how awoid 2 times re render in react-native - reactjs

Question

i have tried to do routing according to user check and i did but my method worked two times. i understand it from my log
i'm using redux and here is my "useeffect" in mainrouter.js
// currentUser : null // in initialState for users
useEffect(() => {
if(states.currentUser== null)
{
console.log("Checking user for routing");
actions.getCurrentUserACT();
}
else{
console.log("Logged in")
}
},[]);
my mainrouter.js return
return (
<NavigationContainer>
{
states.currentUser == null ?
(this.SignStackScreen()) :
(this.MainTabNavigator())
}
</NavigationContainer>
);
here is my "getCurrentUserAct" method in redux actions
export function getCurrentUserACT() {
return function (dispatch) {
firebase.auth().onAuthStateChanged(user => {
if (user) {
console.log("User authed..");
dispatch({type:actionTypes.CURRENT_USER,payload:user})
} else {
console.log("User notauthed..");
dispatch({type:actionTypes.CURRENT_USER,payload:null})
}
});
}
when my app start, logs are .. (if i logged in before)
Checking user for routing
User authed
User authed
i think the reason for this, useeffect worked first time and state changed which use in return and rerender"
but then i removed to condition, logs were same.
so how i can avoid this?
is there a way to run method before from useeffect and avoid second render? or wait data in useeffect?

Answer 1

Your code looks right and there is no reason to log two times because of useEffect because you used it as componentDidMount so it is called one time.
The reason of logging two times is this code snippet:
firebase.auth().onAuthStateChanged(user => {
here onAuthStateChanged is callback and it is called when state of authentication changed on Firebase.
If you are going to check if the user logged in then you need to avoid to do like below
if (user) { }
Please try console.log(user) and check if user keeps same on double logging.
I believe user inner properties will be changed.
Hope this helps you to understand

Answer 2

export function getCurrentUserACT() {
return function (dispatch) {
firebase.auth().onAuthStateChanged(user => {
dispatch(setCurrentUserACT(user))
console.log("control point" + user);
// if (user) {
// console.log("User authed..");
// dispatch({type:actionTypes.CURRENT_USER,payload:user})
// } else {
// console.log("User notauthed..");
// dispatch({type:actionTypes.CURRENT_USER,payload:null})
// }
});
}
Logs were double
Checking user for routing
control point[object Object]
control point[object Object]
______________________Edited 31.05______________________
I change my code a little bit like below
const dispatch = useDispatch();
const currentUser = useSelector(state => state.currentUserReducer);
useEffect(() => {
console.log(JSON.stringify(currentUser));
if (currentUser == null) {
console.log("Checking user for routing");
//dispatch(getCurrentUserACT());
}
else {
console.log("Logged in")
}
}, []);
I found something like hint but I can't fix because i dont know
When app start logs are
null
Checking user for routing
I didnt dispatch getCurrentUserAct(), so logs are right. If i dispatch, user will be checking (user already logged in), component rerender and here is double logs from double render.
I need dispatch before useeffect, not in useeffect
Is there a way?