update global variable after reload the app

Question

I have defined a global variable in drawer component. I use this var in the same component and I change it, my approach works fine

import ....
...
const USERID_STORED = "userid_stored";
var userArray = [];
var lengthNow = 0;
...
class DrawerComponent extends React.Component {
  _goToMessages  = (route) => (
    () => {
      const navigateAction = NavigationActions.navigate({
        routeName: route
      });
      this.props.navigation.dispatch(navigateAction);
      this.props.navigation.closeDrawer();
      lengthNow = userArray.length; // change it here

    }

  );
...
render (
...
)
}

but whene I reload the App, lengthNow takes back his initial value 0

Can I let lengthNow keep its value ? how can I do it ?

if you have another aproach propose it to me please

hong developer · Accepted Answer · 2019-08-02 15:21:33Z

2

It is better to create, isolate, and manage global variables and functions separately.

const USERID_STORED = "userid_stored";
let userArray = [];
let lengthNow = 0;

function setUserArray(data) {
     userArray.push(data)
}

function getUserArray() {
     return userArray
}

function setlengthNow(data) {
     lengthNow = data
}

function getlengthNow() {
     return lengthNow
}

export {  USERID_STORED, userArray ,
        lengthNow,setUserArray, getUserArray,setlengthNow,getlengthNow }

Useage

import  {  USERID_STORED, userArray ,lengthNow,setUserArray, getUserArray,setlengthNow,getlengthNow } from "./globalfunction path"

....
setlengthNow(userArray.length) // change it here

If you do not want to lose the updated value, use AsyncStorage.

async componentDidmount() {
 const checkdata = await AsyncStorage.getItem("lengthNow");

 if(checkdata == null) {
    await AsyncStorage.setItem("lengthNow",userArray.length);
 }

}

answered Aug 2, 2019 at 15:21

hong developer

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2 Comments

zedArt Over a year ago

I think is the better way to do it thank you, but why I have to check if checkdata == null ?

hong developer Over a year ago

This is to make sure there is data when the app is reloaded.

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