Im working with my friends on a app project and we find an issue many times when we tring to set a use state and the console log the variable, i've looking for a solution in the website and saw that the reason is that the usestate is an async awiat which means the variable that i set in the use state isn't immidatly set in it, so i tried many solution that i found in the websites but none of them work for me.
in the screenShot you can see that the json variable is in console log before and the set varaible doesn't show after the setActiveUser , any help?
Thanks!
If you want to do something upon setting state then your best bet is to use the useEffect hook from React and adding your state in the dependency array. This will then call the function in your useEffect every time the state changes. See below a rough example:
import { Text } from 'react-native';
const MyComponent = () => {
const [activeUser, setActiveUser] = useState(null);
useEffect(() => {
// This should log every time activeUser changes
console.log({ activeUser });
}, [activeUser]);
const fetchAuthentication = async user => {
var flag = false;
await fetch('/api/authUser/', {
method: 'PUT',
headers: { 'Content-Type': 'application/json' },
body: JSON.stringify(user),
})
.then(res => {
res.ok && (flag = true);
return res.json();
})
.then(json => {
if (flag) {
setActiveUser(json);
}
})
.catch(error => console.error(error));
return flag;
};
return <Text>Hi</Text>;
};
Full documentation: https://reactjs.org/docs/hooks-effect.html
Related
I am modifying a state variable (setTokens(tokens - 1)) in React native and then using the modified variable in an axios PUT request (library_tokens: tokens).
The problem is, the put request is successful, but it puts the old value of the variable instead of the modified one in the database after the PUT request.
The following is the code:
const [tokens,setTokens] = useState(0)
const lendBook = book => {
// Add book to the IssueReturn collection in the database
issuesApi
.post('/bookissue', {
booksIssued: book._id,
image: book.image,
user: context.stateUser.user.userId,
})
.then(response => {
if (response.status === 200) {
// Decrement user's library token
setTokens(tokens - 1);
// Modify the user's library tokens
userProfileApi
.put(
`/${context.stateUser.user.userId}`,
{
library_tokens: tokens,
},
{
headers: {Authorization: `Bearer ${jwtToken}`},
},
)
.then(response => {
console.log('tokens', tokens);
});
}
})
.catch(err => {
console.log(err);
});
};
You can use useEffect like this.
useEffect(() => {
console.log(tokens) // do something after state has updated
}, [tokens])
After state updation the useEffect will be called, so you can call userProfileApi inside useEffect.
setTokens it not a synchron function. code executed afterwards will not have the updated state. either use a local variable to store the result of token - 1 or make use of the useEffect hook.
When kept in the component body, the following code works fine. Inside useEffect, it checks the asyncstorage and dispatches an action (the function is longer but other checks/dispatches in the function are of the same kind - check asyncstorage and if value exists, dispatch an action)
useEffect(() => {
const getSettings = async () => {
const aSet = await AsyncStorage.getItem('aSet');
if (aSet) {
dispatch(setASet(true));
}
};
getSettings();
}, [dispatch]);
I'm trying to move it to a custom hook but am having problems. The custom hook is:
const useGetUserSettings = () => {
const dispatch = useDispatch();
useEffect(() => {
const getSettings = async () => {
const aSet = await AsyncStorage.getItem('aSet');
if (aSet) {
dispatch(setASet(true));
}
};
getSettings();
}, [dispatch]);
};
export default useGetUserSettings;
Then in the component where I want to call the above, I do:
import useGetUserSettings from './hooks/useGetUserSettings';
...
const getUserSettings = useGetUserSettings();
...
useEffect(() => {
getUserSettings();
}, [getUserSettings])
It returns an error:
getUserSettings is not a function. (In 'getUserSettings()', 'getUserSettings' is undefined
I've been reading rules of hooks and browsing examples on the internet but I can get it working. I've got ESlint set up so it'd show if there were an invalid path to the hook.
Try the following.
useEffect(() => {
if (!getUserSettings) return;
getUserSettings();
}, [getUserSettings]);
The hook doesn't return anything, so it's not surprising that the return value is undefined ;)
I am using an api call to get information for my app which I display to the user. The problem is that when I open the screen for the first time the app displays the information but when I go to a different screen and then comeback I dont see the information unless I restart the app.
This function makes the apiCall for me:
async function getOrders() {
var retrieveData = async () => {
try {
var value = await AsyncStorage.getItem("user");
var data = JSON.parse(value);
return data.user.email;
} catch (error) {
alert(error);
}
};
retrieveData().then((usr) => {
setUser(usr)
fetch(URL + "/api/order/quoted", {
method: "POST",
body: "user=" + usr,
headers: { "Content-type": "application/x-www-form-urlencoded" },
})
.then((response) => response.json())
.then((responseJson) => {
if (responseJson.error === null) {
setOrders(responseJson.orders);
}
});
});
}
First I use the retriveData function to get the used id, based on that information is server to the user.
You are using react-navigation version 5, so you need to wrap your logic fetch data in useFocusEffect hook react navigation docs
import { useFocusEffect } from '#react-navigation/native';
useFocusEffect(
React.useCallback(() => {
getOrders()
}, [getOrders])
);
The problem can be solved in the following steps:
If you want the data fetched from your endpoint to be used even if you move to other screen use Redux.
If you use redux or not and want to fetch the api every time you open a specific screen then you need to add an onfocus listener. An example is here https://reactnavigation.org/docs/navigation-events/
class Profile extends React.Component {
componentDidMount() {
this._unsubscribe = navigation.addListener('focus', () => {
// do something
});
}
I am trying to build an app in react native that is suppose to take take two inputs by a user and then make a query to an api and get information about the two inputs. I have been having trouble with redux and redux-thunk and specifically with async actions.
This is the code in my app that i am specifically having trouble with
export const fetchData = url => {
console.log("start Fetching");
return async dispatch => { // this is where the problem is
dispatch(fetchingRequest());
try {
const response = await fetch("https://randomuser.me/api/?results=10");
const json = await response.text();
if (response.ok) {
dispatch(fetchingSuccess(json));
console.log("JSON", json);
} else {
console.log("fetch did not resolve");
}
} catch (error) {
dispatch(fetchingFailure(error));
}
};
console.log("Fetched data");
};
Upon debugging the function, I have ended with finding that when the fetchData function is called the function will execute but the async dispatch that is being returned has undefined behavior.
The output in the debugger when the function is called should be
start Fetching
JSON file information/Error
but the output in the debugger is actually
start Fetching
This is the function in which fetchData is called in
_onPress = () => {
let url = "https://randomuser.me/api/?results=10";
fetchData(url);
console.log("should have fetched");
};
this is the mapDispatchToProps function that I have added. The problem is i do not know what to add inside the function.
const mapStatetoDispatch = (url, dispatch) => {
return {dispatch(fetchData(url))}; // do not know what to place in body of function
};
i have connected it in the component with
export default connect(
mapStateToProps,
mapDispatchToProps
)(App);
these are the action creators that I import, if needed
import {
fetchingSuccess,
fetchingRequest,
fetchingFailure,
fetchData
} from "../data/redux/actions/appActions.js";
Assuming you have added redux-thunk as a middleware, it looks like the errors are here:
_onPress = () => {
const { fetchData } = this.props;
let url = "https://randomuser.me/api/?results=10";
fetchData(url);
console.log("should have fetched");
};
and
const mapStatetoDispatch = dispatch => ({
fetchData: url => dispatch(fetchData(url)),
}};
I have a list of companies in React Native.
When I click on one of those companies I get the url of the API that is used for selected company. Then I store it to AsyncStorage and then I show the login screen. The function is as follows:
selectCompany(data_url, e) {
AsyncStorage.setItem("data_url", JSON.stringify(data_url), () => this.props.login());
}
Then on login page if I click on sign in button I go to the onLogin function, the function is as follows:
onLogin: function() {
fetch(data.url + '/manager/api/v1/obtain-auth-token/', })
.then(function(body) {
return body.json();
}).then(function(json) {
.....
}).catch(function() {
....
});
},
And data.url comes from data.js file, and I try to get url from the data.js file as follows:
let data_url = AsyncStorage.getItem("data_url").then(json => JSON.parse(json));
module.exports = {
url: data_url,
.....
}
But it doesn't work. Any advice?
AsyncStorage is async, therefore data_url will not be defined until it's retrieved what its looking for, you would need to move the fetch into the promise thats returned from the get so it will run it once it's done getting the data. This might be one way you tackle it:
const data_url = () => AsyncStorage.getItem("data_url"); //change this into a function
module.exports = {
url: data_url,
.....
}
now inside your component...
onLogin: function() {
data.url().then((url) => {
fetch(JSON.parse(url) + '/manager/api/v1/obtain-auth-token/', })
.then(function(body) {
return body.json();
}).then(function(json) {
.....
}).catch(function() {
....
});
});
},
AsyncStorage.getItem is a promise and needs to await for response rather than accessing direct and the function calling it should be defined as async. Here is an example to retrieve from AsyncStorage..
export async function getAccessKey(){
let accessToken = await AsyncStorage.getItem(ACCESS_TOKEN);
return accessToken;
}