const ParentComponent = () => {
const [cache,setCache] = useState({});
const data = [{url:"http://.."} , {url:"http://.."} , {url:"http://.."}];
return (
data.map( item,ind => (<ChildComponent item={item} setCache={setCache} cache={cache} /> ) )
)
}
const ChildComponent = ({item,setCache,cache}) => {
const [img,setImg] = useState(null);
useEffect(() => {
const setVal = async () => {
const val = await getProfilePic(item.url); //api
setCache({...cache ,[item.url]:val})
setImg(val);
};
if(cache[item.url])
{ return setImg(cache[item.url]) }
else { setVal(); }
} ,[])
return (
<div> <img src={img} /> </div>
)
}
here the url in the array variable data can be the same. In that case, it should not call the API again but should take from the variable cache.
The problem in the above case is when the second item in the array is used for rendering child component, it's not getting the value which we set using the in the first render(using the first item in the array). How can I achieve this ?
Related
I am trying to render a dynamic list but inside the jsx rendered, I can't display any item this is my code, I've also tried with useState const [orderList, setOrderList] = useState([]) and setOrderList(prev => [...prev, childData]) but it returns me an empty array so I've opted for the classic javascript way but it won't work, it also won't console log the data inside the render
const OrdiniModuloVideoAds = () => {
let orderList = [];
const ordiniRef = ref(realtimeDatabase, "ordinazioneVideoAds/modulo/ordini");
useEffect(() => {
onValue(ordiniRef, (snapshot) => {
snapshot.forEach((childSnapshot) => {
const childData = childSnapshot.val();
orderList.push(childData);
});
console.log(orderList);
});
}, []);
return (
<StyledOrdiniModuloVideoAds>
<div className='ordiniWrapper'>
{orderList.map((i) => {
return (
<span>{i.mail}</span>
);
})}
</div>
</StyledOrdiniModuloVideoAds>
);
};
EDIT
This is the snippet with the useState:
const OrdiniModuloVideoAds = () => {
const [orderList, setOrderList] = useState([])
const ordiniRef = ref(realtimeDatabase, "ordinazioneVideoAds/modulo/ordini");
useEffect(() => {
onValue(ordiniRef, (snapshot) => {
snapshot.forEach((childSnapshot) => {
const childData = childSnapshot.val();
setOrderList((prev) => [...prev, childData])
});
console.log(orderList);
});
}, []);
return (
<StyledOrdiniModuloVideoAds>
<div className='ordiniWrapper'>
{orderList.map((i) => {
return (
<span>{i.mail}</span>
);
})}
</div>
</StyledOrdiniModuloVideoAds>
);
};
The data is actually added because it logs to me the array on the useEffect Any suggestion?
Try this solution hopefully it will fix your issue.
const OrdiniModuloVideoAds = () => {
const [orderList, setOrderList] = React.useState([]);
const ordiniRef = ref(realtimeDatabase, "ordinazioneVideoAds/modulo/ordini");
useEffect(() => {
onValue(ordiniRef, (snapshot) => {
snapshot.forEach((childSnapshot) => {
const childData = childSnapshot.val();
setOrderList(prev => ([...prev, childData])); /// Order list array is empty because you're not returning the data properly that's why it just gives you the default empty array in the console.
});
});
}, []);
return (
<StyledOrdiniModuloVideoAds>
<div className='ordiniWrapper'>
{orderList.map((i) => <span key={i.mail}>{i.mail}</span>)}
</div>
</StyledOrdiniModuloVideoAds>
);
};
This is because your map callback does not return anything:
<div className='ordiniWrapper'>
{array.map((i) => {
return (
<span>{i.mail}</span>
);
})}
</div>
Or the short version:
<div className='ordiniWrapper'>
{array.map((i) => (
<span>{i.mail}</span>
))}
</div>
I'm trying to make react not load until after an axios get requests finishes. I'm pretty rough on react all around, so sorry in advance.
I'm getting an array of objects
const { dogBreedsTest } = useApplicationData()
And I need it to be the default value of one of my states
const [dogBreeds, updateDogBreeds] = useState(dogBreedsTest);
However, I'm getting an error that my value is coming up as null on the first iteration of my app starting. How can I ensure that my value has completed my request before my app tries to use it?
Here is how I am getting the data for useApplicationData()
const [dogBreedsTest, setDogBreeds] = useState(null);
const getDogBreeds = async () => {
try{
const { data } = await axios.get('https://dog.ceo/api/breeds/list/all')
if(data) {
const newDogList = generateDogsArray(data['message'])
const generatedDogs = selectedDogs(newDogList)
setDogBreeds(generatedDogs)
}
} catch(err) {
console.log(err);
}
}
useEffect(() => {
getDogBreeds()
}, []);
return {
dogBreedsTest,
setDogBreeds
}
And I am importing into my app and using:
import useApplicationData from "./hooks/useApplicationData";
const { dogBreedsTest } = useApplicationData()
const [dogBreeds, updateDogBreeds] = useState(dogBreedsTest[0]);
const [breedList1, updateBreedList1] = useState(dogBreedsTest[0])
function handleOnDragEnd(result) {
if (!result.destination) return;
const items = Array.from(dogBreeds);
const [reorderedItem] = items.splice(result.source.index, 1);
items.splice(result.destination.index, 0, reorderedItem);
for (const [index, item] of items.entries()) {
item['rank'] = index + 1
}
updateDogBreeds(dogBreedsTest[0]);
updateBreedList1(dogBreedsTest[0])
}
return (
<div className="flex-container">
<div className="App-header">
<h1>Dog Breeds 1</h1>
<DragDropContext onDragEnd={handleOnDragEnd}>
<Droppable droppableId="characters">
{(provided) => (
<ul className="dogBreeds" {...provided.droppableProps} ref={provided.innerRef}>
{breedList1?.map(({id, name, rank}, index) => {
return (
<Draggable key={id} draggableId={id} index={index}>
{(provided) => (
<li ref={provided.innerRef} {...provided.draggableProps} {...provided.dragHandleProps}>
<p>
#{rank}: { name }
</p>
</li>
)}
</Draggable>
);
})}
{provided.placeholder}
</ul>
)}
</Droppable>
</DragDropContext>
</div>
)
error: TypeError: Cannot read property 'map' of null
(I am mapping the data later in the program)
const getDogBreeds = async () => {
try {
const { data } = await axios.get('https://dog.ceo/api/breeds/list/all')
if(data) {
const newDogList = generateDogsArray(data['message'])
const generatedDogs = selectedDogs(newDogList)
setDogBreeds(generatedDogs)
}
} catch(err) {
console.log(err);
}
}
useEffect(() => {
getDogBreeds() // -> you are not awaiting this
}, []);
Do this instead
useEffect(() => {
axios.get('https://dog.ceo/api/breeds/list/all')
.then(res => {
const newDogList = generateDogsArray(res.data['message']);
const generatedDogs = selectedDogs(newDogList);
setDogBreeds(generatedDogs);
})
.catch(err => console.log(err));
}, []);
I know this looks awful, but I don't think you should use async/await inside useEffect
Use this in your application
useEffect will update whenever dogBreedsTest is changed. In order to make it work, start with null values and update them to the correct initial values once your async operation is finished.
const { dogBreedsTest } = useApplicationData();
const [dogBreeds, updateDogBreeds] = useState(null);
const [breedList1, updateBreedList1] = useState(null);
useEffect(() => {
updateDogBreeds(dogBreedsTest[0]);
updateBreedList1(dogBreedsTest[0]);
}, [dogBreedsTest]);
The problem is, that react first render and then run useEffect(), so if you don't want to render nothing before the axios, you need to tell to react, that the first render is null.
Where is your map function, to see the code? to show you it?.
I suppose that your data first is null. So you can use something like.
if(!data) return null
2nd Option:
In your map try this:
{breedList1 === null
? null
: breedList1.map(({id, name, rank}, index) => (
<Draggable
key={id} draggableId={id} index={index}>
{(provided) => (
<li ref={provided.innerRef} {...provided.draggableProps} {...provided.dragHandleProps}>
<p>
#{rank}: { name }
</p>
</li>
)}
</Draggable> ))}
You have null, because your axios is async and react try to render before any effect. So if you say to react that the list is null, react will render and load the data from the api in the second time.
Option 1 use the optional chaining operator
dogBreedsTest?.map()
Option 2 check in the return if dogBreedsTest is an array
retrun (<>
{Array.isArray(dogBreedsTest) && dogBreedsTest.map()}
</>)
Option 3 return early
if (!Array.isArray(dogBreedsTest)) return null
retrun (<>
{dogBreedsTest.map()}
</>)
Option 4 set initial state
const [dogBreedsTest, setDogBreeds] = useState([]);
You could also add a loading state and add a loading spinner or something like that:
const [dogBreedsTest, setDogBreeds] = useState(null);
const [loading, setLoading] = useState(true)
const getDogBreeds = async () => {
setLoading(true)
try{
const { data } = await axios.get('https://dog.ceo/api/breeds/list/all')
if(data) {
const newDogList = generateDogsArray(data['message'])
const generatedDogs = selectedDogs(newDogList)
setDogBreeds(generatedDogs)
}
} catch(err) {
console.log(err);
}
setLoading(false)
}
useEffect(() => {
getDogBreeds()
}, []);
return {
dogBreedsTest,
loading,
setDogBreeds
}
Edit
Try to use a useEffect hook to update the states when dogBreedsTest got set.
const { dogBreedsTest } = useApplicationData()
const [dogBreeds, updateDogBreeds] = useState(dogBreedsTest?.[0] ?? []);
const [breedList1, updateBreedList1] = useState(dogBreedsTest?.[0] ?? [])
useEffect(() => {
updateDogBreeds(dogBreedsTest?.[0] ?? [])
updateBreedList1(dogBreedsTest?.[0] ?? [])
}, [dogBreedsTest])
I am new to React (and still new to JS too), and i am trying to build my first React project. I am fetching an API , rendering some items, and building a Search Bar that filters out the items rendered.
My filtering function is more or less working, and inside of it, i store the filtered results in let result , but How i should access those results from the return part (JSX area, i think) to loop over them?
This is my code :
import React, { useState, useEffect } from "react";
import ListItem from "./ListItem";
const List = () => {
const [data, setData] = useState();
const [input, setInput] = useState("");
const onInputChange = (event) => {
setInput(event.target.value);
const value = event.target.value.toLowerCase();
let result = [];
result = data.filter((item) =>
item.name.toLowerCase().includes(value.toLowerCase())
);
setInput(result);
};
useEffect(() => {
const getData = async () => {
const response = await fetch(
"https://rickandmortyapi.com/api/character/"
);
const obj = await response.json();
setData(obj.results);
};
getData();
}, []);
return (
<div>
<input type="text" name={input} onChange={onInputChange}></input>
{data &&
data.map((item) => {
return <ListItem key={item.id} character={item} />;
})}
</div>
);
};
export default List;
So far, I can only loop over input which contains the results, like this input && input.map((item) , but that gives me an empty array when the page is loaded , until i make a search.
You just initialise input as a string so just keep input for keeping input value not result data. You can create another state for keeping result OR put result data back on Data variable.
Here I am showing you to keep result data separate.
import React, { useState, useEffect } from "react";
import ListItem from "./ListItem";
const List = () => {
const [data, setData] = useState();
const [searchResult, setSearchResult] = useState();
const [input, setInput] = useState("");
const onInputChange = (event) => {
setInput(event.target.value);
const value = event.target.value.toLowerCase();
let result = [];
result = data.filter((item) =>
item.name.toLowerCase().includes(value.toLowerCase())
);
setSearchResult(result);
};
useEffect(() => {
const getData = async () => {
const response = await fetch(
"https://rickandmortyapi.com/api/character/"
);
const obj = await response.json();
setData(obj.results);
};
getData();
}, []);
return (
<div>
<input type="text" name={input} onChange={onInputChange}></input>
{input===""? data &&
data.map((item) => {
return <ListItem key={item.id} character={item} />;
}):
searchResult &&
searchResult.map((item) => {
return <ListItem key={item.id} character={item} />;
})
}
</div>
);
};
export default List;
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.6.3/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.6.3/umd/react-dom.production.min.js"></script>
This is separating your original data and search result different.
You need to use a variable to store data after filter:
const [data, setData] = useState([]);
const onInputChange = (event) => {
setInput(event.target.value);
};
const result = data.filter((item) =>
item.name.toLowerCase().includes(input.toLowerCase())
);
return (
...
{result?.map((item) => {
<ListItem key={item.id} character={item} />;
})}
...
)
One possible solution would be to filter while rendering,
In this scenario you would only need to save the the input value (onInputChange):
const onInputChange = (event) => {
setInput(event.target.value);
};
Then while rendering you would need to add the filtering logic:
{ // if input is not empty
data
.filter(item => item.name.includes(input.toLowerCase()))
.map((item) => {
return <ListItem key={item.id} character={item} />;
})
I'm getting data from Django Rest API and React for Frontend, and I need to create the pagination with posts. I did it all in pagination component. I created the state with current page and I'm changing it by clicking on the page button in component like this:
const Paginator = () => {
const [count, setCount] = useState(null);
const [currentPage, setCurrentPage] = useState(1);
const [totalPages, setTotalPages] = useState(null);
const [nextPage, setNextPage] = useState(null);
const [previousPage, setPreviousPage] = useState(null);
const [valid, setValid] = useState(false);
useEffect(() => {
fetch(`http://127.0.0.1:8000/api/software/?p=${currentPage}`)
.then(response => response.json())
.then(data => {
setCount(data.count);
setTotalPages(data.total_pages)
setNextPage(data.links.next);
setPreviousPage(data.links.previous);
setValid(true);
})
}, [currentPage]);
...
return (
<>
{
...
<PbStart style={style} totalPages={range(1, totalPages+1)} setCurrentPage={setCurrentPage} />
...
}
</>
);
};
const PagItem = ({key, handleClick, className, title, name }) => {
return (
<li key={key} onClick={handleClick}>
<Link to='/' className={className} title={`Go to page ${title}`}>
{name}
</Link>
</li>
);
};
const PbStart = ({ style, totalPages, setCurrentPage }) => {
return (
...
{totalPages.map(p => (
<PagItem key={p} handleClick={() => setCurrentPage(p)} title={p} name={p} />
))}
...
);
};
And in posts component I don't know how to change current page, or getting it from the paginaton component. I've written that like this:
const Softwares = () => {
const [softwares, setSoftwares] = useState([]);
const [currentPage, setCurrentPage] = useState(1);
const [valid, setValid] = useState(false);
useEffect(() => {
fetch(`http://127.0.0.1:8000/api/software/?p=${currentPage}`)
.then(response => response.json())
.then(data => {
setSoftwares(data.results);
setValid(true);
})
}, [currentPage]);
return (
<>
{
...
{softwares.map(s => (
<Article key={s.id} pathname={s.id} title={s.title} image={s.image} pubdate={s.pub_date} icon={s.category.parent.img} categoryID={s.category.id} categoryName={s.category.name} dCount={s.counter} content={s.content} />
))}
...
}
</>
);
};
So, how to do that(get the current page from pagination component or another way)?
I think a Paginator's job is only moving between pages and updating current page state. It should not be fetching data by itself, you can provide functionality to do extra work with props.
I haven't tested this, but this might be a good starting point.
With the example below you'll have a list of articles and then below it next and previous buttons.
In Softwares, as you can see I am passing the same function for handling next and previous pages, you can refactor it to have one function like onPageMove and call this function handleNext and handlePrev.
I added two separate functions if you have want to handle something different in either.
const Paginator = ({
total, // Required: Total records
startPage = 1, // Start from page / initialize current page to
limit = 30, // items per page
onMoveNext = null, // function to call next page,
onMovePrev = null, // function to call previous page
}) => {
const [currentPage, setCurrentPage] = useState(startPage);
const canGoNext = total >= limit;
const canGoPrev = currentPage > 1;
function handleNext(e) {
if (canGoNext) {
setCurrentPage((prevState) => prevState+1);
onMoveNext && onMoveNext({ currentPage });
}
}
function handlePrev(e) {
if (canGoPrev) {
setCurrentPage((prevState) => prevState-1);
onMovePrev && onMovePrev({ currentPage });
}
}
return (
<div>
<button onClick={handlePrev} disabled={!canGoPrev}>Prev</button>
<button onClick={handleNext} disabled={!canGoNext}>Next</button>
</div>
);
};
Here is how you can use Paginator in other components.
const PER_PAGE = 30; // get max # of records per page
const Softwares = () => {
const [softwares, setSoftwares] = useState([]);
const [valid, setValid] = useState(false);
const onFetchData = ({ currentPage }) => {
fetch(`http://127.0.0.1:8000/api/software/?p=${currentPage}&per_page=${PER_PAGE}`)
.then(response => response.json())
.then(data => {
setSoftwares(data.results);
setValid(true);
})
}
useEffect(() => {
onFetchData({ currentPage: 1 })
}, []);
return (
<>
{softwares.map(s => (
<Article key={s.id} pathname={s.id} title={s.title} image={s.image} pubdate={s.pub_date} icon={s.category.parent.img} categoryID={s.category.id} categoryName={s.category.name} dCount={s.counter} content={s.content} />
))}
<Paginator total={softwares.length} limit={PER_PAGE} onMoveNext={onFetchData} onMovePrev={onFetchData} />
</>
);
};
I'm making an effort to implement a loading using hooks on react.
I can do it using componentDidMount, but this applications uses Hoocks.
I create the state and the changestate, but i can not set and use it on my html.
Here is my code:
First of all i made a get request whit axios and async/await
const fetchContent = async content => {
const data = []
for await (const item of content) {
const info = await axios.get(
`url/id`
)
data.push({ componentDisplay: item.title });
}
return data
}
then i call it whit usseEffect
const ContentGroups = ({ content , ads}) => {
const [contentResult, setResult] = useState([])
const [contentLoading, changeCondition] = useState(true)
const change = () => {
changeCondition(false)
}
useEffect(
() => {
fetchContent(content).then(data => setResult(data)
change()
},
[content]
)
return (
<React.Fragment>
{ contentLoading ? <Loading /> : <Conteiner> } // always show me the container, although contentLoading innitial state is true..
</div>
</React.Fragment>
)
}