Context update

[MFJoyBoy]

when i update the context value, other places that use context value won't update
please take look at the following link
https://github.com/MFJoyBoy/my-problems-with-leptos/tree/context-update

[MFJoyBoy]

can you tell what is the problem? please

[gbj]

    let current_user = RwSignal::new(CurrentUser { me: None });
    OnceResource::new_blocking(async move {
        let response = get_current_user_private_data().await;
        match response {
            Ok(value) => {
                current_user.update(|input| {
                    input.me = Some(value);
                });
            }
            Err(error) => {
                log!("{error:?}");
            }
        }
    });

You should not write to a signal inside the async block of a Resource, because during server rendering that async block will run on the server, but not on the client — so the value of current_user will not be set correctly on the client.

So, current_user always has me: None and then you click the button and set me to None again, which means it hasn't changed, which means the resource doesn't run again.

If you find yourself creating a resource (OnceResource in this case) and then immediately throwing it away, that's a pretty good sign that something has gone wrong.

You should probably either pass the resource itself through context, or wait for the value of the user via Suspense and pass that value through context.

[MFJoyBoy]

Screencast.From.2025-09-26.15-35-52.mp4

[MFJoyBoy]

i'm confused
so resource load the value on server, set it in initial html rendered on server and send it down to client, but on client the value is None
why page is not hydrated? (because None is None, it skip hydration?) i am not getting any error or warning either

[gbj]

During server rendering, the async block of a resource runs so that the value it returns can be serialized and sent to the client.

During initial hydration, the async block of a resource does not run. Instead, it deserializes the value that was sent from the server. If you think about it, this needs to be the case, because you do not want to unnecessarily repeat the work that was done on the server in the async block (which is usually something like fetching data from a database).

Your example does not use the value of the resource, which ran on the server and was serialized to the client. Instead, it runs a side-effect during the async block (setting the signal). This means that the value of the signal is only set on the server, but not on the client -- because that async block does not run during hydration on the client.

As a result, the me field has some value on the server, when the HTML is rendered, but the value is None on the client because the code that sets it to Some(_) is never run on the client.

The value of the resource on the client is correct, and is consistent with the value of the resource on the server — but you never read the value of the resource on either the client or the server. The value of the signal is inconsistent between them, because you are setting it in code that only runs on the server.

[MFJoyBoy]

okay, thanks a lot
with this function it works:

fn provide_current_user_context() {
    let current_user = RwSignal::new(CurrentUser { me: None });
    let resource_date = OnceResource::new_blocking(async move {
        let response = get_current_user_private_data().await;
        response
    });
    Effect::new(move || {
        spawn_local(async move {
            let response = resource_date.await;
            match response {
                Ok(value) => {
                    current_user.update(|input| {
                        input.me = Some(value);
                    });
                }
                Err(error) => {
                    log!("{error:?}");
                }
            }
        });
    });
    provide_context(current_user);
}