`Action`s represent payloads of information that send data from your application to the `Store`. You can send actions using `store.dispatch()`. An `Action` will usually be a small data class or object describing a change.
They take the previous state and an action as parameters, and return the new state as a result of that action.
```Kotlin
fun reduce(previousState: State, action: Action) = when (action) {
is SetVisibility -> previousState.copy(toolbarVisible = action.visible)
else -> previousState
}
```
### Store
The `Store` brings together actions and reducers. It holds the application state and allows access to it via the `store.state` getter. It allows state to be updated via `store.dispatch()`, and can have listeners registered through `store.observe()`.
Stores can easily be created if you have a reducer.
```Kotlin
val store = Store<State,Action>(
initialState = State(),
reducer = ::reduce
)
```
Once the store is created, you can react to changes in the state by registering an observer.
```Kotlin
store.observe(lifecycleOwner) { state ->
toolbarView.visibility = if (state.toolbarVisible) View.VISIBLE else View.GONE
}
```
`store.observe` is lifecycle aware and will automatically unregister when the lifecycle owner (such as an `Activity` or `Fragment`) is destroyed. Instead of a `LifecycleOwner`, a `View` can be supplied instead.
If you wish to manually control the observer subscription, you can use the `store.observeManually` function. `observeManually` returns a `Subscription` class which has an `unsubscribe` method. Calling `unsubscribe` removes the observer.
## License
This Source Code Form is subject to the terms of the Mozilla Public
License, v. 2.0. If a copy of the MPL was not distributed with this
file, You can obtain one at http://mozilla.org/MPL/2.0/
