Tag Archives: Kotlin

Kotlin Momentum for Android and Beyond

Posted by James Lau (@jmslau), Product Manager

Today marks the beginning of KotlinConf 2018 - the largest in-person gathering of the Kotlin community annually. 2018 has been a big year for Kotlin, as the language continues to gain adoption and earn the love of developers. In fact, 27% of the top 1000 Android apps on Google Play already use Kotlin. More importantly, Android developers are loving the language with over 97% satisfaction in our most recent survey. It's no surprise that Kotlin was voted as the #2 most-loved language in the 2018 StackOverflow survey.

Google supports Kotlin as a first-class programming language for Android development. In the past 12 months, we have delivered a number of important improvements to the Kotlin developer experience. This includes the Kotlin-friendly SDK, Android KTX, new Lint checks and various Kotlin support improvements in Android Studio. We have also launched Kotlin support in our official documentation, new flagship samples in Kotlin, a new Kotlin Bootcamp Udacity course, #31DaysOfKotlin and other deep dive content. We are committed to continuing to improve the Kotlin developer experience.

As the language continues to advance, more developers are discovering the benefits of Kotlin across the globe. Recently, we traveled to India and worked with local developers like Zomato to better understand how adopting Kotlin has benefited their Android development. Zomato is a leading restaurant search & discovery service that operates in 24 countries, with over 150 million monthly users. Kotlin helped Zomato reduce the number of lines of code in their app significantly, and it has also helped them find important defects in their app at compile time. You can watch their Kotlin adoption story in the video below.

Android Developer Story: Zomato uses Kotlin to write safer, more concise code.

Going beyond Android, we are happy to announce that the Google Cloud Platform team is launching a dedicated Kotlin portal today. This will help developers more easily find resources related to Kotlin on Google Cloud. We want to make it as easy as possible for you to use Kotlin, whether it's on mobile or in the Cloud.

Google Cloud Platform's Kotlin Homepage

Adopting a new language is a major decision for most companies, and you need to be confident that the language you choose will have a bright future. That's why Google has joined forces with JetBrains and established the Kotlin Foundation. The Foundation will ensure that Kotlin continues to advance rapidly, remain free and stay open. You can learn more about the Kotlin Foundation here.

It's an exciting time to be a Kotlin developer. If you haven't tried Kotlin yet, we encourage you to join this growing global community. You can get started by visiting kotlinlang.org or the Android Developer Kotlin page.

Source: Android Developers Blog

Kotlin Momentum for Android and Beyond

Posted by James Lau (@jmslau), Product Manager

Android Developer Story: Zomato uses Kotlin to write safer, more concise code.

Google Cloud Platform's Kotlin Homepage

Source: Android Developers Blog

Verifying your Google Assistant media action integrations on Android

Posted by Nevin Mital, Partner Developer Relations

The Media Controller Test (MCT) app is a powerful tool that allows you to test the intricacies of media playback on Android, and it's just gotten even more useful. Media experiences including voice interactions via the Google Assistant on Android phones, cars, TVs, and headphones, are powered by Android MediaSession APIs. This tool will help you verify your integrations. We've now added a new verification testing framework that can be used to help automate your QA testing.

The MCT is meant to be used in conjunction with an app that implements media APIs, such as the Universal Android Music Player. The MCT surfaces information about the media app's MediaController, such as the PlaybackState and Metadata, and can be used to test inter-app media controls.

The Media Action Lifecycle can be complex to follow; even in a simple Play From Search request, there are many intermediate steps (simplified timeline depicted below) where something could go wrong. The MCT can be used to help highlight any inconsistencies in how your music app handles MediaController TransportControl requests.

Previously, using the MCT required a lot of manual interaction and monitoring. The new verification testing framework offers one-click tests that you can run to ensure that your media app responds correctly to a playback request.

Running a verification test

To access the new verification tests in the MCT, click the Test button next to your desired media app.

The next screen shows you detailed information about the MediaController, for example the PlaybackState, Metadata, and Queue. There are two buttons on the toolbar in the top right: the button on the left toggles between parsable and formatted logs, and the button on the right refreshes this view to display the most current information.

By swiping to the left, you arrive at the verification tests view, where you can see a scrollable list of defined tests, a text field to enter a query for tests that require one, and a section to display the results of the test.

As an example, to run the Play From Search Test, you can enter a search query into the text field then hit the Run Test button. Looks like the test succeeded!

Below are examples of the Pause Test (left) and Seek To test (right).

MCT Screenshot of the right screen in the Testing view for UAMP; a Pause test was run successfully.

MCT Screenshot of the right screen in the Testing view for UAMP; a Seek To test was run successfully.

Android TV

The MCT now also works on Android TV! For your media app to work with the Android TV version of the MCT, your media app must have a MediaBrowserService implementation. Please see here for more details on how to do this.

On launching the MCT on Android TV, you will see a list of installed media apps. Note that an app will only appear in this list if it implements the MediaBrowserService.

Selecting an app will take you to the testing screen, which will display a list of verification tests on the right.

Running a test will populate the left side of the screen with selected MediaController information. For more details, please check the MCT logs in Logcat.

Tests that require a query are marked with a keyboard icon. Clicking on one of these tests will open an input field for the query. Upon hitting Enter, the test will run.

To make text input easier, you can also use the ADB command:

adb shell input text [query]

Note that '%s' will add a space between words. For example, the command adb shell input text hello%sworld will add the text "hello world" to the input field.

What's next

The MCT currently includes simple single-media-action tests for the following requests:

Play
Play From Search
Play From Media ID
Play From URI
Pause
Stop
Skip To Next
Skip To Previous
Skip To Queue Item
Seek To

For a technical deep dive on how the tests are structured and how to add more tests, visit the MCT GitHub Wiki. We'd love for you to submit pull requests with more tests that you think are useful to have and for any bug fixes. Please make sure to review the contributions process for more information.

Check out the latest updates on GitHub!

Source: Android Developers Blog

Android Pie SDK is now more Kotlin-friendly

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!

Source: Android Developers Blog

A New Universal Music Player

Posted by Nicole Borrelli, Android Developer, Programs Engineer

The Universal Android Music Player (or "UAMP") is a favorite on GitHub for music app developers with over 9,500 stars and 3,000 forks. Since UAMP was first released, Android development has changed significantly. ExoPlayer has improved, Architecture Components were introduced, and Kotlin became a first-class language for Android developers.

We decided that the best way to integrate the modern features for our beloved music app would be to re-write UAMP.

UAMP v2 was built from the ground up in Kotlin. The UI is built around ViewModels and LiveData. Playback, and particularly integration with MediaSessionCompat, was vastly simplified by utilizing the MediaSession extension of ExoPlayer.

We also added a bunch of new songs by The Kyoto Connection and Kai Engel.

There are some features from UAMP v1 that haven't been integrated into the new code yet. The missing features include Android TV with the Leanback library and remote playback via Google Cast. Even though these features aren't yet included in v2, we wanted to show you the new updates as soon as possible. The old code will continue to be available in the v1 branch on GitHub, so please take a look there to see how to use those features in a music app.

We would love your feedback on which features to add next. We are considering offline playback, improving the integration with Android Auto, and using the upcoming Navigation components of Jetpack for the UI. We'll be creating GitHub issues for features and improvements to help you let us know what is most important to you. Go vote on these features to let us know where we should focus our efforts.

We'd also like to invite you to open pull requests for bug fixes and features that are missing. See the contributions process for more information.

Grab the code from GitHub!

Source: Android Developers Blog

Learn Kotlin Fast with new Kotlin Bootcamp course

Posted by Aleks Haecky, Training Developer & Word Artist, Google+, LinkedIn, Medium

The Kotlin Bootcamp Udacity course is a free, self-paced online course that teaches you the basics of the Kotlin programming language. This introduction to Kotlin was created by Google experts in collaboration with Udacity and is for people who already know how to program.

The Kotlin language lets you create apps in less time, writing less code, and with fewer errors.

This modern object-oriented language offers a strong type system, type inference, null safety, properties, lambdas, extensions, coroutines, higher-order functions, and many other features. Kotlin is so concise that you can create complete data classes with a single line of code.

Kotlin is officially supported for building Android apps, fully interoperates with the Java programming language and libraries, and is included with IntelliJ and Android Studio.

In this course you will learn everything you need to program in Kotlin, including:

Basics: Write Kotlin statements and expressions in the IntelliJ REPL Kotlin interpreter using nullable and non-nullable variables, data types, operators, and control structures.
Functions: Create a main() function, create and call functions with default and variable arguments, pass functions as arguments to filters, program simple lambdas, function types, and compact single-expression functions.
Classes: Create a class with methods and properties. Implement constructors and init(). Learn about inheritance, interfaces, and abstract classes. Use the special purpose classes data, object, enum, and sealed.
Beyond the Basics: Dive deeper into Pairs, collections, and constants. Learn how to write extensions, implement generics, apply annotations, and use labeled breaks.
Functional Manipulation: Explore more about lambdas, higher-order functions, and inline.

You'll learn how to use extension functions to add helpful functionality to existing classes.

Extend built-in types:

fun Int.print() = println(this)
5.print() // prints 5

Extend Android classes:

fun Context.toast(text: CharSequence, duration: Int = Toast.LENGTH_SHORT): Toast {
   return Toast.makeText(this, text, duration).apply { show() }
}
toast("Hello Toast")

Extend your own classes:

class AquariumPlant(
       val color: String)

fun AquariumPlant.print() =
       println("Pretty Aquarium Plant")

val plant = AquariumPlant("green")
plant.print()
// prints -> Pretty Aquarium Plant

When you've completed the course, you will be able to create programs in Kotlin, taking advantage of the features and capabilities that make Kotlin unique.

The course is available free, online at Udacity; take it in your own time at your own pace.

Go learn how to build apps with less code at https://www.udacity.com/course/ud9011.

Source: Android Developers Blog

Introducing Android KTX: Even Sweeter Kotlin Development for Android

Posted by Jake Wharton (@JakeWharton), Florina Muntenescu (@FMuntenescu) & James Lau (@jmslau)

Today, we are announcing the preview of Android KTX - a set of extensions designed to make writing Kotlin code for Android more concise, idiomatic, and pleasant. Android KTX provides a nice API layer on top of both Android framework and Support Library to make writing your Kotlin code more natural.

The portion of Android KTX that covers the Android framework is now available in our GitHub repo. We invite you to try it out to give us your feedback and contributions. The other parts of Android KTX that cover the Android Support Library will be available in upcoming Support Library releases.

Let's take a look at some examples of how Android KTX can help you write more natural and concise Kotlin code.

Code Samples Using Android KTX

String to Uri

Let's start with this simple example. Normally, you'd call Uri.parse(uriString). Android KTX adds an extension function to the String class that allows you to convert strings to URIs more naturally.

Kotlin	Kotlin with Android KTX
val uri = Uri.parse(myUriString)	val uri = myUriString.toUri()

Edit SharedPreferences

Editing SharedPreferences is a very common use case. The code using Android KTX is slightly shorter and more natural to read and write.

Kotlin	Kotlin with Android KTX
sharedPreferences.edit() .putBoolean(key, value) .apply()	sharedPreferences.edit { putBoolean(key, value) }

Translating path difference

In the code below, we translate the difference between two paths by 100px.

Kotlin

Kotlin with Android KTX

val pathDifference = Path(myPath1).apply {
   op(myPath2, Path.Op.DIFFERENCE)
}

val myPaint = Paint()

canvas.apply {
   val checkpoint = save()
   translate(0F, 100F)
   drawPath(pathDifference, myPaint)
   restoreToCount(checkpoint)
}

val pathDifference = myPath1 - myPath2

canvas.withTranslation(y = 100F) {
   drawPath(pathDifference, myPaint)
}

Action on View onPreDraw

This example triggers an action with a View's onPreDraw callback. Without Android KTX, there is quite a bit of code you need to write.

Kotlin

view.viewTreeObserver.addOnPreDrawListener(
       object : ViewTreeObserver.OnPreDrawListener {
           override fun onPreDraw(): Boolean {
               viewTreeObserver.removeOnPreDrawListener(this)
               actionToBeTriggered()
               return true
           }
       })

Kotlin with Android KTX

view.doOnPreDraw { actionToBeTriggered() }

There are many more places where Android KTX can simplify your code. You can read the full API reference documentation on GitHub.

Getting Started

To start using Android KTX in your Android Kotlin projects, add the following to your app module's build.gradle file:

repositories {
    google()
}

dependencies {
    // Android KTX for framework API
    implementation 'androidx.core:core-ktx:0.1'
    ...
}

Then, after you sync your project, the extensions appear automatically in the IDE's auto-complete list. Selecting an extension automatically adds the necessary import statement to your file.

Beware that the APIs are likely to change during the preview period. If you decide to use it in your projects, you should expect breaking changes before we reach the stable version.

androidx: Hello World!

You may notice that Android KTX uses package names that begin with androidx. This is a new package name prefix that we will be using in future versions of Android Support Library. We hope the division between android.* and androidx.* makes it more obvious which APIs are bundled with the platform, and which are static libraries for app developers that work across different versions of Android.

What's Next?

Today's preview launch is only the beginning. Over the next few months, we will iterate on the API as we incorporate your feedback and contributions. When the API has stabilized and we can commit to API compatibility, we plan to release Android KTX as part of the Android Support Library.

We look forward to building Android KTX together with you. Happy Kotlin-ing!

Source: Android Developers Blog

Update on Kotlin for Android

Posted by James Lau, Product Manager (twitter.com/jmslau)

Today is the beginning of KotlinConf. It's been almost 6 months since we announced Kotlin as a first-class language for Android at Google I/O. During this period, the number of apps on Google Play using Kotlin has more than doubled. More than 17% of the projects in Android Studio 3.0 are now using Kotlin. We are really excited about the strong momentum, and we are thrilled that Android developers all over the world are discovering the joy of Kotlin programming.

Kotlin for Android is production-ready. From startups to Fortune 500 companies, developers are already using Kotlin to build their apps. Developers from Pinterest, to Expedia, to Basecamp -- and many others -- are finding their use of Kotlin is increasing productivity and their overall developer happiness levels. Take a look at some of their experiences with Kotlin below.

With the recent release of Android Studio 3.0, there is now a stable version of our IDE that has Kotlin support built-in. With Support Library 27, we have started adding nullability annotations to make the APIs friendlier to use in Kotlin. We recently published the Android Kotlin Guides on GitHub to provide some guidance for Android Kotlin style and interop. We have also been porting some of our Android samples to Kotlin, and we are adding Kotlin to our official documentation.

Android Studio 3.0

Last week, we released Android Studio 3.0 on the stable channel. This is the first stable release of Android Studio that has Kotlin support built-in. Building on the strength of IntelliJ's Kotlin support, many critical IDE features like code completion and syntax highlighting work well for Kotlin. You can choose to convert Java code to Kotlin by using Code → Convert Java File to Kotlin File, or you can convert snippets of code just by pasting Java code into a Kotlin file.

Project and code templates have also been updated with Kotlin support. When you create a new project or add a new code file, you can choose Kotlin as one of the language options.

The tooling experience with Kotlin is by no means perfect yet. We are aware of several known issues, and we will continue to improve the IDE support for Kotlin in future releases.

Android Kotlin Guides

There are two separate Android Kotlin Guides:

Style guide - details a set of rules and coding standards that Google recommends when writing Kotlin for Android. The guide addresses naming conventions, formatting, structure of the source contents, and much more.
Interop guide - provides a set of rules for creating APIs in the Java and Kotlin programming languages, so that the consuming code in the other language will feel idiomatic.

We intend these guides to be living documents and will evolve them over time. They are hosted on GitHub and we welcome your contributions.

Nullability Annotations

Null-safety is an important feature of the Kotlin language. It helps developers avoid NullPointerExceptions and improves the quality of their apps. Null-safety is a bit more complicated when using Java code from Kotlin. Since any reference in Java may be null, Kotlin's requirement for strict null-safety becomes impractical for Java objects. Types declared in Java that do not contain nullability annotations are called platform types - this means the Kotlin compiler does not know whether it is nullable or not. When calling methods with variables of platform types, the Kotlin compiler relaxes null-safety checks. That means the overall null-safety of your app is weakened.

To let developers take more advantage of Kotlin's strict null-safety, we have started adding nullability annotations in Support Library 27. The Support Library contains a huge API surface area, and we will continue to expand the nullability annotation coverage in the next several releases. In addition, we will also be adding nullability annotations to other Android APIs over time.

While the Kotlin adoption growth is fantastic, our commitment to the Java and C++ programming languages remains unchanged. We've added Java 8 language features support in Android Studio 3.0, and we've added more Java 8 language APIs in Android Oreo. We are also continuing to improve our support for C++17 in the NDK. So even if you are not using Kotlin, your language support will continue to improve.

It's an exciting time to be an Android developer. If you haven't had a chance to try Kotlin, you can get started by learning the basic syntax and by playing with the excellent Kotlin Koans. When you are ready to use Kotlin in your Android app, you can jump to the Android Kotlin page for more resources. With Kotlin's Java interoperability and Android Studio's Java to Kotlin converter, it's easy to start using Kotlin in your project.

Happy Kotlin-ing!

Source: Android Developers Blog

Kotlin and the Google Mobile Ads SDK

One of the biggest cheers from the crowd at I/O '17 came in response to Stephanie Saad Cuthbertson's announcement that Kotlin would be an officially supported language for Android development starting with Android Studio 3.0. If you're an AdMob or Doubleclick publisher who's been eager to make the leap to a new language, we've got another announcement you might like: now that the new version of Android Studio has launched, we've released bunch of new mobile ads resources to support the Kotlin community.

If you haven't seen Kotlin yet, it's a statically typed language developed by JetBrains that compiles down to the same JVM bytecode that Java does, but includes a number of new features that can make Android development faster and easier. Things like dedicated data classes with less boilerplate, the Elvis operator, lambdas, SAM conversion, explicit nullability for references, and lots of other modern language features come built-in. For more information, see Introduction to Kotlin (also from I/O '17) in which Andrey Breslav and Hadi Hariri code up examples of the language's best features:

When you're done, you can see those same features in action in our new developer resources, which are now available to the AdMob and Doubleclick publisher community.

Samples

The Mobile Ads DevRel team maintains a GitHub repository of Android samples covering our API, and we've pushed Kotlin versions for each ad format. If you been wondering how Kotlin's Android extensions work with AdMob's banner ad layouts, for example, we've got a new sample app that'll show you. If you're curious how native ads work with all the new nullability stuff, we've got you covered with Kotlin samples for those formats as well.

In addition, we've included a new version of our API Demo app, which features a navigation drawer full of individual API demos for things like banner sizes, category exclusions, and more, all in Kotlin.

Implementation Guides

We've also updated our publisher guides with Kotlin snippets wherever code is shown. Similar to the mobile ads guides for iOS (which show either Swift or Objective-C syntax with a click of a tab), the Android guides now let developers easily switch back and forth between Java and Kotlin implementations.

Questions?

If you take a look at the Kotlin guides and samples and find you've got questions about the best way to implement something in Android's first ever new language, stop by our support forum. Our staff there will be happy to help.

- Andrew Brogdon, Mobile Ads Developer Relations

Source: Google Ads Developer Blog

Kotlin and the Google Mobile Ads SDK

When you're done, you can see those same features in action in our new developer resources, which are now available to the AdMob and Doubleclick publisher community.

Samples

Implementation Guides

Questions?

- Andrew Brogdon, Mobile Ads Developer Relations