I have a page wherein there are Listings. A user can check items from this list.
Whenever the user checks something it gets added to a globally declared Set(each item's unique ID is added into this set). The ID's in this set need to be accessed by a seperate Component(lets call it PROCESS_COMPONENT
) which processes the particular Listings whose ID's are present in the set.
My Listings code roughly looks like:
import React from "react";
import { CheckBox, PROCESS_COMPONENT } from "./Process.jsx";
const ListItem = ({lItem}) => {
return (
<>
//name,image,info,etc.
<CheckBox lId={lItem.id}/>
</>
)
};
function Listings() {
// some declarations blah blah..
return (
<>
<PROCESS_COMPONENT /> // Its a sticky window that shows up on top of the Listings.
//..some divs and headings
dataArray.map(item => { return <ListItem lItem={item} /> }) // Generates the list also containing the checkboxes
</>
)
}
And the Checkbox
and the PROCESS_COMPONENT
functionality is present in a seperate file(Process.jsx
).
It looks roughly like:
import React, { useEffect, useState } from "react";
let ProcessSet = new Set(); // The globally declared set.
const CheckBox = ({lID}) => {
const [isTicked, setTicked] = useState(false);
const onTick = () => setTicked(!isTicked);
useEffect( () => {
if(isTicked) {
ProcessSet.add(lID);
}
else {
ProcessSet.delete(lID);
}
console.log(ProcessSet); // Checking for changes in set.
}, [isTicked]);
return (
<div onClick={onTick}>
//some content
</div>
)
}
const PROCESS_COMPONENT = () => {
const [len, setLen] = useState(ProcessSet.size);
useEffect( () => {
setLen(ProcessSet.size);
}, [ProcessSet]); // This change is never being picked up.
return (
<div>
<h6> {len} items checked </h6>
</div>
)
}
export { CheckBox, PROCESS_COMPONENT };
The Set itself does get the correct ID values from the Checkbox
. But the PROCESS_COMPONENT
does not seem to be picking up the changes in the Set and len
shows 0(initial size of the set).
I am pretty new to react. However any help is appreciated.
Edit:
Based on @jdkramhoft
's answer I made the set into a state variable in Listings
function.
const ListItem = ({lItem,set,setPSet}) => {
//...
<CheckBox lID={lItem.id} pset={set} setPSet={setPSet} />
)
}
function Listings() {
const [processSet, setPSet] = useState(new Set());
//....
<PROCESS_COMPONENT set={processSet} />
dataArray.map(item => {
return <ListItem lItem={item} set={processSet} setPSet={setPSet} />
})
}
And corresponding changes in Process.jsx
const CheckBox = ({lID,pset,setPSet}) => {
//...
if (isTicked) {
setPSet(pset.add(lID));
}
else {
setPSet(pset.delete(lID));
}
//...
}
const PROCESS_COMPONENT = ({set}) => {
//...
setLen(set.size);
//...
}
Now whenever I click the check box I get an error:
TypeError: pset.add is not a function. (In 'pset.add(lID)', 'pset.add' is undefined)
Similar error occurs for the delete function as well.
CodePudding user response:
First of all, the set should be a react state const [mySet, setMySet] = useState(new Set());
if you want react to properly re-render with detected changes. If you need the set to be available to multiple components you can pass it to them with props or use a context.
Secondly, React checks if dependencies like [ProcessSet]
has been changed with something like ===
. Even though the items in the set are different, no change is detected because the object is the same and there is no re-render.
Update:
The setState
portion of [state, setState] = useState([]);
is not intended to mutate the previous state - only to provide the next state. So to update your set you would do something like:
const [set, setSet] = useState(new Set())
const itemToAdd = ' ', itemToRemove = ' ';
setSet(prev => new Set([...prev, itemToAdd]));
setSet(prev => new Set([...prev].filter(item => item !== itemToRemove)));
As you might notice, this makes adding and removing from a set as slow as a list. So unless you need to make a lot of checks with set.has()
I'd recommend using a list:
const [items, setItems] = useState([])
const itemToAdd = ' ', itemToRemove = ' ';
setItems(prev => [...prev, itemToAdd]);
setItems(prev => prev.filter(item => item !== itemToRemove));