Is there any way i can get the current Display object from a background thread(jobs) in RAP

Question

we need to get the the current display object in RAP 2.3 from inside a job for updating the UI. what is the suggested way to do that?

Answer 1

The Threads in RAP articles gives a thorough explanation about how threads and sessions interrelate in RAP.

To gain access to the Display from a Job, the Job needs to know which Display it is assigned to. Hence you need to pass the Displya to the Job. If the Job is scheduled from the UI thread, typical code may look like this:

  static class DisplayJob extends Job {
    private final Display display;

    private DisplayJob( Display display ) {
      super( "Job with UI Access" );
      this.display = display;
    }

    @Override
    protected IStatus run( IProgressMonitor monitor ) {
      display.asyncExec( new Runnable() {
        @Override
        public void run() {
        }
      } );
      return Status.OK_STATUS;
    }
  }


  Button button = new Button( ...
  button.addListener( SWT.Selection, new Listener() {
    @Override
    public void handleEvent( Event event ) {
      new DisplayJob( event.display ).schedule();;
    }
} );

Don't forget to check if the widgets aren't disposed before accessing them in the run() method given to asyncExec() - or use a helper therefore.

Note that the thread/session relation isn't specific to RAP but applies to all multi-user environments that have the concept of a session.