jetc.dev Newsletter Issue #83

Published: 2021-09-21

1.1.0-alpha04 was released, bringing the oft-requested Kotlin 1.5.30 support! 🎉

Beyond that, we look at getting common concerns in migrating to Compose UI: getting at Intent extras and showing classic dialogs. We look at form validation, drop-down menus, and palettes. We see a sweet KSP annotation processor to help with Navigation for Compose. And I take a glance at some work-in-progress Compose libraries for app widgets and Wear OS tiles.

Alpha Analysis

Reviewing the release notes for the latest Jetpack Compose update!

Beyond the Kotlin 1.5.30 support, 1.1.0-alpha04 has a few changes, including:

There has been a fair bit of change with touch events, such as the deprecation of GestureScope and the addition of performTouchInput()
Android 12 stretch overscroll is now supported

One Off the Stack, One Off the Slack

You’ve got questions. That’s understandable!

How to Get Intent Data in a Composable

Just because you are using Compose UI does not change many of the fundamental needs of Android app development. But the fact that Compose UI encourages pure functions means that to fulfill those needs you need to wade through a seemingly-endless set of CompositionLocal values. So, if you want to get the extras delivered to your Intent, you will need to work with LocalContext, as we see in this week’s highlighted Stack Overflow question.

How Do We Show a Non-Compose Dialog?

Similarly, you may have the need to integrate with existing UI elements — perhaps from third-party libraries — that are stuck in the activity/fragment/view system. To show a classic Dialog from a composable, you can use DisposableEffect(), as we see in this week’s highlighted Kotlinlang #compose Slack thread.

Composable Commentary

Posts, videos, and other new information related to Jetpack Compose!

Video: Compose: The Future of Native Android UI Development

Google’s Anna-Chiara Bellini delivered a presentation with a high-level overview of the role of Compose, how basic composables work, where Compose is going, and how you can get started.

Medium: Basic Form Validation in Android with Jetpack Compose

Two years ago, Brandon Wever wrote a Medium post on form validation using data binding and LiveData. Brandon rewrote that post to use Compose UI, while retaining the same ViewModel and LiveData that was used in the original post.

How to Test Jetpack Compose

Testing! We really should do some of that! In this post, Dmytro tours the mechanics of testing our composables using ComposeTestRule (for testing composables in isolation) and AndroidComposeTestRule (for testing composables in an activity).

Accessibility in Compose - Supporting Dynamic Font Sizes

Joe Birch returns, looking at how we can deal with scalable text sizes. The Text() composable and MaterialTheme() work in sp units… but what about the composables around your text? Joe examines using modifiers such as widthIn() to have your outer composables handle text scaling according to your design rules.

How to master Swipeable and NestedScroll modifiers in Jetpack Compose

Angelo Marchesin needed a bottom sheet with some particular behaviors, just enough that the stock implementations were not quite right. In this post, Angelo looks at how to create a bottom sheet, particularly one that not only expands and collapses but has scrollable content as well.

Rob Kerr wanted a classic overflow menu in a Compose UI TopAppBar(). Rob shows how to implement that, using DropdownMenu().

Composing palettes

Thomas Künneth is back, this time looking at the Palette library for extracting theme-like colors from the contents of a Bitmap, and seeing how we can apply that in a composable.

Resource Roundup

100% pure code!

GitHub: raamcosta / compose-destinations

Rafael Costa created a KSP processor that lets you create Navigation for Compose routes via @Destination annotations on composables. It determines arguments from the actual composable function arguments, including support for default values, and deep links.

GitHub: jisungbin / ComposeMultiFab

Ji Sungbin created a floating action menu (FAB with a fly-out set of choices), in the form of a MultiFloatingActionButton() composable. It supports icons and optional labels, custom tints, and more.

GitHub: pz64 / RoundedStarShape-JetPack-Compose

Compose UI has nice support for applying Shape objects to things like a Surface(), but there are only so many built in shapes. GitHub user pz64 has a library with two more: a rounded star and a polygon.

GitHub: timeline-notes / compose-mathjax

If you need to render LaTeX math functions, the Timeline Notes team ported an earlier function rendering library to Compose UI.

…And One More Thing

Back at Google I|O 2021, as part of the “Compose all the things” theme, Google showed some sample code for creating app widgets via composables. I reviewed that code and pointed out that while we might use Compose for app widgets, Compose UI — at least as we use it for Android and desktop — was unrealistic.

Dylan Roussel pointed out that Google is creating a “Glance” library that seems reminiscent of the sample code from I|O. We get a set of composables that resembles a tiny subset of Compose UI, and those get mapped to corresponding constructs in a RemoteViews.

Android Code Search shows three modules:

glance, containing core code
glance-appwidget, containing the RemoteViews composables for app widgets
glance-wear, for Wear OS tiles

These in turn depend on other things that do not yet exist as published artifacts. glance-appwidget depends on a core-remoteviews library, for example. However, as expected, none of these depend on Compose UI, just the Compose compiler and runtime.

Instead, Glance has its own composables for Box(), Column(), Row(), and Text(), along with related modifiers and classes. The same composable API is used for both app widgets and Wear OS tiles, as far as I can tell.

These projects have interesting elements in their implementations. They serve as yet more examples of how to apply Compose in non-traditional use cases. Also, glance-appwidget has an AppWidgetHostRule for writing instrumented tests for app widgets, and it seems like it might be usable beyond these Compose-crafted app widgets.

It is nice to see that Google is continuing work on the API they previewed at I|O!

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