Re: Coping with slow cons

Qs:
* How best to prevent blocking of EDT by slow GUI stuff?!
* How best to set and reset GUI cursor shapes?

In an ActionListener associated with a JMenuItem I had

     actionPerformed(actionEvent e) {
         switchPanel(new ComplexPanel());
     }

However ComplexPanel was taking a couple of seconds to build. During
this time the user is faced with an opened menu with an option selected
and nothing happening onscreen. This is undesirable!

This had me puzzled for a while. Since I'm used to moving non-GUI work
out of the EDT, it seemed like I needed to move some GUI work out of the
EDT! Catch 22. I decided to postpone it instead, so the
actionperformed() could return and the menu could then erase itself
immediately.

     actionPerformed(actionEvent e) {
         SwingUtilities.invokeLater(new Runnable() {
             public void run() {
                 switchPanel(new ComplexPanel());
             }
         });
     }

* Is this a normal idiom?

Anyway, the result is better but in order to let the user know the app
was busy I wanted to set an hourglass cursor

     actionPerformed(actionEvent e) {
         //final Cursor oldCursor = frame.getCursor();
         //frame.setCursor(new Cursor(Cursor.WAIT_CURSOR));
         SwingUtilities.invokeLater(new Runnable() {
             public void run() {
                 Cursor oldCursor = frame.getCursor();
                 frame.setCursor(new Cursor(Cursor.WAIT_CURSOR));
                 switchPanel(new ComplexPanel());
                 frame.setCursor(oldCursor);
             }
         });
     }

Originally I set the cursor ASAP, but I dislike having set and reset
separated in different methods so I changed it as shown. It seems OK

* Any gotchas I've missed?

One thing I'm not entirely happy with in a multithreaded application is
that some other thread might conceivably change the cursor after I've
stashed oldCursor. In which case restoring it might be inappropriate.
I'm pretty sure that my app wont do this (I'll disable other menu items
so that other threads can't be changing the cursor concurrently)

* Is there a better design for managing cursor state?