How to react to getting focus from another application?

Question

My JavaFX 8 application has to doStuff() when it gets focused. That's pretty simple:

primaryStage.focusedProperty().addListener((observable, wasFocused, nowFocused) -> {
    doStuff();
});

However, when I display a dialog and user closes it, doStuff() fires. I want it to fire only when user switches from another app to mine, for example Alt+Tab from a browser.

In other words, I want to doStuff() iff other app's window loses focus and my app's window gets focus.

Is it possible?

Edit: Answers posted by FibreFoX and Appelemac require explicitly performing additional step before showing a dialog. This solution is far from perfect, because I (or any developer, in general) have to remember about this step before showing a dialog. Forgetting about it will introduce hard to find bugs.

Extending Dialog to do it automatically isn't an option, because I want to use built-in dialogs that already extend original Dialog.

That's pretty basic feature, I'd be surprised if there's no easy way to achieve this in JavaFX.

Answer 1

You could use a global boolean when opening such dialogs, and only when that global switch is true/false/whatever-you-choose then you could react on that state-switch.

public class GlobalDialogMemory{
    public static boolean dialogShown = false;
}

When using CDI you could inject the application-scoped current instance (but you should use getter/setter and non-static booleans instead ;)

Answer 2

I'd suggest adding a listener to your Dialog, which then allows you to not doStuff() if the Dialog was just closed/lost focus.

Easiest way I can think of is setting an Instant (with Instant.now) when the dialog is closed, and if the application regains focus, create another Instant, and check whether the Duration.between(instantLostFocusDialog, instantGainedFocusApp).getSeconds() exceeds 1 (or add getNano() to that to be more specific). Only then would you doStuff()