How to control scala swing listeners - swing

Question

This is a continuation to my last question. I used the MVC pattern with swing components and code goes like this
import scala.swing
import scala.swing.event._
case object MyBusinessEvent extends Event
class MyController extends Publisher {
val form = new MyForm
listenTo(form)
reactions += {
case MyBusinessEvent => //handle event code here
}
}
class MyForm extends Publisher {
val ui = new GridBagPanel {
val c = new Constraints
.... more code here
}
val button1 = new Button("Button 1")
//add button to panel
listenTo(button1)
reactions += {
case ButtonClicked(_) => publish(MyBusinessEvent)
}
}
However with multiple buttons the program hangs up and seems to stop publishing events. Is there any way to fix this? Thanks

Answer 1

Although from the truncated example it's not clear what the problem is, my guess is you are creating a cycle which unfortunately can happen quite easy with swing and MVC. that is, one model gets updated as part of listening to another model, and that again triggers an update in the other model. In java swing you have two choices,
a) temporarily remove the listener that is updating the model (e.g. do a removeActionListener before calling setSelectedItem on a JComboBox, and then afterwards re-register with addActionListener)
b) check for the event source (getSource on an java.util.EventObject) and ignore events in the model that originated from that very same model.
Now scala swing is more simplified, so you don't have event object and event sources. You can add though a source in your custom event case class. And it might be feasible to remove the reaction and re-add it after setting a model's state.

Answer 2

To avoid the cycles mentioned in 0__'s answer I have a trait like this:
trait Editable extends Publisher {
private var _editing = false
def editing = _editing
def editing_=(b: Boolean) = _editing = b
override def publish(e: Event) {
if(!editing) super.publish(e)
}
}
which I mix-in in the components I want to have more control about the events fired. So, when I want to change something without firing any event, I simply put the code between editing = true and editing = false.