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Comments (4)

Shmew avatar Shmew commented on May 29, 2024

This is due to the fact that the hub is a ref and thus only created once, so the value of count is always going to be 0.

This can be fixed like so:

let render = React.functionComponent(fun () ->
    let count,setCount = React.useState 0
    
    let countOne = React.useCallbackRef(fun () -> setCount (count + 1))

    let hub =
        React.useSignalR<Action,Response>(fun hub -> 
            hub.withUrl(Endpoints.Root)
                .withAutomaticReconnect()
                .configureLogging(LogLevel.Debug)
                .onMessage <|
                    function
                    | Response.NewCount _ -> countOne()
        )

I think in this situation it's probably better to just go ahead and wrap the entire function in the useCallbackRef hook:

let render = React.functionComponent(fun () ->
    let count,setCount = React.useState 0
    
    let handleMsg =
        React.useCallbackRef (fun msg -> 
            match msg with
            | Response.NewCount i -> setCount (count + 1)
        )

    let hub =
        React.useSignalR<Action,Response>(fun hub -> 
            hub.withUrl(Endpoints.Root)
                .withAutomaticReconnect()
                .configureLogging(LogLevel.Debug)
                .onMessage(handleMsg))

An alternative solution:

let render = React.functionComponent(fun () ->
    let count,setCount = React.useState 0
    
    let otherCount,setOtherCount = React.useState 0

    let hub =
        React.useSignalR<Action,Response>(fun hub -> 
            hub.withUrl(Endpoints.Root)
                .withAutomaticReconnect()
                .configureLogging(LogLevel.Debug)
                .onMessage <|
                    function
                    | Response.NewCount i -> setCount i
        )

    React.useEffect((fun () -> setOtherCount (count + 1)), [| count |])

I'm glad you brought this up, I should add this scenario to the documentation. Thanks!

from fable.signalr.

theimowski avatar theimowski commented on May 29, 2024

Thanks for explanation, I'll try that approach!

from fable.signalr.

mastoj avatar mastoj commented on May 29, 2024

Great example @Shmew , but how does the last one work?

from fable.signalr.

Shmew avatar Shmew commented on May 29, 2024

Whenever count is updated (via onMessage) the component will re-render, whenever the component re-renders and count has changed React will execute the function passed via useEffect setting otherCount. It's a bit convoluted, but demonstrates a way to fire additional side-effects after onMessage.

from fable.signalr.

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