Category : Kotlin

Posted by James Lau, Product Manager (@jmslau)

When using the Java programming language, one of the most common pitfalls is trying to access a member of a null reference, causing a NullPointerException to be thrown. Kotlin offers protection against this by baking nullable and non-nullable types into the type system. This helps eliminate NullPointerExceptions from your code and improve your app’s overall quality. When Kotlin code is calling into APIs written in the Java programming language, it relies on nullability annotations in those APIs to determine the nullability of each parameter and the return type. Unannotated parameters and return types are treated as platform types, which weakens the null-safety guarantee of Kotlin.

As part of yesterday’s Android 9 announcement, we have also released a new Android SDK that contains nullability annotations for some of the most frequently used APIs. This will preserve the null-safety guarantee when your Kotlin code is calling into any annotated APIs in the SDK. Even if you are using the Java programming language, you can still benefit from these annotations by using Android Studio to catch nullability contract violations.

Not a breaking change

Normally, nullability contract violations in Kotlin result in compilation errors. But to ensure the newly annotated APIs are compatible with your existing code, we are using an internal mechanism provided by the Kotlin compiler team to mark the APIs as recently annotated. Recently annotated APIs will result only in warnings instead of errors from the Kotlin compiler. You will need to use Kotlin 1.2.60 or later.

Our plan is to have newly added nullability annotations produce warnings only, and increase the severity level to errors starting in the following year’s Android SDK. The goal is to provide you with sufficient time to update your code.

How to use the “Kotlin-friendly” SDK

To get started, go to Tools > SDK Manager in Android Studio. Select Android SDK on the left menu, and make sure the SDK Platforms tab is open.

Use SDK Manager in Android Studio to install SDK for API Level 28 Revision 6

Check Android 8.+ (P) and click OK. This will install the Android SDK Platform 28 revision 6 if it is not already installed. After that, set your project’s compile SDK version to API 28 to start using the new Android Pie SDK with nullability annotations.

Use the Project Structure Dialog to change your project’s Compile Sdk Version to API 28

You may also need to update your Kotlin plugin in Android Studio if it’s not already up-to-date. Make sure your Kotlin plugin version is 1.2.60 or later by going to Tools > Kotlin > Configure Kotlin Plugin Updates.

Once it’s set up, your builds will start showing warnings if you have any code that violates nullability contracts in the Android SDK. An example of such a warning is shown below.

Sample warning from the Kotlin compiler when code violates a
recently added nullability contract in the Android SDK.

You will also start seeing warnings in Android Studio’s code editor if you call an Android API with the incorrect nullability. An example is shown below.

Android Studio warning about passing a null reference to a parameter
annotated as a recently non-null type in the android.graphics.Path API.

Leveraging nullability annotations from the Java programming language

You can benefit from the new nullability annotations even if your code is in the Java programming language. By default, Android Studio will highlight any nullability contract violations with a warning, like the one below:

Android Studio showing a warning about nullability contract violation
in code written in the Java programming language

To ensure that you have this inspection enabled, you can go to the IDE’s settings page and search for “Constant conditions & exceptions” inspection and make sure that item is checked.

Use the Inspections page under Settings to ensure the Constant conditions & exceptions code inspection is enabled.

If you are using the Java programming language, nullability contract violations will not produce any compiler warning or error. Only the in-IDE code inspections are available to flag these issues.

You can also run code inspections across your entire project and see the aggregated results. Click on Analyze > Inspect Code… to start.

What’s Next

The Android SDK API surface is very large, and we have only annotated a small percentage of the APIs so far – there is still lots of work remaining. Over the next several Android SDK releases, we will continue to add nullability annotations to the existing Android APIs, as well as making sure new APIs are annotated.

With the “Kotlin-friendly” Android SDK, the nullability annotations in AndroidX (part of the Jetpack family), and Android KTX, we are continuing to improve the Android APIs for developers using Kotlin. If you have not yet tried Kotlin, we encourage you to try it. Not only can Kotlin make your code more concise, it can also improve the stability of your apps.

Happy Kotlin-ing!

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Posted By Stephanie Cuthbertson, Product Management Director, Android

As Android has grown exponentially over the past ten years, we’ve also seen our developer community grow dramatically. In countries like China, India, and Brazil, the number of developers using our IDE almost tripled – in just two years. With such growth, we feel an even greater responsibility to invest in our developer experience. Guided by your feedback, we’ve focused our efforts on making mobile development fast and easy, helping you get more users by making apps radically smaller, and increasing engagement to keep users coming back. We’re also pretty excited to see Android Things go to 1.0, creating new opportunities for you to develop – everything from major consumer devices, to cool remote control vehicles! As Day 1 of Google I/O kicks off, let’s take a closer look at these major themes from the Developer Keynote:

Development: making mobile development fast and easy

  • Android Jetpack — Today, we announced Android Jetpack, designed to accelerate your app development. Android Jetpack is the next generation of Android components, bringing together the benefits of the Support Library — backwards compatibility and immediate updates — to a larger set of components, making it quick and easy to build robust, high quality apps. Android Jetpack manages activities like background tasks, navigation, and lifecycle management, so you can eliminate boilerplate code and focus on what makes your app great. Android Jetpack is designed to work well with Kotlin, saving you even more code with Android KTX. The new Android Jetpack components released today include WorkManager, Paging, Navigation, and Slices.

  • Kotlin — Since announcing support for Kotlin last year, the developer community has embraced the language. Most importantly, 95% of developers tell us they are very happy with using Kotlin for their Android development. And, the more developers use it, the more that number rises. The number of Play Store apps using Kotlin grew 6x in the last year. 35% of pro developers use it, and that number is growing each month. We are continuing to improve the Kotlin developer experience across our libraries, tooling, runtime, documentation and training. Android KTX is launching today as part of Android Jetpack to optimize the Kotlin developer experience. Tooling continues to improve with Android Studio, Lint support, and R8 optimizations. We have even tuned the Android Runtime (ART) in Android P, so that apps built with Kotlin can run faster. We have rolled out Kotlin code snippets in our official documentation, and are publishing a Kotlin version of the API reference documentation today. Earlier this week, we launched a new Kotlin Bootcamp on Udacity, which is a great resource for developers who are new to Kotlin. Lastly, we now have a Kotlin specialization in the Google Developers Experts Program. If you still haven’t used Kotlin, I hope you you give it a try.
  • Android Studio 3.2 CanaryAndroid Studio 3.2 features tools for Android Jetpack including a visual Navigation Editor and new code refactoring tools. The canary release also includes build tools to create the new Android App Bundle format, Snapshots in the Android Emulator for fast start time, new R8 optimizer for smaller download and install app code size, a new Energy Profiler to measure app impact on battery life, and more. You can download the latest version of Android Studio 3.2 from the canary channel download page.

Distribution: making apps radically smaller

Introducing Android App Bundle.

  • Android App Bundle & Google Play Dynamic Delivery — Introducing the new app model for Android. Dramatically reduce app size with a new publishing format—the Android App Bundle. In Android Studio, you’ll now build an app bundle that contains everything your app needs for any device—all the languages, every device screen size, every hardware architecture. Then, when a user downloads your app, Google Play’s new Dynamic Delivery will only deliver the code and resources matching the user’s device. People see a smaller install size on the Play Store, can download your app more quickly, and save space on their devices. An example of all resources being delivered to a device via a legacy APK and an example of Dynamic Delivery serving just what’s needed to a device.
    (Left) An example of all resources being delivered to a device via a legacy APK.
    (Right) An example of Dynamic Delivery serving just what’s needed to a device.
  • Dynamic features via the Android App Bundle — The Android App Bundle also enables modularization so that you can deliver features on-demand, instead of during install. You can build dynamic feature modules in the latest Android Studio canary release. Join our beta program to publish them on Google Play.
  • Google Play Console — New features and reports in the Play Console will help you improve your app’s performance and grow your business. Read about the improvements to the dashboard, statistics, Android vitals, pre-launch report, acquisition report, and subscriptions dashboard. You can also upload, test, and publish apps using our new publishing format, the Android App Bundle.
  • Google Play Instant — After launching in beta at GDC, today we announced that all game developers can build instant apps and we’re thrilled to welcome Candy Crush Saga. Google Play Instant is now available on over 1 billion devices worldwide from the Play Store, search, social and most places you can tap a link. To make instant apps easier to build, we are launching a Unity plugin and beta integration with Cocos creator this week. Recently, we’ve started testing Google Play Instant compatibility with AdWords, allowing people to try out games directly from ads, across all the channels reached by Universal App campaigns.

Engagement: bringing users back more and more.

  • Slices Slices are UI templates that display a rich array of dynamic, and interactive content from your app, across Android and within Google surfaces. Slices can include live-data, scrolling content, inline actions, and deep-linking into your app so users can do everything from playing music to checking reservation updates. Slices can also contain interactive controls like toggles and sliders. You can get started building Slices today, and they will begin appearing for users soon.
Check reservations with Slices.Control music with Slices.Call a Lyft using Slices.
  • Actions — Actions are a new way to make your app’s capabilities and content more accessible, so that people can easily get to it at the right moment. App Actions will appear to users based on usage and relevance, across multiple Google and Android surfaces, such as the Google Search App, the Play Store, the Google Assistant, and the Launcher. App Actions will be available for all developers to try soon, please sign up here if you’d like to be notified. You can also choose to build a Conversational Action as a companion experience to your app. This works on a variety of Assistant-enabled devices, such as speakers and smart displays. Both types of Actions use a new common catalog of intents.

Actions are a new way to make your app's capabilities and content more accessible, so that people can easily get to it at the right moment.

Smarter devices: a powerful platform for IoT devices

  • Android Things 1.0 Android Things is Google’s managed OS that enables developers to build and maintain Internet of Things devices at scale. Earlier this year at CES, we announced Lenovo, Harman, LG, and iHome are all building Assistant-enabled products powered by Android Things. Introducing Android Things 1.0! After a developer preview with over 100,000 SDK downloads and feedback from more than 10,000 developers, we announced Android Things 1.0 this week. Four new System-on-Modules (SoMs) are now supported on the platform with guaranteed long-term support for three years and additional options for extended support, making it easier to go from prototypes to production. To make product development more seamless than ever, the accompanying Android Things Console is also ready for production. It helps developers easily manage and update their devices with the latest stability fixes and security updates provided by Google.

To get started with Android Things, visit our developer site and the new Community Hub to explore kits, sample code, community projects, and join Google’s IoT Developers Community to stay updated. We introduced a limited program to partner with the Android Things team for technical guidance and support building your product. If your company is interested, sign up for our OEM Partner Program.
In addition to all these new developments, we’re on the ground in over 140 countries, growing and expanding the developer community through programs such as Women Techmakers and Google Developer Groups (GDGs). We’re investing in training programs like Google Developers Certification, building more courses through Udacity and other partners, to help developers deepen their technical capability. Today, 225 Google Developers Agency Program members from 50 agencies in 15 countries, are Android Certified. As part of our Google Developers Experts Program, we also now have more than 90 Android Developer Experts around the world actively supporting developers, start-ups and companies to build and launch innovative apps.
We also continue to recognize the great work from top app and game developers. This year, we held our third annual Google Play Awards. The nominees represent some of the best experiences available on Android, with an emphasis on overall quality, strong design, technical performance, and innovation. Check out the winners and nominees.
During Google I/O, attendees and viewers have an opportunity to dive deep with 48 Android & Play breakout sessions. Thank you for all your wonderful feedback, and please keep giving us your advice on where we should go next.