Binding Question

Question

Ok, I'm slowly, slowly starting to get my tiny little brain around the binding API.
I've worked out the following bit of code to 'or' together a bunch of boolean values:
BooleanProperty parent = new SimpleBooleanProperty();
BooleanProperty child1 = new SimpleBooleanProperty();
BooleanProperty child2 = new SimpleBooleanProperty();
BooleanProperty child3 = new SimpleBooleanProperty();
parent.bind(child1.or(child2).or(child3));
System.out.println(String.format("0) Parent=%s (child1=%s, child2=%s, child3=%s)",
        parent.get(), child1.get(), child2.get(), child3.get()));
child1.set(true);
System.out.println(String.format("0) Parent=%s (child1=%s, child2=%s, child3=%s)",
        parent.get(), child1.get(), child2.get(), child3.get()));Seems obvious now but originally I spent a lot of time working out why this wouldn't work (I guess I was thinking that since the '.bind' method was like an 'equals', the '.or' method was similar):
// don't do this at home
parent.or(child1);
parent.or(child2);
parent.or(child3);My problem now is that I don't know my variables up front. Imagine I've got a class that gets boolean values passed to it to bind to, how do I progressively bind to it in a nice way? Do I need to keep track of the BooleanBinding instance and add to this?
The best I've come up with for doing this is the following, but this seems horribly complex for what I want to do and I reckon (hoping) I'm missing something. Can anyone streamline the following at all?
public class MyClass
    private BooleanProperty parent;
    private BooleanProperty first;
    private BooleanBinding binding;
    public MyClass()
        parent = new SimpleBooleanProperty();
    public void trackThisGuy(BooleanProperty child)
        if (first == null)
            // first guy we have to bind directly
            parent.bind(child);
            first = child;
        else if (booleanBinding == null)
            // second guy we have to create our binding with the first guy
            booleanBinding = first.or( child );
            parent.bind(booleanBinding);     
        else
            // everyone else we add to our binding and rebind
            booleanBinding = booleanBinding.or(child);
            parent.bind(booleanBinding);
}I feel like I should be able to replace that whole mess of if-else statements with a single line of something like parent.or(child) but, as we found out above, that doesn't work.
Currently I'm just holding onto the BooleanProperty's passed in and then recreating the whole binding each time but this is not nice either.
Cheers for the help,
zonski

Answer 1

Hi Michael,
I have a few scenarios where I have hit this issue.
One example is the 'glasspane' example I have mentioned in a few posts earlier. In this, I have a top-level StackPane with a 'glasspane' in it that blocks the dialog (by preventing input and showing a loading cursor) whenever one of the child controllers is 'busy' (i.e. it is running a background thread).
The child controllers get added and removed dynamically on a regular basis. So I'd like to be able to have a method to do something like:
public void registerBusyWorker(BusyWorker child)
    glassPane.visibileProperty().orWithCurrentBinding(child.busyPoperty());
public void removeBusyWorker(BusyWorker child)
    glassPane.visibileProperty().removeFromCurrentBinding(child.busyPoperty());
} I've just used those method names to be explicit about what I am trying to do, I'm not suggesting they would be good names.
Of course I could implement this with the low level API and I could do it the old fashion way and roll my own event handlers, etc. I was just expecting the high level binding to give me something nice in this space. It could be that my case falls outside the 80-20 rule and it may not be worth catering for, but I've certainly hit it. Maybe my expectations of the API have been influenced by the Hibernate Criteria API too (http://docs.jboss.org/hibernate/core/3.3/reference/en/html/querycriteria.html) which has similar Java based 'expressions' but a totally different way of doing it.
If I implemented it using the low-level binding API I believe it would look like this:
private List<BusyWorker> busyWorkers = new ArrayList<BusyWorker>();
public void registerBusyWorker(BusyWorker child)
    busyWorkers.add(child);
    child.busyProperty().addListener(this);
    updateState();
public void removeBusyWorker(BusyWorker child)
    busyWorkers.remove(child);
    child.busyProperty().removeListener(this);
    updateState();
public void changed(ObservableValue<? extends Boolean> source, Boolean oldValue, Boolean newValue)
    updateState();
protected void updateState()
    for (BusyWorker : busyWorkers)
        if (busyWorker.isBusy())
            glassPane.setVisible(true);
            return;
    glassPane.setVisible(false);
}