Observables in a remote interface are reactive streams of Event instances in Kotlin that, when connected to a Web Frame, can push data to the web layer. They are implemented with Asynchronous Flows, a powerful coroutine-based reactive programming library built by the Kotlin team , which means they are instances of Flows.

Observables can be declared any number of ways. The following examples are for a remote observable that sends events every time the network connection changes.

class Network {
    val visible = MutableSharedFlow<Event>()
}

val networkConnection = MutableSharedFlow<Event>()

For the following example, we’ll be using an observable declared like the following:

val networkConnection = MutableSharedFlow<Event>()

The observable reference can be passed directly to the Web Frame configuration.

Although you can add an instance of MutableSharedFlow directly to the Web Frame configuration, it is a good idea to convert it to an immutable flow first by using .asSharedFlow().

val configuration = WebFrame.Configuration(
    baseUrl = ...
    functions = ...
    observables = mapOf(
        "networkConnection$": networkConnection.asSharedFlow()
    ),
)

Remote observables must emit Event objects, which represent a single value sent to the web layer.

Create an Event object with arbitrary data.

Data must be JSON content on Android. One delightful way of creating arbitrary JSON content is by using the buildJsonObject helper from the KotlinX Serialization library:

val event = Event(buildJsonObject {
    put("type", "wifi")
})

Technically not a constructor, this function can be used to instantiate Event objects with any serializable object.

The easiest way to make a class serializable is by annotating it with @Serializable from the KotlinX Serialization library:

import kotlinx.serialization.*
import kotlinx.serialization.json.*

@Serializable
data class Connection(val type: String)

Then, objects can be passed to this constructor directly:

val event = Event(Connection("wifi"))

This constructor will throw an error if encoding fails (highly unlikely).