user interface - Javafx concurrency and gui-update -

what i'm trying following: want fade in overlay screen before doing background work , fade overlay screen out when task finishes.

anyhow, java performs background task requestservice.dorequest , afterwards fades screen in , out. current order like:

• task
• fade in
• fade out

while should be:

• fade in
• task
• fade out

i think tried every possible configuration of threads, tasks, service, etc..

so how 1 correctly update gui try achieve?

controller.java:

public void dorequest(request r) {     task<float> t = new task<float>() {          @override         protected float call() throws exception {             try {                 updateprogress(.5f, 1);                 requestservice.dorequest(r);             } catch(exception e) {                 badge.setvisible(true);                 badge.settext(e.getmessage());             } {                 updateprogress(0f, 1);             }             return null;         }     };      overlay.opacityproperty().bind(t.progressproperty());     overlay.opacityproperty().addlistener((obs, o, n) -> system.out.println(n));     t.run();  } 

btw: if watch update of overlays opacityproperty, 1 can see property gets updated in right order, gui refresh seems hang.