Jorge Castillo

Android devs coming to teach you Dependency Injection in 2025.

Android devs coming to teach you Dependency Injection in 2025.

1-star reviews hurt. Especially the random ones.

But I’ve learned to stop fighting them.
Just keep improving the product until they get absolutely drowned out by the 5-star ones.

Let quality win.

My main goal when creating the Compose internals course was for people to walk away knowing how Compose *really* works.

The target is curious devs that are tired of copying patterns they don’t understand.

If you want a course about the basic stuff, the official docs are good 🤷‍♂️

Remember when Spider-Man tried to write an Android app 🕸️

Not many people mentions this.

Developers love best practices, because thinking is hard.

But great engineers know when to break them, bend them, or create new ones. If you ever invented a pattern from scratch,
you’re already in the 1% of actually creative people that can make things evolve.

If you want to be 5 years ahead of everyone else:

Stop treating frameworks like black boxes.

Read the source. Understand the internals.
You’ll stop guessing and start building with intention 🫡

There’s so much I can share about Compose, but it’s impossible and unbearable to do it all on X.

For the full content, book the Jetpack Compose Internals course. I promise you will not regret 🙌

composeinternals.com

The recomposer coordinates all of this, deciding when and on what thread to compose and when and on what thread to apply the changes.

Hope it was useful 🫡

The Composer (injected by the Compiler in all Composable functions) uses the notes recorded in the slot table (from last composition) to produce the next change list that updates the tree, in every recomposition.

The change list (emitted by Composables when they execute) is what updates the node tree. You can think of it as a patch file for the node tree that, when applied, updates the tree. The tree is built during composition, and gets updated on every recomposition.

In Compose, the slot table contains notes about what happened during composition, what was called, what parameters were used, etc.. It is where values are remembered and you can think of it as a method trace of the composition 🧵

We all suspected what the Lofi Girl was doing.

Toughest part of Android development isn’t learning Compose, mastering architecture or improving performance.

It is fragmentation. It has always been.

Thinking about it retrospectively, we put the biggest % of our time fighting that while testing, debugging and monitoring.

The Jetpack Compose Internals course has been on fire lately. More and more devs are giving super constructive feedback every day.

I honestly appreciate it, since talking about complex topics in simple terms is not easy. Took some good amount of effort and exploration to get there 🫶

Writing tests is part of the work.

You don’t report “I wrote tests” in standup
Just like you don’t say “I wrote code that compiles” or “I wrote an abstraction”.

Unless the culture expects you to brag about it for some weird reason.

How to kill the vibe 101

Setting up Compose Multiplatform previews Compose Multiplatform now has support for previews in common code. Here's how you can get started with using them.

How to setup previews in Compose Multiplatform.

https://zsmb.co/compose-multiplatform-preview-setup/

Apps like Duolingo are more like a game that makes you feel progress. But the real way to learn a language is having to speak it every day. Nothing better than real world conversations with others. That’s a great use case for AI too.

Don’t feel bad for not learning new technologies quickly. You are all skilled more than enough to learn it quickly whenever you need to.

Don’t fall in the trap. FOMO is common but also irrational.

Share a piece of lore about your Android dev career

Share a piece of lore about your Android dev career

The official Android docs on test doubles are quite needed today. Please write fakes 🙏 , avoid mocks as possible. Assert output state, not behavior. Think of a program or a logical part of it as: input->output https://developer.android.com/training/testing/fundamentals/test-doubles

The official Android docs on test doubles are quite needed today.

Please write fakes 🙏 , avoid mocks as possible. Assert output state, not behavior. Think of a program or a logical part of it as: input->output

https://developer.android.com/training/testing/fundamentals/test-doubles

Sometimes you need to give people a little push

Sometimes you need to give people a little push

In Compose, each item in a LazyColumn is rendered through subcomposition.

– It’s a separate child composition
– It has its own slot table for storing state
– That slot table can be reused later if the item scrolls back in (as long as the key is stable)

Always focus on the end goals, don’t get distracted by technologies or patterns. If you are not meeting your end goal expectations then you’re doing it wrong.

Example: Measure performance, not number of recompositions.

Tests are only useful if they catch regressions. If that is never the case for you, then think again what type of tests you have.

I forget about this constantly.

If you get a warning about one of your apps in the Google Play developer console, keep in mind that it could be caused by any of the releases published to any of your active tracks, even the testing ones (open or closed).

KMP

KMP

Sometimes you just need to look at things differently.

You’re tired, but it’s from work you once wished for. You’re overwhelmed, but it’s by the growth you used to hope for. You’re challenged, but it’s by a life you chose. You’ve outgrown things you once thought were enough. That’s progress.

Exploring PausableComposition internals in Jetpack Compose Explore the internals of the `PausableComposition` API in Jetpack Compose to improve UI performance by pre-composing elements during idle time in Android

Compose added something wild:

PausableComposition lets the runtime start composing UI before it’s needed, split across idle frames, and pause/resume mid way. Really interesting to explore 🧐

https://blog.shreyaspatil.dev/exploring-pausablecomposition-internals-in-jetpack-compose

Things have changed a bit.

Things have changed a bit.