GUI for Akka application - swing

Question

I made a small application in Akka that has a hierarchy of actors (there is an ActorA that has several ActorB actors, and these ActorB actors have several ActorC actors). Now I'd like to add a small UI. This UI doesn't have any buttons, but just some labels that are modified when the ActorC actors receive certain messages from other actors. The problem that I have is that I must create a label for each ActorC actor, but the number (of ActorC actors) is not always the same, so I must create the ActorC actors in the first place, and then I must create the labels. I searched for tutorials on Scala Swing, but i just found old documentation or simple examples that are not useful in my case (something like press a button to do something). I even saw that several people used Java Swing in their Akka applications. I found a tool called Kamon, but i need to create an interface, not just monitoring my actors. Is there someone that can help me?

Answer 1

Swing is deprecated in favor of JavaFX. That said, JavaFX allows you to create a "rich client" application. It sounds like too heavy of a solution for what you want.
Perhaps a simple web UI? Have you looked at playframework.com? Your interface would just be some web pages that can talk to the actors. Play and Akka work well together, and it's pretty easy to get started with Play using available tutorials and templates.

Answer 2

There are two aspects to your design. The first aspect is the communication between your UI and your working actors. The second is the operation of your UI.
A scenario might be that your UI starts up and fires up a Swing EDT thread to display your status window. An actor is also created and it reaches out to your Actor A and says "ready to go". Actor A forwards the message to all Actor Bs, which forward it to the Actor Cs. Each Actor C then registers itself with the UI by sending a message "I am here" and "this is my status".
def receive = {
...
case ReadyToGo =>
myMonitor = sender
sender ! "ready"
}
The UI-Actor takes each of the registration messages and maps it to a label, creating it if needed. As each Actor C changes its state, it sends a new message to UI-Actor, saying "I am still here" and "this is my status".
The UI-Actor is the go-between the Akka world and the UI. This is the tricky part, since the UI-Actor runs on a different thread than the Swing event-dispatch-thread. It must put a task on the Swing queue for processing by the Swing thread in a thread-safe manner. Some rough code:
// assume labelMap is a map from ActorRef to Label, ordered by insertion
def receive = {
case IAmHere(status) =>
val actorC = sender
if ( ! (labelMap contains actorA) ) {
addStatusLabel(actorC, status)
}
case IAmStillHere(status) =>
updateStatusLabel(actorC, status)
}
def addStatusLabel(actorC: ActorRef, status: String) = {
Swing.onEDT {
labelMap(actorC) = new Label(status)
// recalculate the panel size
// repaint
}
}
def updateStatusLabel(actorC: ActorRef, status: String) = {
Swing.onEDT {
labelMap(actorC).text = status
// repaint
}
}
I leave it up to you to lay out the UI, the container, whether statuses are Strings or not, how to handle Actor Cs that go missing, etc.