Crossfade

Crossfade — when an external Signal<K> changes, the previous content fades out while the new content fades in over the same window. Like Switcher, but animated.

let tab = Signal::new(Tab::Overview);
ctx.add(
    Crossfade::new(tab.clone(), |t| match t {
        Tab::Overview => Box::new(overview_panel()),
        Tab::Details  => Box::new(details_panel()),
    }),
);

Behavior

On each key change, both the previous-key widget and the current-key widget are rebuilt (via the supplied builder) and mounted side-by-side in a ZStack. The previous fades 1→0 while the current fades 0→1 over the configured duration. On the next key change, the previously-outgoing widget is torn down and the cycle repeats.

Builders should be cheap — they may run more than once per lifetime as the user navigates through several keys. For data- heavy panels, hoist expensive state out of the builder closure.

Reduced motion

Honours prefers-reduced-motion: snaps the opacity changes instead of tweening (instant swap).

Builder methods at a glance

duration

API reference

📖 Full rustdoc API for this module

pub struct Crossfade

Animated swap between widgets keyed by an external signal.

#![allow(unused)]
fn main() {
pub struct Crossfade<K: Eq + Clone + 'static> { /* fields */ }
}

Methods

pub fn new(key_signal: Signal<K>, builder: impl Fn(&K) -> Box<dyn Widget> + 'static) -> Self

New Crossfade driven by key_signal. The builder closure constructs the widget for a given key value. Builders can be invoked multiple times across the widget's lifetime as the user transitions through keys.

pub fn duration(mut self, duration: Duration) -> Self

Override the crossfade duration. Default: MotionTokens::duration_normal.