I'm passing an array of objects to a child as props, and I wanted the child component to re-render when the aray changes, but it doesn't:
parent:
export default function App() {
const [items, setItems] = useState([]);
const buttonCallback = () => {
setItems([...items, { text: "new item" }]);
};
return (
<div className="App">
<h1>Items list should update when I add item</h1>
<button onClick={buttonCallback}>Add Item</button>
<Items />
</div>
);
}
child:
const Items = ({ itemlist = [] }) => {
useEffect(() => {
console.log("Items changed!"); // This gets called, so the props is changing
}, [itemlist]);
return (
<div className="items-column">
{itemlist?.length
? itemlist.map((item, i) => <Item key={i} text={item.text + i} />)
: "No items"}
<br />
{`Itemlist size: ${itemlist.length}`}
</div>
);
};
I found this question with the same issue, but it's for class components, so the solution doesn't apply to my case.
<Items propsname={data} />
const buttonCallback = () => {
setItems([...items, { text: "new item" }]);
};
but you should put it as:
const buttonCallback = () => {
setItems([...items, { text: "new item", id: Date.now() }]);
};
Because is not recommended to use index as a key for react children. Instead, you can use the actual date with that function. That is the key for React to know the children has changed.
itemlist.map((item) => <Item key={item.id} text={item.text} />)
Try below: you are adding array as a dependency, to recognise change in variable, you should do deep copy or any other thing which will tell that useEffect obj is really different. `
const Items = ({ itemlist = [] }) => {
const [someState,someState]=useState(itemlist);
useEffect(() => {
someState(itemlist)
}, [JSON.stringify(itemlist)]);
return (
<div className="items-column">
{someState?.length
? someState.map((item, i) => <Item key={i} text={item.text
+ i}
/>)
: "No items"}
<br />
{`Itemlist size: ${someState.length}`}
</div>
);
};