setState React Context not working in next.js

Question

I'm working with nextjs and I want to try the React Context for a global variable, everything seems to be well added but the function for updating the Global Variable is not working, after spending the whole day reading and following documentation and blogs and stackoverflow I can't find any solution or where the problem is.

here is my code:

Provider.tsx:

import React, { createContext, useCallback, useState } from 'react'

export interface ITodo {
  id: number
  title: string
  description: string
  status: boolean
}
export type TodoContextTypeTEST = {
  todos: ITodo[]
  saveTodo: (todo: ITodo) => void
}

type Props = {
  children: React.ReactNode
}

export const TodoContext = createContext<TodoContextTypeTEST>({ saveTodo: () => {}, todos: [] })

const TodoProvider: React.FC<Props> = ({ children }) => {
  const [todos, setTodos] = useState<ITodo[]>([])


  const saveTodo = useCallback(
    (newTodo: ITodo) => {
      console.log('here in the provider', newTodo)
      setTodos([...todos, newTodo])
      console.log('after save in the provider', todos)
    },
    [todos],
  )

  return <TodoContext.Provider value={{ todos, saveTodo }}>{children}</TodoContext.Provider>
}

export default TodoProvider

_app.tsx (wrapping the provider globally):

<TodoProvider>
      <QueryClientProvider client={queryClient}>
        <GlobalStyle />
        <Layout>
          <Component {...pageProps} />
        </Layout>
        <ReactQueryDevtools initialIsOpen={false} />
      </QueryClientProvider>
    </TodoProvider>

Then inside of a form after the submit I added the save method:

const { saveTodo } = useContext(TodoContext) as TodoContextTypeTEST

and I call it with the data I want to update:

saveTodo({ id: 3, title: 'post 3', description: 'this is a description 3',status: false})

Then I check in another component and the data is not update:

const { todos } = useContext(TodoContext)

Joe · Accepted Answer · 2022-08-30 00:12:16Z

2

I found that my issue was to do with setState not firing any re-render by only mutating an object value in an array.

Instead of:

const setQuantity = (productId: string, quantity: number) => {
  let index = items.findIndex((item) => item.product.id == productId)
  items[index].quantity = quantity
  setItems(items)
}

I need to recreate the array like so:

const setQuantity = (productId: string, quantity: number) => {
  let index = items.findIndex((item) => item.product.id == productId)
  items[index].quantity = quantity
  setItems([...items])
}

answered Aug 30, 2022 at 0:12

Joe

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Comments

Buggies · Accepted Answer · 2022-07-11 15:42:19Z

1

I think the problem can be with context value - it is recreated.

I looked at my code and docs and everywhere is used state as context value.

Try this:

const TodoProvider: React.FC<Props> = ({ children }) => {
  const [todos, setTodos] = useState<ITodo[]>([])

  const saveTodo = useCallback(
    (newTodo: ITodo) => {
      setTodos((oldTodos) => [...oldTodos, newTodo])
    },
    [setTodos],
  )

  const [contextValue, setContextValue] => useState({ todos, saveTodo })

  useEffect(() => { setContextValue({ todos, saveTodo }) }, [todos, saveTodo])

  return <TodoContext.Provider value={contextValue}>{children}</TodoContext.Provider>
}

then in component try this:

return (
  <TodoContext.Consumer>{({ todos }) => ( render something )}</TodoContext.Consumer>
)

edited Jul 11, 2022 at 15:42

answered Jul 8, 2022 at 19:56

Buggies

3831 silver badge7 bronze badges

7 Comments

DevDuke Over a year ago

Hello @Buggies thanks for your response, I've tried your code in codesandbox and works ! codesandbox.io/s/wonderful-chebyshev-6wx8sb but in my Nextjs App it doesn't it is driving me crazy, I can't find what's the error, maybe is for the server side rendering...I don't know I don't find anything related it.

Buggies Over a year ago

@DevDuke I have it in nextJS app too so it should work, try use it like I updated the response. Thats only difference I can see.

DevDuke Over a year ago

thanks for your help, still doesn't work, I can see that I can update the array but when I go to the component where I need the context array of todos, is completely empty, is like reset or just take the initial values not the update values, I tried your updated response: <TodoContext.Consumer> {({ todos }) => todos.map((x: any) => <div key={x.id}>title: {x.title}</div>)} </TodoContext.Consumer>

Buggies Over a year ago

and are you logging the todos in your provider if they really changed?

Buggies Over a year ago

Last try I changed dependencies in useCallback and useEffect. Last chance is that you share your repo so I can try it

|

DevDuke · Accepted Answer · 2022-07-11 15:48:18Z

0

Final I crossed with the final solution, it was all about the next/link, you can find the right answer here React Context not updating value to pass to another page . I wasn't using the next/link to navigate to the updated component.

answered Jul 11, 2022 at 15:48

DevDuke

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