I am using react usestate() and I want to update device state(It is an object)
my problem is when ShowRelays component renders for the first time device is an empty object and It does not get updated during first rendering, but for the next renders everything is fine
How can I update device state for the first time rendering?
(sorry for my bad english)
.
function ShowRelays(props) {
const [device, setDevice] = useState({})
let reduxDevices = useSelector(state => state.devicesReducer.devices)
let findDevice = () => {
let myDevice = reduxDevices.find(x => x._id === props.id)
setDevice(prevState => {
return {
...prevState,
...myDevice
}
})
}
useEffect(() => {
if (props.show) {
findDevice()
}
}, [props.show])
return
(
<div>
test
</div>
)
}
myDevice object is like:
{active: true, name: "device1", id: "deviceId"}
You can pass a function to your useState-hook which will calculate your initial value for device.
see lazy init state
function ShowRelays(props) {
let reduxDevices = useSelector(state => state.devicesReducer.devices);
const [device, setDevice] = useState(() => {
return reduxDevices.find(x => x._id === props.id)
});
return <div>test</div>;
}
An other possible solution for your problem without using a separate state could be the following (directly select the right device from your selector function):
function ShowRelays(props) {
const device = useSelector(state => {
return state.devicesReducer.devices.find(x => x._id === props.id);
});
return <div>test</div>;
}
Related
On my current application, if a user tries to enter an existing name that has a different number, it will prompt the user if they want to update that entry with the new number. If yes, the entry is updated using an axios PUT request. My issue is that I can only get it to change on the front end by reloading the page (it updates successfully on db.json) instead of it updating immediately after the user confirms. On my useEffect method I tried adding [persons] as the second argument and it seemed to work, but found out that it loops the GET requests infinitely. I have a similar function for when deleting an entry so I'm sure it must be something that has to be added to setPersons
Update methods
const addEntry = (event) => {
event.preventDefault();
const newPersonEntry = {
name: newName,
number: newNumber,
}
const all_names = persons.map(person => person.name.toUpperCase())
const all_numbers = persons.map(person => person.number)
const updatedPerson = persons.find(p => p.name.toUpperCase() === newName.toUpperCase())
const newPerson = { ...updatedPerson, number: newNumber };
if (newName === '') {
alert('Name entry cannot be blank')
return
}
if (newNumber === '') {
alert('Number entry cannot be blank')
return
}
if (all_numbers.includes(newNumber)) {
alert('That number already exists')
return
}
if (newNumber.length < 14) {
alert('Enter a valid number')
return
}
if (all_names.includes(newName.toUpperCase())) {
if (window.confirm(`${newName} already exists, replace number with the new one?`)) {
console.log(`${newName}'s number updated`)
personService
.update(updatedPerson.id, newPerson)
.then(res => {
setPersons() //something here
})
return
}
return
}
personService
.create(newPersonEntry)
.then(person => {
setPersons(persons.concat(person))
setNewName('')
setNewNumber('')
})
}
//PUT exported as personService
const update = (id, newObject) => {
const request = axios.put(`${baseURL}/${id}`,newObject)
return request.then(response => response.data)
}
Other code
const App = () => {
const [persons, setPersons] = useState([])
useEffect(() => {
personService
.getAll()
.then(initialPersons => {
setPersons(initialPersons)
})
}, [])
...
//Display method
const filteredNames = persons.filter(person => person.name.toLowerCase().includes(filter.toLowerCase()))
const row_names = () => {
return (
filteredNames.map(person =>
<p key={person.id}>{person.name} {person.number} <button onClick={() => handleDelete(person)}>delete</button></p>));
}
...
//Render
return (
<div>
<h2>Phonebook</h2>
<h2>Search</h2>
<SearchFilter value={filter} onChange={handleFilterChange} />
<h2>Add Entry</h2>
<Form onSubmit={addEntry}
name={{ value: newName, onChange: handleNameChange }}
number={{ value: newNumber, onChange: handleNumberChange }}
/>
<h2>Numbers</h2>
<DisplayPersons persons={row_names()} />
</div>
)
}
The solution here is a little bit tricky but doable . You need to split your logic into two parts like this :
const [dataChanged , setDataChanged] = useState(false)
useEffect(()=>{
// Rest of your logic here
} , [dataChanged])
useEffect(()=>{
// Your logic will run only one time
// on Success we change the dataChanged state so the other useEffect will
// run basically you can run the rest of your logic in the other
// useEffect so the infinite loop won't happen
// setDataChanged( (prev) => !prev )
} , [])
Was able to use map method that worked
personService
.update(updatedPerson.id, newPerson)
.then(res => {
setPersons(persons.map(p => p.id !== updatedPerson.id ? p : res))
})
I have a set of card objects that I map over.
When I click on a card it adds the selected class which in turn gives it a border to show the user it is selected, it also adds the id of the card to the selectedCards useState array.
WHAT I WANT TO HAPPEN:
Each card object has a creditAvailable key state which is equal to a figure.
On selection (click) of the card, in addition to selecting the card I would also like to add up the creditAvailable and display it on the screen. and when I unselect the card I would like the figure to go down.
WHAT I HAVE TRIED:
I thought it would be as simple as calling the function to add up the credit inside the first function which selects the card, however when console logging inside the first function I see that the state has not yet updated. (scope).
I then tried to call the function outside of the first function but it gave me an infinite loop. Here is my code.
Any ideas? Thanks
const [cards, setCards] = useState([]);
const [selectedCards, setSelectedCards] = useState([]);
const [total, setTotal] = useState();
const handleSelectCard = (id) => {
if (selectedCards.includes(id)) {
const filteredIds = selectedCards.filter((c) => c !== id);
setSelectedCards([...filteredIds]);
} else {
setSelectedCards([...selectedCards, id]);
}
// addUpCreditAvailable(); // nothing happens
console.log(selectedCards); // []
};
console.log(selectedCards) // [1] for example. This is in the global scope
const addUpCreditAvailable = () => {
console.log("inside add up credit");
const chosenCards = selectedCards.map((id) => {
const foundCard = allCards.find((card) => {
return card.id === id;
});
return foundCard;
});
const result = chosenCards.reduce((acc, card) => {
return acc + card.creditAvailable;
}, 0);
setTotal(result);
return result;
};
return (
<div className="Container">
<UserInputForm submitData={handleSubmitData} />
<h1> Cards available to you displayed are below!</h1>
{cards.map(
({
id,
name,
number,
apr,
balanceTransfer,
purchaseDuration,
creditAvailable,
expiry,
}) => (
<CreditCard
key={id}
name={name}
number={number}
apr={apr}
balanceTransferDuration={balanceTransfer}
purchaseOfferDuration={purchaseDuration}
creditAvailable={creditAvailable}
expiry={expiry}
onClickCard={() => handleSelectCard(id)}
selected={selectedCards.includes(id)}
/>
)
)}
<span> £{total}</span>
)}
I figured it out with the help from above. As Wilms said i had to return the result of the handleSelectCard function and return the result of the addUpCredit function. Then I called the addUpCreditAvailable with the selectedCards state and stored the result in a variable which i then displayed in my render method.
const [cards, setCards] = useState([]);
const [selectedCards, setSelectedCards] = useState([]);
const handleSelectCard = (id) => {
if (selectedCards.includes(id)) {
const filteredIds = selectedCards.filter((c) => c !== id);
setSelectedCards([...filteredIds]);
} else {
setSelectedCards([...selectedCards, id]);
}
return selectedCards;
};
const addUpCreditAvailable = (selectedCards) => {
const chosenCards = selectedCards.map((id) => {
const foundCard = allCards.find((card) => {
return card.id === id;
});
return foundCard;
});
const result = chosenCards.reduce((acc, card) => {
return acc + card.creditAvailable;
}, 0);
return result;
};
const totalCredit = addUpCreditAvailable(selectedCards);
render method:
render (
[...]
{selectedCards.length && (
<div className={bem(baseClass, "total-credit")}>
Total Credit available: £{totalCredit}
</div>
)}
[...]
)
I have states :
const { id } = useParams<IRouterParams>();
const [posts, setPosts] = useState<IPost[]>([]);
const [perPage, setPerPage] = useState(5);
const [fetchError, setFetchError] = useState("");
const [lastPostDate, setLastPostDate] = useState<string | null>(null);
// is any more posts in database
const [hasMore, setHasMore] = useState(true);
and useEffect :
// getting posts from server with first render
useEffect(() => {
console.log(posts);
fetchPosts();
console.log(hasMore, lastPostDate);
return () => {
setHasMore(true);
setLastPostDate(null);
setPosts([]);
mounted = false;
return;
};
}, [id]);
When component change (by id), I would like to clean/reset all states.
My problem is that all states are still the same, this setState functions in useEffect cleaning function doesn't work.
##UPDATE
// getting posts from server
const fetchPosts = () => {
let url;
if (lastPostDate)
url = `http://localhost:5000/api/posts/getPosts/profile/${id}?limit=${perPage}&date=${lastPostDate}`;
else
url = `http://localhost:5000/api/posts/getPosts/profile/${id}?limit=${perPage}`;
api
.get(url, {
headers: authenticationHeader(),
})
.then((resp) => {
if (mounted) {
if (resp.data.length === 0) {
setFetchError("");
setHasMore(false);
setPosts(resp.data);
return;
}
setPosts((prevState) => [...prevState, ...resp.data]);
if (resp.data.length < perPage) setHasMore(false);
setLastPostDate(resp.data[resp.data.length - 1].created_at);
setFetchError("");
}
})
.catch((err) => setFetchError("Problem z pobraniem postów."));
};
if your component isnt unmounted, then the return function inside useEffect will not be called.
if only the "id" changes, then try doing this instead:
useEffect(() => {
// ... other stuff
setHasMore(true);
setLastPostDate(null);
setPosts([]);
return () => { //...code to run on unmount }
},[id]);
whenever id changes, the codes inside useEffect will run. thus clearing out your states.
OK, I fixed it, don't know if it is the best solution, but works...
useEffect(() => {
setPosts([]);
setHasMore(true);
setLastPostDate(null);
return () => {
mounted = false;
return;
};
}, [id]);
// getting posts from server with first render
useEffect(() => {
console.log(lastPostDate, hasMore);
hasMore && !lastPostDate && fetchPosts();
}, [lastPostDate, hasMore]);
I have a component like this. What I want is for the useEffect function to run anytime myBoolean changes.
I could accomplish this by setting the dependency array to [myBoolean]. But then I get a warning that I'm violating the exhaustive-deps rule, because I reference myArray inside the function. I don't want to violate that rule, so I set the dependency array to [myBoolean, myArray].
But then I get an infinite loop. What's happening is the useEffect is triggered every time myArray changes, which is every time, because it turns out myArray comes from redux and is regenerated on every re-render. And even if the elements of the array are the same as they were before, React compares the array to its previous version using ===, and it's not the same object, so it's not equal.
So what's the right way to do this? How can I run my code only when myBoolean changes, without violating the exhaustive-deps rule?
I have seen this, but I'm still not sure what the solution in this situation is.
const MyComponent = ({ myBoolean, myArray }) => {
const [myString, setMyString] = useState('');
useEffect(() => {
if(myBoolean) {
setMyString(myArray[0]);
}
}, [myBoolean, myArray]
}
Solution 1
If you always need the 1st item, extract it from the array, and use it as the dependency:
const MyComponent = ({ myBoolean, myArray }) => {
const [myString, setMyString] = useState('');
const item = myArray[0];
useEffect(() => {
if(myBoolean) {
setMyString(item);
}
}, [myBoolean, item]);
}
Solution 2
If you don't want to react to myArray changes, set it as a ref with useRef():
const MyComponent = ({ myBoolean, myArray }) => {
const [myString, setMyString] = useState('');
const arr = useRef(myArray);
useEffect(() => { arr.current = myArray; }, [myArray]);
useEffect(() => {
if(myBoolean) {
setMyString(arr.current);
}
}, [myBoolean]);
}
Note: redux shouldn't generate a new array, every time the state is updated, unless the array or it's items actually change. If a selector generates the array, read about memoized selectors (reselect is a good library for that).
I have an idea about to save previous props. And then we will implement function compare previous props later. Compared value will be used to decide to handle function change in useEffect with no dependency.
It will take up more computation and memory. Just an idea.
Here is my example:
function usePrevious(value) {
const ref = useRef();
useEffect(() => {
ref.current = value;
});
return ref.current;
}
function arrayEquals(a, b) {
return Array.isArray(a) &&
Array.isArray(b) &&
a.length === b.length &&
a.every((val, index) => val === b[index]);
}
const MyComponent = ({ myBoolean, myArray }) => {
const [myString, setMyString] = useState('');
const previousArray = usePrevious(myArray);
const previousBoolean = usePrevious(myBoolean);
const handleEffect = () => {
console.log('child-useEffect-call-with custom compare');
if(myBoolean) {
setMyString(myArray[0]);
}
};
//handle effect in custom solve
useEffect(() => {
//check change here
const isEqual = arrayEquals(myArray, previousArray) && previousBoolean === myBoolean;
if (!isEqual)
handleEffect();
});
useEffect(() => {
console.log('child-useEffect-call with sallow compare');
if(myBoolean) {
setMyString(myArray[0]);
}
}, [myBoolean, myArray]);
return myString;
}
const Any = () => {
const [array, setArray] = useState(['1','2','3']);
console.log('parent-render');
//array is always changed
// useEffect(() => {
// setInterval(() => {
// setArray(['1','2', Math.random()]);
// }, 2000);
// }, []);
//be fine. ref is not changed.
// useEffect(() => {
// setInterval(() => {
// setArray(array);
// }, 2000);
// }, []);
//changed ref but value in array are not changed -> handle this case
useEffect(() => {
setInterval(() => {
setArray(['1','2', '3']);
}, 2000);
}, []);
return <div> <MyComponent myBoolean={true} myArray={array}/> </div>;
}
I have to get a users from backend and push the result array into a property of third-party component. I can't push the result into the component's state, like setUsersList, because it leads to infinity render-loop. So I decided to use a function which will put the data from backend into a variable and return variable's value.
<InputAutocomplete
...
value={selectedUserName}
onChange={(value: string) => setSelectedUserName(value)}
options={getFilteredUsers(selectedUserName)}
/>
My function is:
const getFilteredUsers = (typedValue: any): any[] => {
console.log('***getting into getFilteredUsers method')
if (!typedValue) {
return []
}
let usersList: any[]
repository.GetUsers(typedValue).then((response) => {
if (response.StatusCode !== null) {
response.Message.then((errorText) => showNotificationPopup(errorText, consts.ERROR_OCCURED, 'error'))
return
}
response.Data.then((users) => {
console.log('filling usersList')
usersList = (users.map((u) => {
return {key: u.Id, value: `${u.Name} - ${u.Position} - ${u.DopOfficeName}` }
})
)
})
})
console.log('leaving function')
return usersList
}
It works unacceptable for me (although it works as expected):
***getting into getFilteredUsers method
leaving function (with empty array)
filling usersList (too late)
The property "options" of third's party component doesn't accept Promise<any[]>, it can only accept any[], thus I can't mark my function as async and await the result from repository before to leave the function.
How to prevent leaving function before I'll get the result?
Maybe I've made a wrong decision at all. If I'm wrong I need a help, how to implement server-side refilling of autocomplete input component.
I can't push the result into the component's state, like setUsersList, because it leads to infinity render-loop
This should not be the case.
const SomeComponent = () => {
const [options, setOptions] = React.useState([]);
const [username, setUsername] = React.useState([]);
React.useEffect(() => {
if (!typedValue) return [];
repository.GetUsers(typedValue).then((response) => {
if (response.StatusCode !== null) {
response.Message.then((errorText) => showNotificationPopup(errorText, consts.ERROR_OCCURED, 'error'));
return;
}
response.Data.then((users) => {
console.log('filling usersList');
const usersList = users.map(u => {
return { key: u.Id, value: `${u.Name} - ${u.Position} - ${u.DopOfficeName}`};
});
setOptions(usersList);
})
})
console.log('leaving function')
}, [username]);
return (
<InputAutocomplete
value={username}
onChange={(value) => setUsername(value)}
options={options}
/>
);
};
Above code should not go in infinite loop.