React State 不会在第一次点击时更新

Question

I was trying to build a simple data displaying system with two sorting buttons (ascending & descending).

The way I did it was fetch & display data from array using map method. Then in another component file I use useEffect to trigger the sorting.

The problem is the system doesn't rerenders instantly when I first click the button. The system will only rerenders on the second time I click the button (and showing result of first click).

Fetch data:

useEffect(() => {
 fetchData();
},[])

const fetchData = () => {
 SetItems(data.items)
}

Iterate data

<div>
    {items.map((item)=>
   <Details key={item.slug} item={item} />)}
</div>

Inside the Details component,

useEffect(() => {
 if(category==='ascending'){
 const sorted = items.sort((a,b) => a.time > b.time ? 1 : -1);
 setItems(sorted);}

 if(category==='descending'){
 const sorted = items.sort((a,b) => a.time < b.time ? 1 : -1);
 setItems(sorted);}

},[category])

assign sorted data to items, useEffect should re-renders every time the category is changed.

<button onClick={()=>setCategory('ascending') />
<button onClick={()=>setCategory('descending') />

When I click on a button, the system will not rerenders, the state will only renders after I click on the second button. For example:

1. Click 'Ascending Button' -> Nothing changes.
2. Click 'Descending Button' -> Data sorted by Ascending Order.
3. Click 'Ascending Button' -> Data sorted by Descending Order.

*But the data shows correctly using console.log

Answer 1

sort() 'returns the reference to the same array', meaning when after sorting and updating your state, it checks and see's its still referencing the same array, and will not rerender. You need to copy the array when setting its state

useEffect(() => {
 if(category==='ascending'){
 const sorted = items.sort((a,b) => a.time > b.time ? 1 : -1);
 setItems([...sorted]);}

 if(category==='descending'){
 const sorted = items.sort((a,b) => a.time < b.time ? 1 : -1);
 setItems([...sorted]);}

},[category])