101 posts
Compose's recommended architecture is three layers with one-directional dependencies. The split inside the UI layer — elements and state holders — is the one that decides whether a screen can be tested without a device.
CompositionLocal passes values down the composition without parameters. That invisibility is the feature and the danger: three tests for when it is the right tool, and what to use instead when it isn't.
remember dies on rotation. rememberSaveable survives rotation and process death by writing into the saved instance state Bundle — which has limits, costs, and a custom-type story worth knowing before you need it.
Correct hoisting can still produce an unmaintainable codebase. The four failure modes that show up once a screen grows past a few components, and the fixes for each.
Hoisting to a ViewModel is a different decision from hoisting to a parent composable. The dividing question is lifetime, and getting it wrong in either direction has a specific cost.
State hoisting means moving state to the lowest common ancestor of everything that needs it. The trigger is a second reader — not a rule to apply preemptively.
Compose renders in three phases. Where you read state decides which phase invalidates, and moving a read from composition into layout or draw is the single highest-leverage performance change available.
A network call written directly in a composable fires an unpredictable number of times. LaunchedEffect, DisposableEffect and SideEffect each define a different notion of when work should happen.
Composables have a lifecycle, but it is nothing like a View's. Three events — enter, recompose, leave — and the identity rules that decide which one you get.
Compose does not re-run your whole screen when state changes. It re-runs the smallest restartable scopes that read the changed value. Once you can see those scopes, recomposition stops being mysterious.
@Composable is a compiler plugin that adds hidden parameters to your function. Once you know what it adds, the rules about calling context, skipping and recomposition stop being arbitrary.
In Views you fix UI by reaching in and mutating it. Compose removes that ability entirely. Understanding why the removal is the feature is what makes the rest of Compose make sense.
