Struct dioxus::prelude::Signal

pub struct Signal<T, S = UnsyncStorage>
where
    T: 'static,
    S: Storage<SignalData<T>>,
{ /* private fields */ }

Available on crate feature signals only.

Creates a new Signal. Signals are a Copy state management solution with automatic dependency tracking.

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

#[component]
fn App() -> Element {
    let mut count = use_signal(|| 0);

    // Because signals have automatic dependency tracking, if you never read them in a component, that component will not be re-rended when the signal is updated.
    // The app component will never be rerendered in this example.
    rsx! { Child { state: count } }
}

#[component]
fn Child(mut state: Signal<u32>) -> Element {
    use_future(move || async move {
        // Because the signal is a Copy type, we can use it in an async block without cloning it.
        state += 1;
    });

    rsx! {
        button {
            onclick: move |_| state += 1,
            "{state}"
        }
    }
}

Implementations

impl<T> Signal<T>

where T: 'static,

pub fn new(value: T) -> Signal<T>

Creates a new Signal. Signals are a Copy state management solution with automatic dependency tracking.

pub fn new_in_scope(value: T, owner: ScopeId) -> Signal<T>

Create a new signal with a custom owner scope. The signal will be dropped when the owner scope is dropped instead of the current scope.

pub const fn global(constructor: fn() -> T) -> GlobalSignal<T>

Creates a new global Signal that can be used in a global static.

impl<T> Signal<T>

where T: PartialEq + 'static,

pub const fn global_memo(constructor: fn() -> T) -> GlobalMemo<T>

Creates a new global Signal that can be used in a global static.

pub fn memo(f: impl FnMut() -> T + 'static) -> Memo<T>

Creates a new unsync Selector. The selector will be run immediately and whenever any signal it reads changes.

Selectors can be used to efficiently compute derived data from signals.

impl<T, S> Signal<T, S>

where T: 'static, S: Storage<SignalData<T>>,

pub fn new_maybe_sync(value: T) -> Signal<T, S>

Creates a new Signal. Signals are a Copy state management solution with automatic dependency tracking.

pub fn new_with_caller( value: T, caller: &'static Location<'static> ) -> Signal<T, S>

Creates a new Signal. Signals are a Copy state management solution with automatic dependency tracking.

pub fn new_maybe_sync_in_scope(value: T, owner: ScopeId) -> Signal<T, S>

Create a new signal with a custom owner scope. The signal will be dropped when the owner scope is dropped instead of the current scope.

pub fn manually_drop(&self) -> Option<T>

Drop the value out of the signal, invalidating the signal in the process.

pub fn origin_scope(&self) -> ScopeId

Get the scope the signal was created in.

pub fn id(&self) -> GenerationalBoxId

Get the generational id of the signal.

pub fn write_silent(&self) -> <S as AnyStorage>::Mut<'static, T>

👎Deprecated: This pattern is no longer recommended. Prefer peek or creating new signals instead.

This pattern is no longer recommended. Prefer peek or creating new signals instead.

This function is the equivalent of the write_silent method on use_ref.

What you should use instead

Reading and Writing to data in the same scope

Reading and writing to the same signal in the same scope will cause that scope to rerun forever:

let mut signal = use_signal(|| 0);
// This makes the scope rerun whenever we write to the signal
println!("{}", *signal.read());
// This will rerun the scope because we read the signal earlier in the same scope
*signal.write() += 1;

You may have used the write_silent method to avoid this infinite loop with use_ref like this:

let signal = use_signal(|| 0);
// This makes the scope rerun whenever we write to the signal
println!("{}", *signal.read());
// Write silent will not rerun any subscribers
*signal.write_silent() += 1;

Instead you can use the peek and write methods instead. The peek method will not subscribe to the current scope which will avoid an infinite loop if you are reading and writing to the same signal in the same scope.

let mut signal = use_signal(|| 0);
// Peek will read the value but not subscribe to the current scope
println!("{}", *signal.peek());
// Write will update any subscribers which does not include the current scope
*signal.write() += 1;

Reading and Writing to different data

Why is this pattern no longer recommended?

This pattern is no longer recommended because it is very easy to allow your state and UI to grow out of sync. write_silent globally opts out of automatic state updates which can be difficult to reason about.

Lets take a look at an example: main.rs:

fn app() -> Element {
    let signal = use_context_provider(|| Signal::new(0));
     
    // We want to log the value of the signal whenever the app component reruns
    println!("{}", *signal.read());
     
    rsx! {
        button {
            // If we don't want to rerun the app component when the button is clicked, we can use write_silent
            onclick: move |_| *signal.write_silent() += 1,
            "Increment"
        }
        Child {}
    }
}

child.rs:

fn Child() -> Element {
    let signal: Signal<i32> = use_context();
     
    // It is difficult to tell that changing the button to use write_silent in the main.rs file will cause UI to be out of sync in a completely different file
    rsx! {
        "{signal}"
    }
}

Instead peek locally opts out of automatic state updates explicitly for a specific read which is easier to reason about.

Here is the same example using peek: main.rs:

fn app() -> Element {
    let mut signal = use_context_provider(|| Signal::new(0));
     
    // We want to log the value of the signal whenever the app component reruns, but we don't want to rerun the app component when the signal is updated so we use peek instead of read
    println!("{}", *signal.peek());
     
    rsx! {
        button {
            // We can use write like normal and update the child component automatically
            onclick: move |_| *signal.write() += 1,
            "Increment"
        }
        Child {}
    }
}

child.rs:

fn Child() -> Element {
    let signal: Signal<i32> = use_context();
     
    rsx! {
        "{signal}"
    }
}

Trait Implementations

impl<T, S> Add<T> for Signal<T, S>

where T: Add<Output = T> + Copy + 'static, S: Storage<SignalData<T>>,

type Output = T

The resulting type after applying the + operator.

fn add(self, rhs: T) -> <Signal<T, S> as Add<T>>::Output

Performs the + operation.

impl<T, S> AddAssign<T> for Signal<T, S>

where T: Add<Output = T> + Copy + 'static, S: Storage<SignalData<T>>,

fn add_assign(&mut self, rhs: T)

Performs the += operation.

impl<T, S> Clone for Signal<T, S>

where T: 'static, S: Storage<SignalData<T>>,

fn clone(&self) -> Signal<T, S>

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T, S> Debug for Signal<T, S>

where T: Debug + 'static, S: Storage<SignalData<T>>,

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl<T, S> Default for Signal<T, S>

where T: Default + 'static, S: Storage<SignalData<T>>,

fn default() -> Signal<T, S>

Returns the “default value” for a type.

impl<T, S> Deref for Signal<T, S>

where T: Clone, S: Storage<SignalData<T>> + 'static,

Allow calling a signal with signal() syntax

Currently only limited to copy types, though could probably specialize for string/arc/rc

type Target = dyn Fn() -> T

The resulting type after dereferencing.

fn deref(&self) -> &<Signal<T, S> as Deref>::Target

Dereferences the value.

impl<T, S> Display for Signal<T, S>

where T: Display + 'static, S: Storage<SignalData<T>>,

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl<T, S> Div<T> for Signal<T, S>

where T: Div<Output = T> + Copy + 'static, S: Storage<SignalData<T>>,

type Output = T

The resulting type after applying the / operator.

fn div(self, rhs: T) -> <Signal<T, S> as Div<T>>::Output

Performs the / operation.

impl<T, S> DivAssign<T> for Signal<T, S>

where T: Div<Output = T> + Copy + 'static, S: Storage<SignalData<T>>,

fn div_assign(&mut self, rhs: T)

Performs the /= operation.

impl<T, S> From<Signal<T, S>> for ReadOnlySignal<T, S>

where T: 'static, S: Storage<SignalData<T>>,

fn from(inner: Signal<T, S>) -> ReadOnlySignal<T, S>

Converts to this type from the input type.

impl<T> IntoAttributeValue for Signal<T>

where T: Clone + IntoAttributeValue,

fn into_value(self) -> AttributeValue

Convert into an attribute value

impl<T> IntoDynNode for Signal<T>

where T: Clone + IntoDynNode,

fn into_dyn_node(self) -> DynamicNode

Consume this item along with a scopestate and produce a DynamicNode

impl<T, S> Mul<T> for Signal<T, S>

where T: Mul<Output = T> + Copy + 'static, S: Storage<SignalData<T>>,

type Output = T

The resulting type after applying the * operator.

fn mul(self, rhs: T) -> <Signal<T, S> as Mul<T>>::Output

Performs the * operation.

impl<T, S> MulAssign<T> for Signal<T, S>

where T: Mul<Output = T> + Copy + 'static, S: Storage<SignalData<T>>,

fn mul_assign(&mut self, rhs: T)

Performs the *= operation.

impl<T, S> PartialEq for Signal<T, S>

where T: 'static, S: Storage<SignalData<T>>,

fn eq(&self, other: &Signal<T, S>) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<T, S> Readable for Signal<T, S>

where S: Storage<SignalData<T>>,

fn peek_unchecked( &self ) -> <<Signal<T, S> as Readable>::Storage as AnyStorage>::Ref<'static, <Signal<T, S> as Readable>::Target>

Get the current value of the signal. Unlike read, this will not subscribe the current scope to the signal which can cause parts of your UI to not update.

If the signal has been dropped, this will panic.

type Target = T

The target type of the reference.

type Storage = S

The type of the storage this readable uses.

fn try_read_unchecked( &self ) -> Result<<<Signal<T, S> as Readable>::Storage as AnyStorage>::Ref<'static, <Signal<T, S> as Readable>::Target>, BorrowError>

Try to get a reference to the value without checking the lifetime. This will subscribe the current scope to the signal.

fn map<O>( self, f: impl Fn(&Self::Target) -> &O + 'static ) -> MappedSignal<O, Self::Storage>

where Self: Sized + Clone + 'static,

Map the readable type to a new type.

fn read(&self) -> <Self::Storage as AnyStorage>::Ref<'_, Self::Target>

Get the current value of the state. If this is a signal, this will subscribe the current scope to the signal. If the value has been dropped, this will panic. Calling this on a Signal is the same as using the signal() syntax to read and subscribe to its value

fn try_read( &self ) -> Result<<Self::Storage as AnyStorage>::Ref<'_, Self::Target>, BorrowError>

Try to get the current value of the state. If this is a signal, this will subscribe the current scope to the signal.

fn read_unchecked( &self ) -> <Self::Storage as AnyStorage>::Ref<'static, Self::Target>

Get a reference to the value without checking the lifetime. This will subscribe the current scope to the signal.

fn peek(&self) -> <Self::Storage as AnyStorage>::Ref<'_, Self::Target>

Get the current value of the state without subscribing to updates. If the value has been dropped, this will panic.

fn with<O>(&self, f: impl FnOnce(&Self::Target) -> O) -> O

Run a function with a reference to the value. If the value has been dropped, this will panic.

fn with_peek<O>(&self, f: impl FnOnce(&Self::Target) -> O) -> O

Run a function with a reference to the value. If the value has been dropped, this will panic.

fn index<I>( &self, index: I ) -> <Self::Storage as AnyStorage>::Ref<'_, <Self::Target as Index<I>>::Output>

where Self::Target: Index<I>,

Index into the inner value and return a reference to the result. If the value has been dropped or the index is invalid, this will panic.

impl<T, S> Sub<T> for Signal<T, S>

where T: Sub<Output = T> + Copy + 'static, S: Storage<SignalData<T>>,

type Output = T

The resulting type after applying the - operator.

fn sub(self, rhs: T) -> <Signal<T, S> as Sub<T>>::Output

Performs the - operation.

impl<T, S> SubAssign<T> for Signal<T, S>

where T: Sub<Output = T> + Copy + 'static, S: Storage<SignalData<T>>,

fn sub_assign(&mut self, rhs: T)

Performs the -= operation.

impl<T, S> Writable for Signal<T, S>

where T: 'static, S: Storage<SignalData<T>>,

type Mut<'a, R: 'static + ?Sized> = Write<'a, R, S>

The type of the reference.

fn map_mut<I, U, F>( ref_: <Signal<T, S> as Writable>::Mut<'_, I>, f: F ) -> <Signal<T, S> as Writable>::Mut<'_, U>

where U: 'static + ?Sized, F: FnOnce(&mut I) -> &mut U, I: ?Sized,

Map the reference to a new type.

fn try_map_mut<I, U, F>( ref_: <Signal<T, S> as Writable>::Mut<'_, I>, f: F ) -> Option<<Signal<T, S> as Writable>::Mut<'_, U>>

where I: 'static + ?Sized, U: 'static + ?Sized, F: FnOnce(&mut I) -> Option<&mut U>,

Try to map the reference to a new type.

fn downcast_lifetime_mut<'a, 'b, R>( mut_: <Signal<T, S> as Writable>::Mut<'a, R> ) -> <Signal<T, S> as Writable>::Mut<'b, R>

where 'a: 'b, R: 'static + ?Sized,

Downcast a mutable reference in a RefMut to a more specific lifetime

fn try_write_unchecked( &self ) -> Result<<Signal<T, S> as Writable>::Mut<'static, <Signal<T, S> as Readable>::Target>, BorrowMutError>

Try to get a mutable reference to the value without checking the lifetime. This will update any subscribers.

fn write(&mut self) -> Self::Mut<'_, Self::Target>

Get a mutable reference to the value. If the value has been dropped, this will panic.

fn try_write(&mut self) -> Result<Self::Mut<'_, Self::Target>, BorrowMutError>

Try to get a mutable reference to the value.

fn write_unchecked(&self) -> Self::Mut<'static, Self::Target>

Get a mutable reference to the value without checking the lifetime. This will update any subscribers.

fn with_mut<O>(&mut self, f: impl FnOnce(&mut Self::Target) -> O) -> O

Run a function with a mutable reference to the value. If the value has been dropped, this will panic.

fn index_mut<I>( &mut self, index: I ) -> Self::Mut<'_, <Self::Target as Index<I>>::Output>

where Self::Target: IndexMut<I>,

Index into the inner value and return a reference to the result.

impl<T, S> Copy for Signal<T, S>

where T: 'static, S: Storage<SignalData<T>>,

impl<T, S> Eq for Signal<T, S>

where T: 'static, S: Storage<SignalData<T>>,