Is my Stage visible ?

In my application, I often show some “popup window” for user’s input.

Quite often, I simply use JavaFX Alert class, and it does the trick :

Alert alert = new Alert(Alert.AlertType.WARNING);
alert.setHeaderText("Be careful");
alert.setContentText("I warned you");
alert.showAndWait();

But sometimes, I need to display more complex windows and I also want to remember where the user has left the window. For example, if the user has placed the search window in the upper-left corner. If he closes it and opens it again, maybe he would like to see it appear in the same spot.

That’s very convenient but I saw two problem occurring :

• The Window was displayed on a second monitor and the user has unplugged it. Now I’m trying to reapply values gathered from cache, and my window is obviously nowhere to be seen.
• The window was displayed, and it grows in height or width. Then, there’s a chance that the window will go out of screen, and will only be partially visible.

For these two cases, I made a very simple method that will compute whether my current window (Stage) is wrongly displayed :

    /**
     * Finds the screen where the Stage is and return true if some parts of the
     * stage are out of the screen, therefore not visible.
     *
     * @param stage
     * @return
     */
    public static boolean isStageOutOfBounds(Stage stage) {
        List<Screen> screenList = Screen.getScreensForRectangle(stage.getX(), stage.getY(), stage.getWidth(), stage.getHeight());
        /**
         * If the Stage is overlaping on several screens or not visible on any
         * screens, we assume we can't completly see it.
         */
        if (screenList.size() != 1) {
            return true;
        }
        Rectangle2D bounds = screenList.get(0).getVisualBounds();
        return stage.getX() < bounds.getMinX() 
                || stage.getX() + stage.getWidth() > bounds.getMaxX()
                || stage.getY() < bounds.getMinY() 
                || stage.getY() + stage.getHeight() > bounds.getMaxY();
    }

Then, I only need to make the verification, and call the appropriate :

stage.centerOnScreen();

if necessary.