pub fn track(read: impl FnMut(), on_change: impl Fn() + Send + Sync + 'static)Expand description
Run read, remembering every observable property it touches, and call
on_change once when any of them next changes.
withObservationTracking, which is what SwiftUI itself uses to decide that a
view needs rebuilding. Once: the handler fires for the first change and
then the subscription is over, which is Swift’s behaviour too — a view
re-reads on the next render and so re-subscribes.