Let's render a simple page with Ktor server and kotlinx.html: get("/users.html") { call.respondHtml { myLayout(title = "Users") { userList( users = db.users.value, ) } } } A reusable myLayout provides scaffolding, userList encapsulates the specific page content, and db.users is a StateFlow<List<User...

Two months ago I gave my first ever live programming talk at KotlinConf. It was called "Talking to terminals (and how they talk back)", and you can watch it here. I've previously done slide-heavy talks which contained small demos or navigating through an existing codebase. Since this talk was starti...

I'm happy to announce that Retrofit, OkHttp, and Okio are moving to a new GitHub organization, and along with SQL Delight are all joining the Commonhaus Foundation. You can read their announcement of the move. This move is meant to reinforce our commitment to these projects' longevity and honor the ...

Eight years ago we launched a library of Kotlin extensions for the Android platform, Android KTX. In the time since, the library became Core KTX, and numerous other KTX libraries were written for other AndroidX libraries. And while KTX's approach to adding Kotlin niceties was built on a strong techn...

Many people rely on the Compose bill of materials (BOM) artifact to provide the complete set of Compose dependency versions. If we use Compose’s foundation 1.8.0 but a transitive dependency bumps foundation-layout, there’s a risk that these two versions are incompatible with each other despite other...

Did you know the versioning of AndroidX libraries and their stability guarantees are different from most libraries? Their betas and RCs are actually production-ready, and you should be using them! In a “normal” library, such as the ones I release, features are added and known bugs are fixed to produ...

I used to use Bit.ly to put links into my presentations. Their service allowed you to customize the path portion of the link, so I was able to create links like bit.ly/ok-libs. If you were attending the talks live, watching the recording, or browsing the slides, the short URL was easy to type into a...

It doesn't take long for a project to spawn multiple jobs in their GitHub Actions. Parallelization can lead to huge speedups for PRs. Job grouping makes it easier to conditionally enable or disable multiple steps. Each time you add a new job, however, you have to mark it as required in branch protec...

JNI allows managed code inside the JVM or ART to call into native code. Java methods can be declared as native, and then a corresponding C function1 can be written and automatically wired together when the native library is loaded. Native code lacks mechanisms like packages and overloads, so a speci...

When Espresso was made public a decade ago, one of its banner features was the "idling resource" concept. This monitored the main thread and any background thread pools to prevent your test from progressing until the app became idle. Waiting until idle generally increased the stability of tests sinc...

You want to be using the latest JDK for development. Don't use Gradle toolchains, they'll needlessly force you to use old JDKs. You can still target and test on old JVM versions but develop with the latest and greatest. Java and the JDK are literally built for this. Locally this hasn't been a proble...

There was a time when I used Maven heavily, but today all the libraries I work on build with Gradle. Even though I'm publishing with Gradle, consumers can use Gradle, Maven, Bazel, jars in libs/ (but please don't), or anything else. That's a huge JVM ecosystem win! In general, I don't have to think ...

The last post featured some Kotlin code inadvertently targeting a new Java API when the build JDK was bumped to 21. This can be solved with the -Xjdk-release Kotlin compiler flag, or by using Gradle toolchains to build with an old JDK. If you read the Gradle docs… Using Java toolchains is a preferre...

Yesterday, our Android app crashed with a weird NoSuchMethodError. java.lang.NoSuchMethodError: No interface method removeFirst()Ljava/lang/Object; in class Ljava/util/List; or its super classes (declaration of 'java.util.List' appears in /apex/com.android.art/javalib/core-oj.jar) at app.cash.redwoo...

Given an array of integers ([1, 2, 3, 1, 3, 1]), find the elements which are duplicated. No, we're not interviewing. I'm trying to prevent a user from specifying a reserved value twice. Elsewhere in the file I already have duplicate detection for object tags. val dupes: Map<Int, List<Widget>> = widg...

Given a list of users, extract their names and join them into a comma-separated list. Kotlin's extension functions on collections make this trivial. users.map { it.name }.joinToString() Writing this in IntelliJ IDEA produces a "weak warning" offering advice. Call chain on collection type may be simp...

This post was published externally on Cash App Code Blog. Read it at https://code.cash.app/molecule-1-0.

This post was published externally on Cash App Code Blog. Read it at https://code.cash.app/native-ui-and-multiplatform-compose-with-redwood.

This post was published externally on Cash App Code Blog. Read it at https://code.cash.app/flow-testing-with-turbine.

jlink is a JDK tool to create bespoke, minimal JREs for your applications. Let's try it with a "Hello, world!" program: class Main { public static void main(String... args) { System.out.println("Hello, world!"); } } My laptop is an M1 Mac and I have downloaded the Azul Zulu JDK 19 build for it. With...

Three years ago I gave the talk "What's new in Java 19: The end of Kotlin?" which forecasted what a future Java language would look like in September 2022 when Java 19 was released. Check your calendars, folks. It's September 2022 right now and Java 19 was released today! As expected my predictions ...

In the past, when a new version of Java was released, I would add that version to our open source project's CI builds. strategy: matrix: java-version: - 8 - 9 ⋮ - 17 + - 18 This ensures that each project can be built and its tests pass on every major version. But this makes no sense! No user is buil...

The equation y=mx+b defines a line in slope-intercept form. The line will intercept the y-axis at the value b and for each change in x its slope (the amount the line goes up or down) will change by m. Slope-intercept gives me a way to think about the design of libraries in relation to each other. Th...

This post was published externally on Cash App Code Blog. Read it at https://code.cash.app/the-state-of-managing-state-with-compose.

My primary work project for the better part of a year (named Redwood) is built on top of Compose1 and runs on every platform that Kotlin supports. This of course means Android, but we also have Compose running on iOS, the web, the JVM, and all other native targets. It's truly a multiplatform Compose...

This post was published externally on Cash App Code Blog. Read it at https://code.cash.app/gradle-dependency-license-validation.

Having been burned by case-insensitive filesystem bugs one too many times, I long ago switched my development folder to a case-sensitive filesystem partition on my otherwise case-insensitive Mac. Unfortunately this can actually work against me as I interact with the computers of coworkers and servic...

Earlier this year I built a web-based garage door controller using Rust for the Raspberry Pi called Normally Closed. My deployment includes a Pi 3b and a Pi Zero which are ARMv7 and ARMv6 devices, respectively. I deploy services with Docker and wanted to continue using it here for simplicity. Gettin...

This post was published externally on Cash App Code Blog. Read it at https://code.cash.app/migrating-from-burst-to-testparameterinjector.

One of my favorite non-features from building view binding is that it lacks integration with activities or fragments. If you use view binding with activities or fragments, however, this fact might be to your disdain. Every activity using view binding is forced to do something along the lines of: ove...