native app, and more.
Give us your feedback
Once you’ve checked out the video series, we’d love to hear your feedback so we can continue to help you find success with and achieve your business objectives. Leave a comment or a thumbs up, and subscribe to the Android Developers YouTube channel!
Also, check out our other videos in in the Tips for Success on Google Play series, including the recent video on 10 tips to build an app for billions of users.
For more best practices to find success on Google Play, get the new Playbook for Developers app.
Posted by Dmitry Malykhanov, Developer Advocate
Related to other improvements to the Android platform, the dynamic linker in Android M and N has stricter requirements for writing clean, cross-platform compatible native code in order to load. It is necessary that an application’s native code follows the rules and recommendations in order to ensure a smooth transition to recent Android releases.
Below we outline in detail each individual change related to native code loading, the consequences and steps you can take to avoid issues.
Required tools: there is an <arch>-linux-android-readelf binary (e.g. arm-linux-androideabi-readelf or i686-linux-android-readelf) for each architecture in the NDK (under toolchains/), but you can use readelf for any architecture, as we will be doing basic inspection only. On Linux you need to have the “binutils” package installed for readelf, and “pax-utils” for scanelf.
Native libraries must use only public API, and must not link against non-NDK platform libraries. Starting with API 24 this rule is enforced and applications are no longer able to load non-NDK platform libraries. The rule is enforced by the dynamic linker, so non-public libraries are not accessible regardless of the way code tries to load them: System.loadLibrary(...), DT_NEEDED entries, and direct calls to dlopen(...) will fail in exactly the same way.
Users should have a consistent app experience across updates, and developers shouldn’t have to make emergency app updates to handle platform changes. For that reason, we recommend against using private C/C++ symbols. Private symbols aren’t tested as part of the Compatibility Test Suite (CTS) that all Android devices must pass. They may not exist, or they may behave differently. This makes apps that use them more likely to fail on specific devices, or on future releases --- as many developers found when Android 6.0 Marshmallow switched from OpenSSL to BoringSSL.
In order to reduce the user impact of this transition, we’ve identified a set of libraries that see significant use from Google Play’s most-installed apps, and that are feasible for us to support in the short term (including libandroid_runtime.so, libcutils.so, libcrypto.so, and libssl.so). In order to give you more time to transition, we will temporarily support these libraries; so if you see a warning that means your code will not work in a future release -- please fix it now!
$ readelf --dynamic libBroken.so | grep NEEDED 0x00000001 (NEEDED) Shared library: [libnativehelper.so] 0x00000001 (NEEDED) Shared library: [libutils.so] 0x00000001 (NEEDED) Shared library: [libstagefright_foundation.so] 0x00000001 (NEEDED) Shared library: [libmedia_jni.so] 0x00000001 (NEEDED) Shared library: [liblog.so] 0x00000001 (NEEDED) Shared library: [libdl.so] 0x00000001 (NEEDED) Shared library: [libz.so] 0x00000001 (NEEDED) Shared library: [libstdc++.so] 0x00000001 (NEEDED) Shared library: [libm.so] 0x00000001 (NEEDED) Shared library: [libc.so]
Potential problems: starting from API 24 the dynamic linker will not load private libraries, preventing the application from loading.
Resolution: rewrite your native code to rely only on public API. As a short term workaround, platform libraries without complex dependencies (libcutils.so) can be copied to the project. As a long term solution the relevant code must be copied to the project tree. SSL/Media/JNI internal/binder APIs should not be accessed from the native code. When necessary, native code should call appropriate public Java API methods.
A complete list of public libraries is available within the NDK, under platforms/android-API/usr/lib.
platforms/android-API/usr/lib
Note: SSL/crypto is a special case, applications must NOT use platform libcrypto and libssl libraries directly, even on older platforms. All applications should use GMS Security Provider to ensure they are protected from known vulnerabilities.
Each ELF file has additional information contained in the section headers. These headers must be present now, because the dynamic linker uses them for sanity checking. Some developers try to strip them in an attempt to obfuscate the binary and prevent reverse engineering. (This doesn’t really help because it is possible to reconstruct the stripped information using widely-available tools.)
$ readelf --header libBroken.so | grep 'section headers' Start of section headers: 0 (bytes into file) Size of section headers: 0 (bytes) Number of section headers: 0 $
Resolution: remove the extra steps from your build that strip section headers.
Starting with API 23, shared objects must not contain text relocations. That is, the code must be loaded as is and must not be modified. Such an approach reduces load time and improves security.
The usual reason for text relocations is non-position independent hand-written assembler. This is not common. Use the scanelf tool as described in our documentation for further diagnostics:
$ scanelf -qT libTextRel.so libTextRel.so: (memory/data?) [0x15E0E2] in (optimized out: previous simd_broken_op1) [0x15E0E0] libTextRel.so: (memory/data?) [0x15E3B2] in (optimized out: previous simd_broken_op2) [0x15E3B0] [skipped the rest]
If you have no scanelf tool available, it is possible to do a basic check with readelf instead, look for either a TEXTREL entry or the TEXTREL flag. Either alone is sufficient. (The value corresponding to the TEXTREL entry is irrelevant and typically 0 --- simply the presence of the TEXTREL entry declares that the .so contains text relocations). This example has both indicators present:
$ readelf --dynamic libTextRel.so | grep TEXTREL 0x00000016 (TEXTREL) 0x0 0x0000001e (FLAGS) SYMBOLIC TEXTREL BIND_NOW $
Note: it is technically possible to have a shared object with the TEXTREL entry/flag but without any actual text relocations. This doesn’t happen with the NDK, but if you’re generating ELF files yourself make sure you’re not generating ELF files that claim to have text relocations, because the Android dynamic linker trusts the entry/flag.
Potential problems: Relocations enforce code pages being writable, and wastefully increase the number of dirty pages in memory. The dynamic linker has issued warnings about text relocations since Android K (API 19), but on API 23 and above it refuses to load code with text relocations.
Resolution: rewrite assembler to be position independent to ensure no text relocations are necessary. Check the Gentoo documentation for cookbook recipes.
While library dependencies (DT_NEEDED entries in the ELF headers) can be absolute paths, that doesn’t make sense on Android because you have no control over where your library will be installed by the system. A DT_NEEDED entry should be the same as the needed library’s SONAME, leaving the business of finding the library at runtime to the dynamic linker.
Before API 23, Android’s dynamic linker ignored the full path, and used only the basename (the part after the last ‘/’) when looking up the required libraries. Since API 23 the runtime linker will honor the DT_NEEDED exactly and so it won’t be able to load the library if it is not present in that exact location on the device.
Even worse, some build systems have bugs that cause them to insert DT_NEEDED entries that point to a file on the build host, something that cannot be found on the device.
$ readelf --dynamic libSample.so | grep NEEDED 0x00000001 (NEEDED) Shared library: [libm.so] 0x00000001 (NEEDED) Shared library: [libc.so] 0x00000001 (NEEDED) Shared library: [libdl.so] 0x00000001 (NEEDED) Shared library: [C:\Users\build\Android\ci\jni\libBroken.so] $
Potential problems: before API 23 the DT_NEEDED entry’s basename was used, but starting from API 23 the Android runtime will try to load the library using the path specified, and that path won’t exist on the device. There are broken third-party toolchains/build systems that use a path on a build host instead of the SONAME.
Resolution: make sure all required libraries are referenced by SONAME only. It is better to let the runtime linker to find and load those libraries as the location may change from device to device.
Each ELF shared object (“native library”) must have a SONAME (Shared Object Name) attribute. The NDK toolchain adds this attribute by default, so its absence indicates either a misconfigured alternative toolchain or a misconfiguration in your build system. A missing SONAME may lead to runtime issues such as the wrong library being loaded: the filename is used instead when this attribute is missing.
$ readelf --dynamic libWithSoName.so | grep SONAME 0x0000000e (SONAME) Library soname: [libWithSoName.so] $
Potential problems: namespace conflicts may lead to the wrong library being loaded at runtime, which leads to crashes when required symbols are not found, or you try to use an ABI-incompatible library that isn’t the library you were expecting.
Resolution: the current NDK generates the correct SONAME by default. Ensure you’re using the current NDK and that you haven’t configured your build system to generate incorrect SONAME entries (using the -soname linker option).
-soname
Please remember, clean, cross-platform code built with a current NDK should have no issues on Android N. We encourage you to revise your native code build so that it produces correct binaries.
Posted by Michael Sipe, Product Manager
As an important framework for finding objects in photos and video, Mobile Vision operation for Android devices is restored in Google Play Services v9.2.
This new version of Google Play Services fixes a download issue in Google Play Services v.9.0 that caused a service outage. See release notes for details.
We’re also pleased to announce the Text API, a new component for Android Mobile Vision.
The Text API’s optical character recognition technology reads Latin character text (e.g. English, Spanish, German, French, etc.) in photos and returns the text as well as the organizational structure (paragraphs, lines, words). Mobile apps can now:
If you want to get started quickly, you can try our codelab which will get Android developers reading text with their apps in under an hour.
Like the Mobile Vision Face and Barcode components, the Text API runs on-device and is suitable for real-time applications. For more information, check out the Mobile Vision Developer site.
Posted by Bhavik Singh, Product Manager
Last month at Google I/O 2016 we announced the new Google Awareness APIs, enabling your apps to intelligently react to user context using snapshots and fences with minimal impact on system resources.
Today we’re proud to announce that the Google Awareness API is available to all developers through Google Play services.
Using 7 different types of context—including location, weather, user activity, and nearby beacons—your app can better understand your users’ current situations, and use this information to provide optimized and customized experiences.
The Awareness API offers two ways to take advantage of context signals within your app:
As a single, simplified surface, the Awareness APIs combine optimally processed context signals in new ways that were not previously possible, providing more accurate and insightful context cues, while also managing system resources to save battery and minimize bandwidth.
We’ve worked closely with some of our partners, who have already found amazing ways to integrate context awareness into their apps:
Trulia, an online residential real estate site, uses our Fence API to suggest open houses. When the weather is perfect and the user is walking around near a house they are interested in, Trulia sends a notification reminding them to stop by. This sort of tailored notification can help users engage with open houses at the perfect time for them.
SuperPlayer Music, on the other hand, uses our Snapshot API and Fence API to suggest the perfect music to match your mood. Whether you’re just finishing up a run and beginning to stretch, setting off on a long car ride, or just getting to the gym, their assistant can understand your context and suggest the right playlist for you.
With our initial set of signals and our awesome partners, we’re just getting started with the Awareness APIs. Join us on a journey to build tailored experiences within your apps, by getting started with the Google Awareness API developer documentation, and learn more by watching our Google I/O session
Posted by Shanea King-Roberson, Lead Program Manager Twitter: @shaneakr Instagram: @theshanea
Do you have an idea for an app but you don’t know where to start? There are over 1 billion Android devices worldwide, providing a way for you to deliver your ideas to the right people at the right time. Google, in partnership with Udacity, is making Android development accessible and understandable to everyone, so that regardless of your background, you can learn to build apps that improve the lives of people around you.
Enroll in the new Android Basics Nanodegree. This series of courses and services teaches you how to build simple Android apps--even if you have little or no programming experience. Take a look at some of the apps built by our students:
The app "ROP Tutorial" built by student Arpy Vanyan raises awareness of a potentially blinding eye disorder called Retinopathy of Prematurity that can affect newborn babies.
And user Charles Tommo created an app called “Dr Malaria” that teaches people ways to prevent malaria.
With courses designed by Google, you can learn skills that are applicable to building apps that solve real world problems. You can learn at your own pace to use Android Studio (Google’s official tool for Android app development) to design app user interfaces and implement user interactions using the Java programming language.
The courses walk you through step-by-step on how to build an order form for a coffee shop, an app to track pets in a shelter, an app that teaches vocabulary words from the Native American Miwok tribe, and an app on recent earthquakes in the world. At the end of the course, you will have an entire portfolio of apps to share with your friends and family.
Upon completing the Android Basics Nanodegree, you also have the opportunity to continue your learning with the Career-track Android Nanodegree (for intermediate developers). The first 50 participants to finish the Android Basics Nanodegree have a chance to win a scholarship for the Career-track Android Nanodegree. Please visit udacity.com/legal/scholarship for additional details and eligibility requirements. You now have a complete learning path to help you become a technology entrepreneur or most importantly, build very cool Android apps, for yourself, your communities, and even the world.
All of the individual courses that make up this Nanodegree are available online for no charge at udacity.com/google. In addition, Udacity provides paid services, including access to coaches, guidance on your project, help staying on track, career counseling, and a certificate upon completion for a fee.
You will be exposed to introductory computer science concepts in the Java programming language, as you learn the following skills.
To enroll in the Android Basics Nanodegree program, click here.
See you in class!
Posted by Dimitry Ivanov & Elliott Hughes, Software Engineers
As documented in the Android N behavioral changes, to protect Android users and apps from unforeseen crashes, Android N will restrict which libraries your C/C++ code can link against at runtime. As a result, if your app uses any private symbols from platform libraries, you will need to update it to either use the public NDK APIs or to include its own copy of those libraries. Some libraries are public: the NDK exposes libandroid, libc, libcamera2ndk, libdl, libGLES, libjnigraphics, liblog, libm, libmediandk, libOpenMAXAL, libOpenSLES, libstdc++, libvulkan, and libz as part of the NDK API. Other libraries are private, and Android N only allows access to them for platform HALs, system daemons, and the like. If you aren’t sure whether your app uses private libraries, you can immediately check it for warnings on the N Developer Preview.
We’re making this change because it’s painful for users when their apps stop working after a platform update. Whether they blame the app developer or the platform, everybody loses. Users should have a consistent app experience across updates, and developers shouldn’t have to make emergency app updates to handle platform changes. For that reason, we recommend against using private C/C++ symbols. Private symbols aren’t tested as part of the Compatibility Test Suite (CTS) that all Android devices must pass. They may not exist, or they may behave differently. This makes apps that use them more likely to fail on specific devices, or on future releases — as many developers found when Android 6.0 Marshmallow switched from OpenSSL to BoringSSL.
You may be surprised that there’s no STL in the list of NDK libraries. The three STL implementations included in the NDK — the LLVM libc++, the GNU STL, and libstlport — are intended to be bundled with your app, either by statically linking into your library, or by inclusion as a separate shared library. In the past, some developers have assumed that they didn’t need to package the library because the OS itself had a copy. This assumption is incorrect: a particular STL implementation may disappear (as was the case with stlport, which was removed in Marshmallow), may never have been available (as is the case with the GNU STL), or it may change in ABI incompatible ways (as is the case with the LLVM libc++).
In order to reduce the user impact of this transition, we’ve identified a set of libraries that see significant use from Google Play’s most-installed apps, and that are feasible for us to support in the short term (including libandroid_runtime.so, libcutils.so, libcrypto.so, and libssl.so). For legacy code in N, we will temporarily support these libraries in order to give you more time to transition. Note that we don't intend to continue this support in any future Android platform release, so if you see a warning that means your code will not work in a future release — please fix it now!
Table 1. What to expect if your app is linking against private native libraries.
Please test your app during the N Previews.
targetSdkVersion
Test your apps on the Developer Preview — if you see a toast like this one, your app is accessing private native APIs. Please fix your code soon!
Here’s some example logcat output from an app that hasn’t bumped its target SDK version (and so the restriction isn’t fully enforced because this is only the developer preview):
03-21 17:07:51.502 31234 31234 W linker : library "libandroid_runtime.so" ("/system/lib/libandroid_runtime.so") needed or dlopened by "/data/app/com.popular-app.android-2/lib/arm/libapplib.so" is not accessible for the namespace "classloader-namespace" - the access is temporarily granted as a workaround for http://b/26394120
This is telling you that your library “libapplib.so” refers to the library “libandroid_runtime.so”, which is a private library.
When Android N ships, or if you set your target SDK version to N now, you’ll see something like this if you try to use System.loadLibrary from Java:
java.lang.UnsatisfiedLinkError: dlopen failed: library "libcutils.so" ("/system/lib/libcutils.so") needed or dlopened by "/system/lib/libnativeloader.so" is not accessible for the namespace "classloader-namespace" at java.lang.Runtime.loadLibrary0(Runtime.java:977) at java.lang.System.loadLibrary(System.java:1602)
If you’re using dlopen(3) from C/C++ you’ll get a NULL return and dlerror(3) will return the same “dlopen failed...” string as shown above.
For more information about how to check if your app is using private symbols, see the FAQ on developer.android.com.
Posted by Dom Elliott, the Google Play team
Here’s how you read and watch content in the Playbook for Developers app:
The app supports Android 5.0 and above. If you're on an older device, check out our ebook, The Secrets to App Success on Google Play. We will be adding and updating content in the app to help you stay up-to-date and grow your business. Get the Playbook for Developers app today and then give us your feedback. The app is also available in the following languages: Bahasa Indonesia, Deutsch, español (Latinoamérica), le français, português do Brasil, tiếng Việt, русский язы́к, 한국어, 中文 (简体), 中文 (繁體), and 日本語.
This is the second app we’ve released for Google Play developers. Get the Google Play Developer Console app to review your app's performance statistics and financial data, get notified about your app's status and publishing changes, and read and reply to user reviews on the go.
Posted by Dave Burke, VP of Engineering
As we put the finishing touches on the next release of Android, which will begin to roll out to consumers later this summer, we’re releasing the 4th Developer Preview of Android N, including the Android N final SDK. And thanks to your continued feedback over the last three releases, all of the APIs are now final as well. If you’ve already enrolled your device in the Android Beta Program, (available at android.com/beta) you will receive an update to this Developer Preview shortly.
The final SDK for Android N is now available for download through the SDK Manager in Android Studio. It gives you everything you need to develop and test against the official APIs in the Android N platform. Once you’ve installed the final SDK, you can update your project’s compileSdkVersion to API 24 to develop with the Android N APIs and build and test on the new platform, for new features such as Multi-window support, direct-reply notifications, and others. We also recommend updating your app’s targetSdkVersion to API 24 to opt-in and test your app with Android N specific behavior changes. For details on how to setup your app with the final SDK, see Set up the Preview. For details on API level 24 check out the API diffs and the updated API reference, now hosted online.
compileSdkVersion
Along with the Android N final SDK, we’ve also updated the Android Support Library to 24.0.0. This allows you to use multi-window and picture-in-picture callbacks, new notification features, methods for supporting Direct Boot, and new MediaBrowser APIs in a backward compatible manner.
Now that you have a final set of APIs, you can publish updates compiling with, and optionally targeting, API 24 to Google Play. You can now publish app updates that use API 24 to your alpha, beta, or even production channels in the Google Play Developer Console. In this way, you can test your app’s backward-compatibility and push updates to users whose devices are running Developer Preview 4.
To make sure that your updated app runs well on Android N, as well as older versions, a common strategy is to use Google Play’s beta testing feature to get early feedback from a small group of users -- including developer preview users — and then do a staged rollout as you release the updated app to all users.
Developer Preview 4 includes updated system images for all supported Preview devices as well as for the Android emulator. If you are already enrolled in the Android Beta program, your devices will get the Developer Preview 4 update right away, no action is needed on your part. If you aren’t yet enrolled in Android Beta, the easiest way to get started is by visiting android.com/beta and opt-in your eligible Android phone or tablet -- you’ll soon receive this (and later) preview updates over-the-air. As always, you can also download and flash this update manually. The N Developer Preview is available for Nexus 6, Nexus 5X, Nexus 6P, Nexus 9, and Pixel C devices, as well as General Mobile 4G [Android One] devices and the Sony Xperia Z3.
Thanks so much for all of your feedback so far. Please continue to share feedback or requests either in the N Developer Preview issue tracker, N Preview Developer community, or Android Beta community as we work towards the consumer release later this summer. We’re looking forward to seeing your apps on Android N!
Sendy is a door to door on-demand couriering platform founded in Nairobi, Kenya. It connects customers and logistics providers, providing two unique apps, one for the driver and one for the customer. Watch CEO & Co-founder, Meshack Alloys, and Android Developer, Jason Rogena, explain how they use Developer Console features, such as alpha and beta testing, as well as other tips and best practices, to build for the next billion users.
Learn more about building for billions and get more tips to grow your games business by opting-in to the Playbook app beta and download the Playbook app in the Google Play Store.
Posted by Sergio Giro, software engineer
If your Android app derives keys using the SHA1PRNG algorithm from the Crypto provider, you must start using a real key derivation function and possibly re-encrypt your data.
The Java Cryptography Architecture allows developers to create an instance of a class like a cipher, or a pseudo-random number generator, using calls like:
SomeClass.getInstance("SomeAlgorithm", "SomeProvider");
Or simply:
SomeClass.getInstance("SomeAlgorithm");
For instance,
Cipher.getInstance(“AES/CBC/PKCS5PADDING”); SecureRandom.getInstance(“SHA1PRNG”);
On Android, we don’t recommend specifying the provider. In general, any call to the Java Cryptography Extension (JCE) APIs specifying a provider should only be done if the provider is included in the application or if the application is able to deal with a possible ProviderNotFoundException.
Unfortunately, many apps depend on the now removed “Crypto” provider for an anti-pattern of key derivation.
This provider only provided an implementation of the algorithm “SHA1PRNG” for instances of SecureRandom. The problem is that the SHA1PRNG algorithm is not cryptographically strong. For readers interested in the details, On statistical distance based testing of pseudo random sequences and experiments with PHP and Debian OpenSSL,Section 8.1, by Yongge Want and Tony Nicol, states that the “random” sequence, considered in binary form, is biased towards returning 0s, and that the bias worsens depending on the seed.
As a result, in Android N we are deprecating the implementation of the SHA1PRNG algorithm and the Crypto provider altogether. We’d previously covered the issues with using SecureRandom for key derivation a few years ago in Using Cryptography to Store Credentials Safely. However, given its continued use, we will revisit it here.
A common but incorrect usage of this provider was to derive keys for encryption by using a password as a seed. The implementation of SHA1PRNG had a bug that made it deterministic if setSeed() was called before obtaining output. This bug was used to derive a key by supplying a password as a seed, and then using the "random" output bytes for the key (where “random” in this sentence means “predictable and cryptographically weak”). Such a key could then be used to encrypt and decrypt data.
In the following, we explain how to derive keys correctly, and how to decrypt data that has been encrypted using an insecure key. There’s also a full example, including a helper class to use the deprecated SHA1PRNG functionality, with the sole purpose of decrypting data that would be otherwise unavailable.
Keys can be derived in the following way:
SecretKey key = new SecretKeySpec(keyBytes, "AES");
/* User types in their password: */ String password = "password"; /* Store these things on disk used to derive key later: */ int iterationCount = 1000; int saltLength = 32; // bytes; should be the same size as the output (256 / 8 = 32) int keyLength = 256; // 256-bits for AES-256, 128-bits for AES-128, etc byte[] salt; // Should be of saltLength /* When first creating the key, obtain a salt with this: */ SecureRandom random = new SecureRandom(); byte[] salt = new byte[saltLength]; random.nextBytes(salt); /* Use this to derive the key from the password: */ KeySpec keySpec = new PBEKeySpec(password.toCharArray(), salt, iterationCount, keyLength); SecretKeyFactory keyFactory = SecretKeyFactory .getInstance("PBKDF2WithHmacSHA1"); byte[] keyBytes = keyFactory.generateSecret(keySpec).getEncoded(); SecretKey key = new SecretKeySpec(keyBytes, "AES");
That's it. You should not need anything else.
To make transitioning data easier, we covered the case of developers that have data encrypted with an insecure key, which is derived from a password every time. You can use the helper class InsecureSHA1PRNGKeyDerivator in the example app to derive the key.
InsecureSHA1PRNGKeyDerivator
private static SecretKey deriveKeyInsecurely(String password, int keySizeInBytes) { byte[] passwordBytes = password.getBytes(StandardCharsets.US_ASCII); return new SecretKeySpec( InsecureSHA1PRNGKeyDerivator.deriveInsecureKey( passwordBytes, keySizeInBytes), "AES"); }
You can then re-encrypt your data with a securely derived key as explained above, and live a happy life ever after.
Note 1: as a temporary measure to keep apps working, we decided to still create the instance for apps targeting SDK version 23, the SDK version for Marshmallow, or less. Please don't rely on the presence of the Crypto provider in the Android SDK, our plan is to delete it completely in the future.
Note 2: Because many parts of the system assume the existence of a SHA1PRNG algorithm, when an instance of SHA1PRNG is requested and the provider is not specified we return an instance of OpenSSLRandom, which is a strong source of random numbers derived from OpenSSL.
Posted by Ian Lake, Developer Advocate
Android notifications are often a make-or-break interaction between your Android app and users. To provide a better user experience, notifications on Android N have received a visual refresh, improved support for custom views, and expanded functionality in the forms of Direct Reply, a new MessagingStyle, and bundled notifications.
MessagingStyle
The first and most obvious change is that the default look and feel of notifications has significantly changed. Many of the fields that were spread around the notifications have been collapsed into a new header row with your app’s icon and name anchoring the notification. This change ensured that the title, text, and large icon are given the most amount of space possible and, as a result, notifications are generally slightly larger now and easier to read.
Given the single header row, it is more important than ever that the information there is useful. When you target Android N, by default the time will be hidden - if you have a time critical notification such as a messaging app, you can re-enable it with setShowWhen(true). In addition, the subtext now supersedes the role of content info and number: number is never shown on Android N devices and only if you target a previous version of Android and don’t include a subtext will content info appear. In all cases, ensure that the subtext is relevant and useful - don’t add an account email address as your subtext if the user only has one account, for example.
setShowWhen(true)
Notification actions have also received a redesign and are now in a visually separate bar below the notification.
You’ll note that the icons are not present in the new notifications; instead more room is provided for the labels themselves in the constrained space of the notification shade. However, the notification action icons are still required and continue to be used on older versions of Android and on devices such as Android Wear.
If you’ve been building your notification with NotificationCompat.Builder and the standard styles available to you there, you’ll get the new look and feel by default with no code changes required.
NotificationCompat.Builder
If you’re instead building your notification from custom RemoteViews, adapting to any new style has been challenging. With the new header, expanding behavior, actions, and large icon positioning as separate elements from the main text+title of the notification, we’ve introduced a new DecoratedCustomViewStyle and DecoratedMediaCustomViewStyle to provide all of these elements, allowing you to focus only on the content portion with the new setCustomContentView() method.
RemoteViews
DecoratedCustomViewStyle
DecoratedMediaCustomViewStyle
setCustomContentView()
This also ensures that future look and feel changes should be significantly easier to adapt to as these styles will be updated alongside the platform with no code changes needed on the app side.
While notification actions have already been able to launch an Activity or do background work with a Service or BroadcastReceiver, Direct Reply allows you to build an action that directly receives text input inline with the notification actions.
Activity
Service
BroadcastReceiver
Direct Reply uses the same RemoteInput API - originally introduced for Android Wear - to mark an Action as being able to directly receive input from the user.
RemoteInput
Action
The RemoteInput itself contains information like the key which will be used to later retrieve the input and the hint text which is displayed before the user starts typing.
// Where should direct replies be put in the intent bundle (can be any string) private static final String KEY_TEXT_REPLY = "key_text_reply"; // Create the RemoteInput specifying this key String replyLabel = getString(R.string.reply_label); RemoteInput remoteInput = new RemoteInput.Builder(KEY_TEXT_REPLY) .setLabel(replyLabel) .build();
Once you’ve constructed the RemoteInput, it can be attached to your Action via the aptly named addRemoteInput() method. You might consider also calling setAllowGeneratedReplies(true) to enable Android Wear 2.0 to generate Smart Reply choices when available and make it easier for users to quickly respond.
addRemoteInput()
setAllowGeneratedReplies(true)
// Add to your action, enabling Direct Reply for it NotificationCompat.Action action = new NotificationCompat.Action.Builder(R.drawable.reply, replyLabel, pendingIntent) .addRemoteInput(remoteInput) .setAllowGeneratedReplies(true) .build();
Keep in mind that the pendingIntent being passed into your Action should be an Activity on Marshmallow and lower devices that don’t support Direct Reply (as you’ll want to dismiss the lock screen, start an Activity, and focus the input field to have the user type their reply) and should be a Service (if you need to do work on a separate thread) or BroadcastReceiver (which runs on the UI thread) on Android N devices so as the process the text input in the background even from the lock screen. (There is a separate user control to enable/disable Direct Reply from a locked device in the system settings.)
pendingIntent
Extracting the text input in your Service/BroadcastReceiver is then possible with the help of the RemoteInput.getResultsFromIntent() method:
RemoteInput.getResultsFromIntent()
private CharSequence getMessageText(Intent intent) { Bundle remoteInput = RemoteInput.getResultsFromIntent(intent); if (remoteInput != null) { return remoteInput.getCharSequence(KEY_TEXT_REPLY); } return null; }
After you’ve processed the text, you must update the notification by calling notify() with the same id and tag (if used). This is the trigger which hides the Direct Reply UI and should be used as a technique to confirm to the user that their reply was received and processed correctly.
notify()
id
tag
For most templates, this should involve using the new setRemoteInputHistory() method which appends the reply to the bottom of the notification. Additional replies should be appended to the history until the main content is updated (such as the other person replying).
setRemoteInputHistory()
However, if you’re building a messaging app and expect back and forth conversations, you should use MessagingStyle and append the additional message to it.
We’ve optimized the experience for displaying an ongoing conversation and using Direct Reply with the new MessagingStyle.
This style provides built-in formatting for multiple messages added via the addMessage() method. Each message supports passing in the text itself, a timestamp, and the sender of the message (making it easy to support group conversations).
addMessage()
builder.setStyle(new NotificationCompat.MessagingStyle("Me") .setConversationTitle("Team lunch") .addMessage("Hi", timestampMillis1, null) // Pass in null for user. .addMessage("What's up?", timestampMillis2, "Coworker") .addMessage("Not much", timestampMillis3, null) .addMessage("How about lunch?", timestampMillis4, "Coworker"));
You’ll note that this style has first-class support for specifically denoting messages from the user and filling in their name (in this case with “Me”) and setting an optional conversation title. While this can be done manually with a BigTextStyle, by using this style Android Wear 2.0 users will get immediate inline responses without kicking them out of the expanded notification view, making for a seamless experience without needing to build a full Wear app.
BigTextStyle
Once you’ve built a great notification by using the new visual designs, Direct Reply, MessagingStyle, and all of our previous best practices, it is important to think about the overall notification experience, particularly if you post multiple notifications (say, one per ongoing conversation or per new email thread).
If you’ve built stacking notifications for Android Wear, the API used here is exactly the same. Simply add setGroup() to each individual notification to bundle those notifications together. You’re not limited to one group, so bundle notifications appropriately. For an email app, you might consider one bundle per account for instance.
setGroup()
It is important to also create a summary notification. This summary notification, denoted by setGroupSummary(true), is the only notification that appears on Marshmallow and lower devices and should (you guessed it) summarize all of the individual notifications. This is an opportune time to use the InboxStyle, although using it is not a requirement. On Android N and higher devices, some information (such as the subtext, content intent, and delete intent) is extracted from the summary notification to produce the collapsed notification for the bundled notifications so you should continue to generate a summary notification on all API levels.
setGroupSummary(true)
InboxStyle
To improve the overall user experience on Android N devices, posting 4 or more notifications without a group will cause those notifications to be automatically bundled.
Notifications on Android have been a constant area of progressive enhancement. From the single tap targets of the Gingerbread era to expandable notifications, actions, MediaStyle, and now features such as Direct Reply and bundled notifications, notifications play an important part of the overall user experience on Android.
With many new tools to use (and NotificationCompat to help with backward compatibility), I’m excited to see how you use them to #BuildBetterApps
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Posted by Lily Sheringham, Google Play team
Based in Ho Chi Minh City in Vietnam, games developer Divmob has grown quickly from an original team of five people to 40 employees since it was founded three years ago. Divmob now has over 40 million downloads across its various titles, including the popular game, Epic Heroes War.
Watch Ngo Van Luyen, CEO & Founder at Divmob, and his team explain how introducing sub-dollar pricing in various markets resulted in a 300% increase in daily transactions, and increased the number of paying users threefold.
Find out more about local pricing models on Google Play
We recently introduced new features in the Google Play Developer Console to help you meet local expectations when setting prices, to make purchases more attractive to your users. The Developer Console will now automatically round pricing to local conventions in each market, and you can also set up pricing templates to manage pricing across multiple currencies more efficiently, and easily make bulk changes to the prices of multiple apps and in-app products in a single click. Learn more about the improved local pricing tools.
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