Getting AndroidRuntime: FATAL EXCEPTION: DefaultDispatcher-worker-1 with no other stack trace

Question

When using Retrofit and Coroutines to fetch data from an API I sometimes get an app crash with no stacktrace in Logcat except this: AndroidRuntime: FATAL EXCEPTION: DefaultDispatcher-worker-1

Answer 1

This is usually caused by Retrofit throwing a common exception like UnknownHostException (if there's no Internet) and coroutines swallowing the exception if you didn't specify a CoroutineExceptionHandler.

So add a coroutine exception handler in your launch code, something like this:

val coroutineExceptionHandler = CoroutineExceptionHandler{_, throwable ->
    throwable.printStackTrace()
}

fun getFromApi() {
    viewModelScope.launch(Dispatchers.IO + coroutineExceptionHandler) {
        retrofitService.getStuffFromInternet()
    }
}

Note this just logs the error to Logcat so you can see the missing stacktrace. You still need to figure out what's causing it.

Answer 2

I have encountered this type of error many times and what worked for me was to uninstall the app from the emulator and then installing it again.