是否可以从 react-native 中的类组件访问功能上下文？

Question

I'm currently having react-native project v0.63.2 and using @react-navigation-5. Navigation from splash screen, login screen and tab screen is based from context.

appContext.js

import React from 'react';
const AppContext = React.createContext({IsLoading: true, IsLoggedIn: false});
export default AppContext;

navigationContainer.js

import AppContext from './appContext';
const StackApp = createStackNavigator();
export const StackNavigator = () => {
  const [appState, setAppState] = React.useState({});
  const state = { appState, setAppState };
  React.useEffect(() => {
    setAppState({ IsLoading: true, IsLoggedIn: false });
  }, []);

  return (
    <AppContext.Provider value={state}>
      {appState.IsLoading ? (
        <SplashScreen />
      )
        : (
          <NavigationContainer>
            <StackApp.Navigator>
              {
                appState.IsLoggedIn
                  ?
                  <>
                    <StackApp.Screen name='BottomTabScreen' component={BottomTabScreen} options={{ headerShown: false }} />
                  </>
                  :
                  <StackApp.Screen name='LoginScreen' component={NavigatorLogin} options={{ headerShown: false }} />
              }
            </StackApp.Navigator>
          </NavigationContainer>
        )}
    </AppContext.Provider>
  )
}

I recreate new login page with a class component. It can load all the previous way as functional component. But I unable to modify/update the context for IsLoggedIn: true .

What I have tried:- initLogin.js

import AppContext from '../navigator/appContext';
const AppState = ({ newContext }) => {
  const { setAppState } = React.useContext(AppContext);
  console.log('setAppState:=> ' + JSON.stringify(setAppState));
  console.log('newContext:=> ' + JSON.stringify(newContext));
  setAppState(newContext);
}
export class initSignIn extends Component {
   onPressLogin = () => {
      AppState({ IsLoggedIn: true });
   }
}

This will raise error hooks rules

Invalid hook call. Hooks can only be called inside of the body of a function component

I also tried use static context. No error but value undefined indicated the key IsLoggedIn is not there.

Some of my reference:

1. How to use React Context inside function of Class component
2. SO Answer

I added snack minimal script. Might having error due to UI Kitten theme I use. I'm not familiar with snack Minimal Script

Answer 1

This would be a working example that uses context with a class component. Remember that you can use only one context when you are accessing it from a class.

Here I have created a button component which would update the context. As you can see i have function inside the context which would update the context which we pass the setAppState function from useState.

  const AppContext = React.createContext({
      appState: { IsLoading: true, IsLoggedIn: false },
      setAppState: () => {},
    });
    
    export default function App() {
      const [appState, setAppState] = React.useState({
        IsLoading: false,
        IsLoggedIn: false,
      });
    
      return (
        <AppContext.Provider value={{ appState, setAppState }}>
          <View style={styles.container}>
            <Text style={styles.paragraph}>{JSON.stringify(appState)}</Text>
            <Button />
          </View>
        </AppContext.Provider>
      );
    }
    
    class Button extends React.PureComponent {
      render() {
        return (
          <TouchableOpacity
            onPress={() =>
              this.context.setAppState({
                IsLoading: !this.context.appState.IsLoading,
                IsLoggedIn: true,
              })
            }>
            <Text>Update</Text>
          </TouchableOpacity>
        );
      }
    }
    Button.contextType = AppContext;

Url for snack https://snack.expo.io/@guruparan/contextwithclass