Please add a Default EventListener

[handstandsam]

When doing an initial setup/integration it's not easy to know that you need to create one of these and override the correct methods.

Finally figured out an issue after creating one of these and implementing some of the error and lifecycle (loaded, etc) methods.

EventListener: https://github.com/cashapp/redwood/blob/d3b544d528b07edef5afdb5300d33d301c2950ff/redwood-treehouse-host/src/commonMain/kotlin/app/cash/redwood/treehouse/EventListener.kt

[JakeWharton]

There is a default. Are you saying the behavior of the default should do something like log?

[handstandsam]

While hacking with @swankjesse to set up redwood on a new project, we had to provide our own EventListener in order to surface silent failures.

The event listener that we had to implement:

import app.cash.redwood.treehouse.EventListener
import app.cash.redwood.treehouse.TreehouseApp
import app.cash.zipline.Zipline
import app.cash.zipline.ZiplineManifest

class MyEventListener : EventListener() {

    override fun codeLoadStart(): Any? {
        println("codeLoadStart()")
        return null
    }

    override fun codeLoadSuccess(manifest: ZiplineManifest, zipline: Zipline, startValue: Any?) {
        println("codeLoadSuccess($manifest $zipline)")
    }

    override fun codeLoadSkipped(startValue: Any?) {
        println("codeLoadSkipped()")
    }

    override fun codeLoadSkippedNotFresh(startValue: Any?) {
        println("codeLoadSkippedNotFresh()")
    }

    override fun codeLoadFailed(exception: Exception, startValue: Any?) {
        println("codeLoadFailed($exception)")
    }

    override fun uncaughtException(exception: Throwable) {
        exception.printStackTrace()
    }

    class Factory : EventListener.Factory {
        override fun create(app: TreehouseApp<*>, manifestUrl: String?): EventListener {
            return MyEventListener()
        }
    }
}

Which we added here during treehouseAppFactory.create:

    private fun createTreehouseApp(httpClient: OkHttpClient): TreehouseApp<PathRoutableAppService> {
        val treehouseAppFactory = TreehouseAppFactory(
            context = applicationContext,
            httpClient = httpClient,
            manifestVerifier = ManifestVerifier.Companion.NO_SIGNATURE_CHECKS,
        )

        val manifestUrlFlow =
            flowOf("http://10.0.2.2:23368/manifest.zipline.json").withDevelopmentServerPush(
                    httpClient.asZiplineHttpClient()
                )

        val treehouseApp = treehouseAppFactory.create(
            appScope = scope,
            spec = object : TreehouseApp.Spec<PathRoutableAppService>() {
                override val name: String = "my"
                override val manifestUrl: Flow<String> = manifestUrlFlow
                override fun bindServices(zipline: Zipline) {
                    zipline.bind("RawTreehousePlatform", platform)
                }

                override fun create(zipline: Zipline): PathRoutableAppService {
                    return zipline.take("PathRoutableAppService")
                }
            },
            eventListenerFactory = MyEventListener.Factory()
        )

        treehouseApp.start()

        return treehouseApp
    }

Without that, all exceptions were silent and we were in the dark. It would have been nice to see the errors as it wasn't obvious to provide an event listener.

---

I'll DM you a link to the commit.