pub fn on_write(f: impl Fn() + Send + Sync + 'static)Expand description
Register what to do when a bound control writes.
Rust owns the state, so Rust decides when the interface is stale. The usual
implementation bumps a @State — see crate::state::set_state — which is
the one thing SwiftUI does track, and re-runs the body against whatever Rust
now holds. Without this, editing a Slider moves the thumb and updates the
Rust value while a Text showing that value stays as it was.
The first registration wins; later calls are ignored.