dioxus/packages/signals/README.md

Dioxus Signals

Dioxus Signals is an ergonomic Copy runtime for data with local subscriptions.

Copy Data

All signals implement Copy, even if the inner value does not implement copy. This makes it easy to move any data into futures or children.

use dioxus::prelude::*;
use dioxus_signals::*;

#[component]
fn App(cx: Scope) -> Element {
    let signal = use_signal(cx, || "hello world".to_string());

    spawn(async move {
        // signal is Copy even though String is not copy
        print!("{signal}");
    });

    render! {
        "{signal}"
    }
}

Local Subscriptions

Signals will only subscribe to components when you read from the signal in that component. It will never subscribe to a component when reading data in a future or event handler.

use dioxus::prelude::*;
use dioxus_signals::*;

#[component]
fn App(cx: Scope) -> Element {
    // Because signal is never read in this component, this component will not rerun when the signal changes
    let signal = use_signal(cx, || 0);

    render! {
        button {
            onclick: move |_| {
                *signal.write() += 1;
            },
            "Increase"
        }
        for id in 0..10 {
            Child {
                signal: signal,
            }
        }
    }
}

#[derive(Props, Clone, PartialEq)]
struct ChildProps {
    signal: Signal<usize>,
}

#[component]
fn Child(cx: Scope<ChildProps>) -> Element {
    // This component does read from the signal, so when the signal changes it will rerun
    render! {
        "{cx.props.signal}"
    }
}

Because subscriptions happen when you read from (not create) the data, you can provide signals through the normal context API:

use dioxus::prelude::*;
use dioxus_signals::*;

#[component]
fn App(cx: Scope) -> Element {
    // Because signal is never read in this component, this component will not rerun when the signal changes
    use_context_provider(cx, || Signal::new(0));
    
    render! {
        Child {}
    }
}

#[component]
fn Child(cx: Scope) -> Element {
    let signal: Signal<i32> = *use_context(cx).unwrap();
    // This component does read from the signal, so when the signal changes it will rerun
    render! {
        "{signal}"
    }
}

Computed Data

In addition to local subscriptions in components, dioxus-signals provides a way to derive data with local subscriptions.

The use_selector hook will only rerun when any signals inside the hook change:

use dioxus::prelude::*;
use dioxus_signals::*;

#[component]
fn App(cx: Scope) -> Element {
    let signal = use_signal(cx, || 0);
    let doubled = use_selector(cx, || signal * 2);

    render! {
        button {
            onclick: move |_| *signal.write() += 1,
            "Increase"
        }
        Child {
            signal: signal
        }
    }
}

#[component]
fn Child(cx: Scope, signal: ReadOnlySignal<usize>) -> Element {
    render! {
        "{signal}"
    }
}