From XML mutations to declarative magic. How Jetpack Compose reshaped how we think about Android UI.
Intro
Most of us build with Jetpack Compose today, but few of us pause to ask why it changed everything.
In this post, I’ll share how my own Android journey (from Java + XML projects to modern Compose apps) helped me see what truly makes declarative UI different, and why it quietly reshaped how we design, debug, and think about Android.
👨💻 My Journey: From XML Mutations to Compose Mindset
When I started Android development back in October 2021, I started with the roots, my world was all XML and Java.
My first apps LearnHindi and ShortNews were classic View-based projects: findViewById(), adapters, and endless setText() calls.
It was exciting, but also fragile.
Every UI update felt like diffusing a bomb. You change one thing, break three others.
Then I switched to Kotlin, and eventually Jetpack Compose and suddenly, it felt like I was building with Android, not fighting it.
Compose wasn’t just new syntax. It was a new way of thinking.
💡 Compose Didn’t Just Replace XML, it Replaced How We Think About UI
Compose made our UIs faster to build, but its real gift was predictability.
For the first time, the UI became a pure reflection of state, not a pile of mutable views.
“UI is a function of state.”
That’s the line that changed everything.
No more juggling references or wondering if the screen updated correctly.
Now the question was simple: What should this screen look like for the current state?
🧠 Declarative vs Imperative: The Core Idea You Already Use (But Might Not Have Named)
| Concept | Imperative (Old View System) | Declarative (Compose) |
|---|---|---|
| UI model | Mutable tree of Views | Pure function returning UI |
| State flow | Push data manually | UI reacts automatically |
| Ownership | You own updates | Compose owns invalidations |
| Mental model | “When should I update?” | “What should UI look like now?” |
You already write this daily:
@Composable
fun ProfileCard(user: User) {
Text(text = user.name)
}
You don’t “set” anything, you describe it.
The function’s output is your UI; Compose handles when and how it changes.
⚙️ Why Declarative UIs Scale Better
In XML days:
textView.text = "Online"
progressBar.visibility = View.GONE
You were mutating an object graph while keeping mental tabs on every widget.
In Compose:
if (user.isOnline) Text("Online")
else CircularProgressIndicator()
You simply describe what the UI should be, and Compose ensures the screen stays true to state.
That’s why scaling from simple screens to complex, multi-source UIs is finally sane.
🔬 Under the Hood (2025 Edition)
By 2025, Compose’s runtime has matured into a highly optimized diff engine.
The compiler tracks which values change and triggers recomposition only where needed.
You can see it in:
@Stable / @Immutable annotations guiding recomposition
The new Modifier.Node system improving performance
Recomposition tracing built into Layout Inspector (AGP 8.12+)
No hacks, no boilerplate, just a solid, state-driven UI pipeline.
🧩 The Real Lesson for Compose Developers
If you’re already using Compose, your next level isn’t learning more APIs, it’s learning to think declaratively across your architecture.
That means:
Let state drive everything and no manual “UI updates.”
Keep composables pure: inputs in, visuals out.
Hoist state properly so logic and UI stay predictable.
Once you adopt that mindset you'll see that testing, previews, and animations stop being chores, they just work.
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