---
description: Screen UI contract structure for State, Action, and Event
alwaysApply: false
---
# Screen UI Contract Rule

Every screen must define its contract in a `*ScreenContract.kt` file using `State`, `Action`, and `Event`.

## Required structure

1. Define `State` with all static UI data required to render the screen.
2. Define `Action` (enum or sealed interface) for what the ViewModel does.
3. Define `Event` (enum or sealed interface) for user interactions.

## State guidelines

- `State` must include stable screen data (for example `deviceName`, `deviceId`, `isSharingEnabled`).
- Do not put user interaction triggers in `State`; those belong to `Event`.

## Action guidelines

- Use `Action` for ViewModel-driven outcomes such as navigation or side effects.
- Example: `Action.NavigateTo*Screen`, `Action.Show*Toast`

## Event guidelines

- Use `Event` for user-originated input.
- Examples: `Event.*ButtonClicked`, `Event.*InputChanged(value)`.

## Example

```kotlin
data class State(val deviceName: String, val deviceId: String, val isSharingEnabled: Boolean)

sealed interface Action { data object NavigateToScreenX : Action }

sealed interface Event {
    data object XButtonClicked : Event
    data class InputChanged(val value: String) : Event
}
```