On Mon, 3 Mar 2025 20:35:21 GMT, John Hendrikx <jhendr...@openjdk.org> wrote:
>> @hjohn could you help here please? How could we use Subscription in a >> situation when it has to be unsubscribed from within the lambda? > > I haven't been tracking these fixes for allowing initialization in background > threads, but it seems to me that basically anything should be allowed as long > as you're not part of a visible scene graph -- and I think there's also no > expectation that all functionality of a control "works" as long as it is not > yet part of such a graph (ie. the listeners are only needed once it is part > of a scene graph). > > If you make listeners conditional on being part of a scene graph, then I > think you can handle these with a single code path. Such a condition would > be: > > ObservableValue<Boolean> partOfSceneGraph = node.sceneProperty() > .flatMap(Scene::windowProperty) > .flatMap(Window::showingProperty) > .orElse(false); > > You can then safely install any listeners directly, regardless if they're on > a background thread or not: > > someProperty().when(partOfSceneGraph).subscribe( ... ); > > Or: > > someProperty().when(partOfSceneGraph).addListener( ... ); > > On a background thread, `partOfSceneGraph` will be `false`, and no listener > gets installed (yet). As soon as it becomes `true` all listeners with that > same condition become active. It becomes `true` automatically when the node > has a scene belonging to a window that is visible. Vice versa, if it ever > becomes `false` again, (which it may when the Node is removed or replaced) > all listeners using this condition are removed again. Thank you! This is not what I asked though: my question was about using `Subscription` in one-off case, and more specifically, about whether it is even possible to unsubscribe from within the lambda. What you are proposing is a slightly more involved change: for example, registering and unregistering listeners each time might introduce other issues (especially since we have no way to prioritize listeners/handlers). It also complicates the management of skin (as skins can be added/removed), something I would rather avoid. ------------- PR Review Comment: https://git.openjdk.org/jfx/pull/1697#discussion_r1978169002
