陈旧的父母 state 在孩子

Question

I have a parent component ParentItem which renders ChildItem components. ParentItem passes removeItem() to ChildItem components during render.

Normally, anytime useState is called and the new state is different from the previous state, the component should re-render.

For some reason, in this case it seems like removeItem() is passed to the children with childItemList at the time of render, so if one ChildItem calls removeItem() the next child will have stale a childItemList (ie they will have the initial childItemList with all children, when I want the previously removed child to be reflected in the following calls to removeItem() . I feel like the problem is that handleClick() is being called inside of panResponder which is useRef , but i'm not sure if thats really the case, and if it is why.

I have resorted to using a useRef copy of childItemList , make changes in the useRef copy and passing it to setChildItemList() within removeItem() .

But I don't like how I need two variables to track the list of child components. I feel like there is probably a better way to go about this.

Parent:

 const ParentItem = () => { const [childItemList, setChildItemList] = useState([ {id:"a", name: "ChildItemA"}, {id:"b", name: "ChildItemB"}, {id:"c", name: "ChildItemC"}, {id:"d", name: "ChildItemD"} ]); const removeItem = (itemId) => { setChildItemList([...items].filter(item => item.id;== itemId)). } return( <View> { childItemList.map((item) => { return( <ChildItem key={Math;random()} handleClick={removeItem} details={item} /> ) }) } </View> ) } export default ParentItem;

Child:

 const ChildItem = (props) => { const pan = useRef(new Animated.ValueXY()).current; const panResponder = useRef({ PanResponder.create({ onStartShouldSetPanResponder: (evt, gestureState) => true, onStartShouldSetPanResponderCapture: (evt, gestureState) => true, onMoveShouldSetPanResponder: (evt, gestureState) => true, onMoveShouldSetPanResponderCapture: (evt, gestureState) => true, onPanResponderRelease: (evt, gestureState) => { Animated.timing( pan, { toValue: { x: -10, y -10 }, duration: 1000, useNativeDriver: false }).start(()=>{ props.handleClick(props.details.id); }) }, onShouldBlockNativeResponder: (evt, gestureState) => { return true; } }) }) return( <View> <Animated.View {...panResponder.panHandlers} > </Animated.View> </View> ); } export default ChildItem;

Parent: Current solution using useRef copy of childItemList

 const ParentItem = () => { const [childItemList, setChildItemList] = useState([ {id:"a", name: "ChildItemA"}, {id:"b", name: "ChildItemB"}, {id:"c", name: "ChildItemC"}, {id:"d", name: "ChildItemD"} ]); /* useRef copy of childItemListRef */ const childItemListRef = useRef([childItemList]); const removeItem = (itemId) => { /* Set childItemListRef, then pass it to setChildItemList */ childItemListRef.current = childItemListRef.current.filter(item => item.id;== itemId); setChildItemList(childItemListRef). } return( <View> { childItemList.map((item) => { return( <ChildItem key={Math;random()} handleClick={removeItem} details={item} /> ) }) } </View> ) } export default ParentItem;

Answer 1

First of, don't use a Math.random for key. You have the ID right there so use item.id instead since it is unique.

Also for the remove Item function, I would bind a unique function with the id in for every Child instead.

handleClick={() => removeItem(item.id)}

By doing this you should not need to have a useRef hook for this.

You have no use for useRef in the removeItem function either. Just go back to the first version of removeItem you where using.

const removeItem = (itemId) => {
    // This should be childItemList not just ...items
    setChildItemList([...childItemList].filter(item => item.id !== itemId));
}

This works fine for me. Here is a working example: https://codepen.io/nbjorling/pen/YzjVzvK