Thanks for your clarifications.
Maybe the actual problem is that we don't have a good name for "gets
the current value, but doesn't subscribe to updates".
We could call bindings "active" when changes of the source value are
processed, and "inactive" if the binding exists, but doesn't process
changes.
With a documented definition of "active", the method could simply be
named `activeWhen`.
On Mon, Nov 21, 2022 at 10:57 PM John Hendrikx <john.hendr...@gmail.com> wrote:
>
> Hi Michael,
>
> Thanks for your suggestion.
>
> The effect is not quite what you describe however, as the initial value
> when the operation is first invoked is retained. It's true however that
> when the condition is always `false` that the value will be a constant,
> and that when it is always `true` it effectively is just a duplicate of
> the left hand observable. Let me illustrate:
>
> public static void main(String[] args) {
> StringProperty sp = new SimpleStringProperty("foo");
> BooleanProperty active = new SimpleBooleanProperty(false); //
> inactive
> ObservableValue<String> x = sp.when(active); // holds "foo"
> despite being inactive
>
> System.out.println(x.getValue()); // prints "foo"
>
> sp.set("bar");
>
> System.out.println(x.getValue()); // still prints "foo"
>
> active.set(true);
>
> System.out.println(x.getValue()); // prints "bar"
> }
>
> This behavior doesn't violate the rule that the new binding shouldn't
> observe its source when the condition is false as no listener was
> involved to get the initial value. The initial value is important as
> all bindings must have some kind of value. The docs do describe this in
> the first sentence:
>
> "Returns an {@code ObservableValue} that holds this value and is updated
> only when {@code condition} holds {@code true}"
>
> I think `withScope` could work (or `scopedTo`) but not sure if "scope"
> itself is a good description -- we'd need to update the description to
> use the word scope in a way that makes clear what it does preferably
> without having to resort to "updated only when" or "only observes when":
> ie: "Returns an ObservableValue that is scoped to the given condition" ?
>
> --John
