I got simple blog with arficles, and when user click edit button he got form filled with articles data - title, description, body and tags. I use useEffect to get data and fill form, when I got "id". If there is no "id" form should be blank. here is my useEffect:
useEffect(() => {
if (id) {
isLoading = true;
return props.onLoad(userService.articles.get(id));
}
props.onLoad(null);
}, [id]
);
but when I reload page id not changed, and func userService.articles.get(id) not run, and all datas gone. I need advice how to fix it? may be I need to use other deps for useEffect, but now I have no idea what deps i can use exept id.
upd:
thank you all for help. all i want is:
when the edit page load/reload and "id" exist -> fills form fields
when "id" not exist -> blank form fields
now when I reload edit page i got id - but all datas gone, and i got blank form :(
Here is the full code: codesandbox
p.s. i use free API - so you can create user in a sec with any imagined email, username and password. you don't need mail confirmation.
You should use this.props.match.params to access your id that comes from the url.
useEffect(() => {
if (props.match.params.id) {
setIsloading(true);
userService.articles.get(props.match.params.id)
.then((resp) => {
setIsloading(false);
props.onLoad(resp)
})
} else {
props.onLoad(null);
}
}, [props.match.params.id]);
Also you should rely on useState to manage your isLoading variable.
const [isLoading, setIsloading] = useState(false);
I did a bit more digging into the code you have provided.
The initialValues will be first empty because the data coming from the props is not there yet. And once the initialValues have been set you can't change them dynamically, you have to resort to the antd Form api.
You cannot set value for each form control via value or defaultValue
prop, you should set default value with initialValues of Form. Note that initialValues cannot be updated by setState dynamically, you
should use setFieldsValue in that situation.
The key here is to use another useEffect with dependencies to your form values comming from the props and use those to reset the form values via setFieldsValue.
try to useEffect without options and it will run just when the page loads for the first time
useEffect(() => {
if (id) {
isLoading = true;
return props.onLoad(userService.articles.get(id));
}
props.onLoad(null);
}, []
);
Based on the assumption that you want props.onLoad to run whenever there is a defined "id" or the defined "id" changes:
Returning a function from a useEffect hook (as you do with return props.onLoad(...)) is specifically for "cleaning up" things like side effects or subscriptions. A function returned inside a useEffect hook will only run when the component unmounts. See docs here. Also it doesn't seem like you are even passing a function to run on cleanup. You're passing the result of props.onLoad to run on cleanup, which based on the function name doesn't seem like it is intended to return another function.
So, if you want props.onLoad() to run if the "id" is defined, remove the return before props.onLoad. That return is telling React to hold (what it thinks is a function) for cleanup on unmount. If it's still not working, I think we'll need more information on what exactly props.onLoad is doing.
Related
I'm using Inertia.js and I've been loving it.
I'm having a problem anyway that I cant seem to figure out. I have a select input that will contain options from the database but a lot of them aprox. 30/40k so my idea is to just take the first 20 and then let the user input a search and bring the first 20 that match that result.
All my backend is working ok but the problem I'm having is displaying the updated select options after search.
The relevant code is the following: First the call to AsyncSelect Component from the react-select package. This components needs a loadOptions property that will call a function when the user start typing
<AsyncSelect
name="proveedores"
id="proveedores"
defaultOptions={proveedores}
loadOptions={handleChange}
/>
The function that gets call is this, it recieves the input value and a callback, within this callback I'm supposed to search for the new data and return it
function handleChange(inputValue,callback) {
setValues(values => ({
...values,
["search"]: inputValue
}));
callback()
}
The problem is that to load the new data on search I'm using useEffect
useEffect(() => {
if (prevValues) {
const query = pickBy(values)
Inertia.get(window.location.href, query, {
replace: true,
preserveState: true
});
}
}, [values]);
The search with useEffect works ok, if I do a console.log I will see the list of proveedores updated but the problem is how do I tell the callback from handleChange function that it should listen for useEffect and on finish use the new value of proveedores
If anyone had to do something like this (React Select with search data from database) using Inertia + React, i would really appreciate some feedback on how to achieve it.
Thanks!!
According to the documentation of SWR: React Hooks for Data Fetching, there is an options object which can be passed in for more control of the hook.
The documentation mentions a compare option:
compare(a, b): comparison function used to detect when returned data
has changed, to avoid spurious rerenders. By default, dequal is used.
Is it something like this?
export function useUser(shouldAPIBeCalled = false) {
const { data: user, error, mutate } = useSWR(() => shouldAPIBeCalled ? '/api/user' : null, fetcher, {
compare: (_old, _new) => {
return dequal(_old, _new);
}
})
Essentially I don't want the fetcher to be called if we haven't changed the original object in my case:
If the user is still...
user: null // don't make that call again
Don't make another call because it hasn't changed!
What’s happening to me is the hook keeps firing.
I only have the hook in a Layout component to show hide navigation elements if we have a user or not,
In the submit function of the login to get the mutate function to update the user,
And in the Auth component (which wraps certain pages) to check if a user is authorized.
Thanks in advance!
I am using react native navigation and have two tabs. One of them has a list of entites, the other has a form to submit entities. When ever a new entity is submitted, I'd like to refresh the first tab to be sure, the newest data gets loaded.
I navigate to the first tab like this:
navigation?.navigate('Main', {refresh: true});
This props gets saved as follows:
let {refresh} = route.params;
To check, if the screen needs to refresh, I added a listener in useEffect() like this:
useEffect(() => {
const unsubscribe = navigation.addListener('focus', () =>{
if(refresh){
doRefresh()
}
})
}, [])
Unfortunately, neither "refresh" nor "route.params" directly is ever true inside the listener. Passing the param works, because I took a closer look at the var and it gets true, whenever I submit.
Do I need to access the route.params inside a navigation listener in another way?
Thanks and hit me up, if you need more information on this
The issue is that your useEffect only runs once as your dependencies array [] is empty, and therefore your listener only receives the initial value of refresh.
You need to pass refresh as a dependency to useEffect, and I don't think you even need the focus listener in your case so you would end up with this:
useEffect(() => {
if (refresh) {
doRefresh()
}
}, [refresh])
const onPressCountry = (item,index) => {
navigation.push('SignUp2', {selectedCountryId:item?.countryID, selectedCountryName: item?.name} )
}
use navigation.push instead of navigation.navigate
Edit: SOLVED! Please see below.
I want my Blog component to fire the fetchBlog action creator every time the browser requests its URL, be it via a link or a refresh. I'd like to do it with the React useEffect Hook and with the React-Redux useDispatch and useSelector Hooks. However, my action only fires when following the link to the page; I do not understand why, even after reading several explanations (like the official docs).
Here is the code:
// Everything duly imported, or else VSC would yell at me
export default function Blog() {
const dispatch = useDispatch();
// slug is set here with useSelector, this always works
useEffect(() => {
dispatch(fetchBlog(slug))
}, [slug, dispatch]);
const blog = useSelector((state) => state.blogs[0]);
// return renders the blog information from the blog constant
// since the action does not fire, blog is undefined because state.blogs is an empty array
}
I know that, on refresh, fetchBlog does not fire because of Redux DevTools and also because I put a debugger there. (And the back-end logs don't show the request coming in.) The action creator itself and the reducer must be working; if they weren't, the page would not load correctly when visited through a link.
Edit: I have determined useSelector and useDispatch are not the root cause of the problem, as changing the code to use connect with mapStateToProps and mapDispatchToProps gives the same result. The issue seems to be with useEffect.
I think the problem is you are returning the call to dispatch. Functions returned from useEffect are clean up functions, so I don't think this would run on mount, or update - only before unmount. Try this:
export default function Blog() {
// ...
// Don't return from useEffect. Just call dispatch within the body.
useEffect(() => {
dispatch(fetchBlog(slug);
}, [slug, dispatch]);
// ...
}
https://reactjs.org/docs/hooks-reference.html#cleaning-up-an-effect
I'd like to clarify what the issue was, which #Trace guided me to finding.
useEffect wasn't being called on refresh because it gets called after the component renders/returns. When refreshing, the state - including the blog data - is lost; instead of returning, a TypeError is thrown because data.title doesn't exist. So useEffect never gets the chance of being called and fetch the blog's content.
The solution to that goes like this:
export default function Blog() {
// ...
useEffect(/* ... */)
const blog = useSelector((state) => state.blogs[0]);
if (!blog) {
return <p>Loading...</p>
}
// return actual blog contents here
}
So now fetchBlog does get called, updating blog and rendering the content.
It isn't clear to me where the slug comes from.
In theory useEffect runs after every render. In case of multiple parameters it will run the callback when one of the array parameters passed in the second argument changes.
Either create a useEffect with empty array as second argument to run it 'once' (e.g. when you refresh) or check the slug value.
Edits after checking the repo:
It's not going to work because useEffect is run AFTER the render (which was included in my answer although someone downvoted it). Dispatching the call will only happen after, or not at all if the exception was thrown before (in this case a nullpointer).
You can get the slug from react-router with match, may be handy for you to know.
export default function Blog({ match }) {
const slug = match.params.slug;
etc
The git repo shows how dispatch as is added as array parameter to useEffect, which is not necessary.
I am trying to use react hooks to make a Table component that displays rows of data from an API based on a set of filters that the user can choose. I want to make a new call to fetch data whenever the user clicks an 'Apply Filters' button, not when the user makes changes to the filters.
I am using context to manage the 'filters' state and a 'lastFetched' state which tracks when the user last clicked the 'Apply Filters' button (as well as other states on the page). Updates to the context are made via the useReducer hook and its dispatch method (see here).
The data fetching occurs in a useEffect hook that reruns whenever the 'lastFetched' state changes. This appears to be working correctly; however, the effect references other values from the context (i.e. the filters) that are not included in the dependencies. I am aware of the exhaustive-deps eslint rule, and I am concerned that I am not handling the hook's dependencies correctly.
const Table = () => {
const [context, dispatch] = useTableContext(); // implemented with createContext and useReducer
const { filters, lastFetched } = context;
useEffect(() => {
if (!filters.run) {
return;
}
dispatch({ type: 'FETCH_DATA_BEGIN' });
const params = convertContextToParams(context); // this is lazy, but essentially just uses the the filters and some other state from the context
API.fetchData(params)
.then((data) => {
dispatch({ type: 'FETCH_DATA_SUCCESS', payload: data.results });
})
.catch((e) => {
dispatch({ type: 'FETCH_DATA_FAILURE', payload: e.response.data.message });
});
return () => { ... some cleanup... };
}, [lastFetched]); // <== This is the part in question
return <...some jsx.../>
};
Again, this appears to be working, but according to the react docs, it seems I should be including all the values from the context used in the hook in the hook's dependencies in order to prevent stale references. This would cause the logic to break, since I don't want to fetch data whenever the filters change.
My question is: when the user clicks 'Apply Filters', updates context.lastFetched, and triggers the useEffect hook, will the hook be referencing stale filter state from the context? If so, why? Since the effect is rerun whenever the button is clicked, and all the state updates are done via a reducer, does the usual danger of referencing stale variables in a closure still apply?
Any guidance appreciated!
Note: I have thought about using useRef to prevent this issue, or perhaps devising some custom async middleware to fetch data on certain dispatches, but this is the solution I currently have.
I am not an expert but I would like to provide my takes. According to my understanding of how Context works, you will not get stale filter data with the current implementation. useReducer updates the state with a new object which will trigger Table to be re-render.
Also, Table component doesn't really care about filter data unless lastFetched is changed by a click event. If lastFetched is changed, all the Consumer of TableContext will be re-render again. You should not get stale filter data either.