JavaFX access controller's variables from Scene Builder - javafx-2

Question

If I declare something like
#FXML
private final static double PREF_SPACING = 10d;
or
#FXML
private Insets insets = new Insets(10d);
in the controller class,
is there a way to use their values in Scene Builder?
When I want to change the value, I want to change
it only once, in the controller class.

Answer 1

PRELIMINARY ANSWER
I haven't yet tried all of the techniques below, but it seems to be the way you would do it from reading the documentation. If I get some time, I'll try it out later and update this answer with results (or somebody else can do this and post a new answer or edit this one to create a definitive answer). I just wanted to publish something now to point you in what I believe to be the right direction.
If the below is not what you are looking for, add a few more specifics to your questions to fully describe what you want.
Don't using the #FXML annotation here. #FXML is for injecting values from the markup into the controller, not the other way around.
For your first example which is a constant, let's say your controller class is:
class MyControllerType {
public final static double PREF_SPACING = 10d;
}
Then in your fxml, reference the constant:
<?import MyControllerType?>
...
<VBox>
<spacing><MyControllerType fx:constant="PREF_SPACING"/></spacing>
</VBox>
For your second sample which is not a constant or a part of the SceneGraph, you can use an fx:define element to instantiate an instance of the class. Note that you can't directly instantiate an Insets class from FXML as it has no builder class nor zero length constructor. So what you might be able to do is create another placeholder class for the information and instantiate a reference to that in your FXML (or you can create a Builder that FXML can use to instantiate the Insets).
class InsetsHolder {
private Insets insets = new Insets(10d);
public Insets getInsets();
}
<?import InsetsHolder?>
<fx:define>
<InsetsHolder fx:id="i"/>
</fx:define>
<VBox>
<Button text="Click Me!" VBox.margin="$i.insets"/>
</VBox>
SceneBuilder should be able to read fxml files which use the fx:define and fx:constant notation, as well as (possibly) make use of the reference expression $i.insets. SceneBuilder might not have any UI to allow you to edit the values from within the SceneBuilder application, so you will probably need to hand edit the fxml file portions related to the fx:define and fx:constant elements if you wish to make use of these structures.
There is an executable example of using an fx:define element in this mailing list post on designing resolution independent units in FXML.
In general, I think I'd be a bit cautious of maintaining these kind of dependencies between fxml and java code. It may be more prudent to do more of this kind of stuff in plain Java code within the context of the controller initialize method as scottb suggests.

Answer 2

The #FXML annotation enables the JavaFX objects whose names you defined (fx:id) to have their references reflectively injected into nonpublic fields in the controller object as the scene graph is loaded from the fxml markup.
To the best of my knowledge, this is a one way operation. There is no provision for having named static class variables in the controller object injected into the scene graph during loading.
You can accomplish something very similar to what you are requesting by defining the values that you want set as class variables in your controller object's class, and then setting the appropriate object properties programmatically (rather than in markup) in the initialize() method of your controller object.
The initialize() method is called (if it is present) after the loading of the scene graph is complete (so all the GUI objects will have been instantiated) but before control has returned to your application's invoking code.