Android Kotlin handling exceptions on ui thread with anko doAsync

Question

I am new to Kotlin and I have this doAsync with a custom exception handler:

doAsync(exceptionHander = {e -> handleException(e)}){
     //rest call
}

 private val handleException= {throwable : Throwable ->
        if(throwable is HttpClientErrorException){
            val response = JSONObject(throwable.responseBodyAsString)
            Toast.makeText(this, response["message"].toString(), Toast.LENGTH_LONG).show()
        }
    }

However the Toast is never shown. How can I show this exception message on a Toast? Is the exception handler called on the ui thread?

Update:

I have tested this way:

doAsync(exceptionHander = {e -> handleException(e)}){
      throw HttpClientErrorException(HttpStatus.INTERNAL_SERVER_ERROR, "An error has occurred")
}

with the same error handler, however the toast won't show.

Answer 1

Since the exception handler is called in a background thread, I used a try-catch in the doAsync bloc.

doAsync{
     var exception: Exception? = null
     try {
          //rest call
     }
     catch(e: HttpClientErrorException){
          exception = e
     }
     uiThread {
        if (exception != null){
             // Show the exception message. 
        }
        else {
             // Update the UI with the result
        }
     }
}

So this way one can handle the expected exception on the UI thread. Feedback is welcome.