remember.txt

🧠 Complete Breakdown: How Jetpack Compose’s remember Really Works

Most Android devs use remember, but very few actually understand how it remembers.

Let’s fix that 👇
⚙️ Step 1: remember Function
It’s your entry point for caching state across recompositions.
It checks if your keys (key1, key2, etc.) changed, and if yes — recalculates your value.
remember(key1, key2) { calculation() }
Internally, it calls currentComposer.changed(key) for each key — combining results to decide if recomputation is needed.

🧩 Step 2: changed() — Detecting Key Changes
override fun changed(value: Any?): Boolean {
 return if (nextSlot() != value) {
 updateValue(value)
 true
 } else false
}
- Reads the previous slot value
- Compares with the current one
- If changed → updates slot table + marks invalid
This is how Compose tracks what really changed.

📦 Step 3: cache() — The Caching Core
cache(invalid) {
 // Only runs if keys changed or cache is empty
}
If the cache is valid → returns old value
If invalid → recalculates + updates cache
This is what makes Compose “smart”:
No unnecessary recompositions. Just pure efficiency.

🔄 Step 4: RememberObserver — Lifecycle for Remembered Objects
interface RememberObserver {
 fun onRemembered()
 fun onForgotten()
 fun onAbandoned()
}
You can hook into lifecycle events:
- onRemembered() → setup resources
- onForgotten() → cleanup when removed
- onAbandoned() → cleanup if composition fails
Think of it like lifecycle callbacks for remembered objects.

💡 TL;DR
remember = smart caching across recompositions
- Tracks key changes via changed()
- Stores results in the Slot Table
- Recalculates only when invalid
- Hooks into lifecycle with RememberObserver
It’s the invisible performance hero behind every Compose app 💚

What’s one part of the remember mechanism that surprised you the most? 👇