How to interrupt the window closing mechanism in scala swing

Question

I'm building a GUI with the SimpleSwingApplication trait in scala swing. What I want to do is to provide a mechanism on close, that asks the user (Yes,No,Cancel) if he didn't save the document yet. If the user hits Cancel the Application shouldn't close. But everything I tried so far with MainFrame.close and closeOperation didn't work.

So how is this done in Scala Swing?

I'm on Scala 2.9.

Thanks in advance.

Answer 1

Slightly different variation from what Howard suggested

import scala.swing._

object GUI extends SimpleGUIApplication {
  def top = new Frame {
    title="Test"

    import javax.swing.WindowConstants.DO_NOTHING_ON_CLOSE
    peer.setDefaultCloseOperation(DO_NOTHING_ON_CLOSE)

    override def closeOperation() { showCloseDialog() }

    private def showCloseDialog() {
      Dialog.showConfirmation(parent = null,
        title = "Exit",
        message = "Are you sure you want to quit?"
      ) match {
        case Dialog.Result.Ok => exit(0)
        case _ => ()
      }
    }
  }
}

By using DO_NOTHING_ON_CLOSE you are given a chance to define what should be done when a WindowEvent.WINDOW_CLOSING event is received by the scala frame. When a scala frame receives a WINDOW_CLOSING event it reacts by calling closeOperation. Hence, to display a dialog when the user attempts to close the frame it is enough to override closeOperation and implement the desired behavior.

Answer 2

What about this:

import swing._
import Dialog._

object Test extends SimpleSwingApplication { 
  def top = new MainFrame { 
    contents = new Button("Hi")

    override def closeOperation { 
      visible = true
      if(showConfirmation(message = "exit?") == Result.Ok) super.closeOperation  
    }
  }
}