如何使用 react hooks useEffect/useReducer + useContext 优雅地更改 ts 中上下文的值？

Question

As a React starter, I'm trying to achieve state management in my React app, and use useContext to share login status between components.

I started learning and read this question: >https://stackoverflow.com/questions/54738681/how-to-change-the-value-of-a-context-with-usecontext?r=SearchResults.

I tried what the answer told me -- use useEffect to update the context's value:

const initContext: GlobalContext = {
  login: false,
}

export const globalContext = React.createContext(null)

function App() { 

  return <globalContext.Provider value={useState(initContext)}>
    {useRoutes(router)}
  </globalContext.Provider>
}

But when I use ts to do the same thing, I got error

Type '[GlobalContext, Dispatch<SetStateAction>]' is not assignable to type 'null'.

So I tried another way:

const initContext: GlobalContext = {
  login: false,
}

export const globalContext = React.createContext(useState(initContext))

function App() { 
return <globalContext.Provider value={useState(initContext)}>
    {useRoutes(router)}
  </globalContext.Provider>
}

then I got another error:

React Hook "useState" cannot be called at the top level. React Hooks must be called in a React function component or a custom React Hook function.

or I've tried export const globalContext = React.createContext() , and got error Expected 1 arguments, but got 0.

So my question is how I can update the context's value in ts, could someone please help me?

Answer 1

You likely are wanting to provide a non-null default Context value. The useState hook also returns an array, not an object with a login boolean property. You want to pass an object with login as a property.

const initContext: GlobalContext = {
  login: false,
}

export const globalContext = React.createContext(initContext); // <-- pass initContext as default value

function App() {
  const [login, setLogin] = useState<boolean>(false);

  return (
    <globalContext.Provider value={{ login }}>
      {useRoutes(router)}
    </globalContext.Provider>
  );
}

Update

If you need to update the login value then the setLogin state updater should be passed in the Context value as well.

Example:

interface IGlobalContext {
  login: boolean;
  setLogin: React.Dispatch<React.SetStateAction<boolean>>;
}

const initContext: IGlobalContext = {
  login: false,
  setLogin: () => {}
};

const GlobalContext = React.createContext(initContext);

const useGlobalContext = () => React.useContext(GlobalContext);

function App() {
  const [login, setLogin] = useState<boolean>(false);

  return (
    <GlobalContext.Provider value={{ login, setLogin }}>
      {useRoutes(router)}
    </GlobalContext.Provider>
  );
}