没有从函数[React Native]获得任何返回值

Question

I have this menu where I filter the button when user is logged and I'm accessing a function from a separate file to check out if user is logged or not.

From menu

import { IsLogged } from '../GlobalFunctions';

const SubDrawer1 = ({ data, onChange }) => (
    <View>
    {
        IsLogged() ? (
            <View>
                <TouchableOpacity onPress={()=>{onChange('LogoutScreen')}}>
                    <Text>Logout</Text>
                </TouchableOpacity>
            </View>
        ) : (<View />)
    }     
    </View>
);
export default SubDrawer1;

From GlobalFunctions

export function IsLogged(){
    AsyncStorage.getItem('userId').then((userId) => {
        return userId ? true : false
    })
}

From menu I call out IsLogged() function but the value is undefined when I console.log it. It supposed to return either true or false .

Answer 1

because AsyncStorage will take some time, and before that function completes its execution. (Because everything in JS is asynchronous)

So just make it wait until it finishes getting an item,

export function async IsLogged(){
    let userId = await AsyncStorage.getItem('userId');
    return userId ? true : false
}

Answer 2

You are trying to call a async function, so you need to add some extra code. Try the following.

SubDrawer1

import { Text, View, TouchableOpacity } from "react-native";

import React, { Component } from "react";
import { IsLogged } from "../GlobalFunctions";

const SubDrawer1 = async ({ data, onChange }) => {
  const status = await IsLogged();
  if (status === true) {
    return (
      <View>
        <View>
          <TouchableOpacity
            onPress={() => {
              onChange("LogoutScreen");
            }}
          >
            <Text>Logout</Text>
          </TouchableOpacity>
        </View>
      </View>
    );
  } else {
    return (
      <View>
        <View />
      </View>
    );
  }
};

export default SubDrawer1;

'IsLogged()' Global function

export function async IsLogged(){
    let userId = await AsyncStorage.getItem('userId');
    return userId ? true : false
}

'SubDrawer1' using class

...

import SubDrawer1 from "./SubDrawer1"; // import your 'SubDrawer1' component

var subDrawer1Component; // declare a variable for your rendering component

//Your main class
export default class ClassName extends Component<Props> {

  componentDidMount() {
    this.getComponentInfo(); //Call this method to get function
  }

  getComponentInfo = async () => {
    subDrawer1Component = await SubDrawer1();// Will take the component
    this.setState({ isDataGet: true });
  };

  render() {
    return (
        ...

        {subDrawer1Component}

        ...
    );
  }

}

...