Error handling

ErrorEvents

This library provides a simple base events interface that is used in several places for error handling called ErrorEvents.

Here’s the whole implementation

interface ErrorEvents {
    fun onError(error: Throwable)
}

Some of the functionality requires that you implement this interface.

EventNotifier

Your ViewModels and other classes that can launch their own coroutines somehow have to communicate errors to the UI (or higher-level layers in general).

Note: This section only discusses the error-specific aspect of EventNotifier. See Event handling for more general usage of EventNotifier.

Imagine this in your business logic or ViewModel:

coroutineScope.launch {
    // someSuspendFun can throw an exception
    someSuspendFun()
}

If someSuspendFun() throws an exception, how will you let the user know that there is an error? You need an event queue/dispatcher that is processed by the UI. That’s what EventNotifier is.

val eventNotifier = EventNotifier<ErrorEvents>()

fun doSomething() {
    coroutineScope.launch {
        try {
            someSuspendFun()
        } catch (e: CancellationException) {
            throw e
        } catch (e: Throwable) {
            // This sends the event via eventNotifier
            eventNotifier { onError(e) }
        }
    }
}

You can simplify that code by using withErrorReporting:

val eventNotifier = EventNotifier<ErrorEvents>()

fun doSomething() {
    coroutineScope.launch {
        withErrorReporting(eventNotifier) {
            someSuspendFun()
        }
    }
}

BaseReactiveState

The multiplatform ViewModel base class BaseReactiveState already provides an eventNotifier and a launch function that catches exceptions:

class MyViewModel(scope: CoroutineScope) : BaseReactiveState<ErrorEvents>(scope) {
    init {
        launch {
            // ...code block...
        }
    }
}

This will automatically catch exceptions and trigger eventNotifier { onError(throwable) }.

See Multiplatform ViewModels for more details.