Question

I’m writing a 2D polygon and physics editor, one functionality is to set a rotation limit for joints.

To use this functionality, the user clicks and drags a line between the joint points which need to receive the limit.

The logic of determining if the pick is valid happens outside of the GUI code.

If a pick is found, I wanted to pop up a JOptionPane.showInputDialog where the user can input the limit.

Thing is, if I do it directly, the program becomes unresponsive, I figure it’s because of threading.

I’s there a way to define an event listener the GUI can use that doesn’t require an actual GUI component?

I want to send an event that also contains a reference to the target object to that component, then telling it that a valid pick has been made and user input is required, and then send the value back via a method of the target object.

I am very inexperienced with Swing.
My hunch is that I might be able to add an ActionListener to the main window, but I don’t know how I could address that listener specifically.
As in, how would I need to define an Action that only gets processed by that particular listener?
If that is actually possible, of course.

So far I have only used listeners to let the GUI talk to the logic, not the other way around…

Edit:
The program becomes unresponsive the movement I call
result = JOptionPane.showInputDialog(this,"Enter Limit.");

That just breaks it. Can’t even enter anything into the textbox, nor close it, etc.

I figure it’s because it spawns a modal dialog that pauses some thread, and calling it from somewhere in the bowels of non GUI code is just not the thing I should do, but I’m too inexperienced to know another way…

Edit2:
I should add that I can use JOptionPane.showInputDialog without any problems if I spawn it, for example, after clicking a button or choosing a popup menu option.
In fact that’s how I rename the items I am working with.

But I assume at that point, the dialog is being spawned inside the GUI thread, or this Event Dispatcher queue thing.

The problem with this though is, that this takes visible, interactive GUI components that fire that event.
What I’d like, however, is some sort of component that would spawn JOptionPane.showInputDialog just like a clicked button or context menu would, but without having to be interacted with by the user, but instead by the code.
I guess I could use invisible buttons and emulate mouseclick events, but that’s pretty hacky…

Also, I tried spawning Threads and Runnables which spawned the JOptionPane.showInputDialog, but that didn’t help either.
Unless I spawn the JOptionPane from a GUI source, everything stalls, and the dialog won’t work.

Answer 1

It should be possible for your background thread to spawn a dialog with invokeAndWait():

final double[] result = new double[1];
SwingUtilities.invokeAndWait(new Runnable() {
   public void run() {
      try {
         result[0] = Double.parseDouble(
            JOptionPane.showInputDialog("Enter value:"));
      } catch(NumberFormatException e) { 
         result[0] = -1;
      }
   }
}
// ... do something with result[0]

Here I made the result an array just so that it can be final (accessible to the anonymous class) and also mutable.