Endless loop in React Native with an array of objects using the useEffect hook

For the current project I am working on, I am facing the challenge of retrieving selected items from a Flatlist and passing them to the parent component.

To tackle this issue, I have initialized a local state as follows:

const [myState, setMyState] = useState<IStateType[] | []>([])  

Whenever an item is selected, my approach involves adding it to the useEffect block:

useEffect(() => {
    const result = myState.filter((el) => el.id !== item.id)
    if (isSelected) {
      setMyState([
        ...result,
        {
          propOne: 0,
          propTwo: 1,
          id: item.id,
         ...
        },
      ])
    } else {
      setMyState(result)
    }
  }, [isSelected])

However, incorporating myState in the dependency array of the useEffect function is necessary to include each newly selected item. Yet, doing so unfortunately triggers an infinite loop. How can I successfully update my array with the new selections without causing this issue?

Answer №1

It appears that the issue you are encountering is due to not properly separating the concerns of each component. When relying on previous data every time, the useEffect can become tricky. However, there are two possible solutions to resolve this problem:

Utilize the useState callback function:

The useState function has the capability to be used with a callback instead of a value, as shown below:

    useEffect(() => {
    if (isSelected) {
      setMyState(prevState => [
        ...prevState,
        {
          propOne: 0,
          propTwo: 1,
          id: item.id,
         ...
        },
      ])
    } else {
      setMyState(result)
    }
  }, [isSelected])

Optimal structure for your components + leveraging the useState callback function:

Upon reviewing your approach, it seems like you are attempting to manage both the isSelected for each item and the myState within the same component. While achievable, this practice is suboptimal. Therefore, I would suggest creating two distinct components:

  • <List />: Responsible for managing item selection callbacks and rendering.

<List />:

function List() {
  const [myState, setMyState] = useState([]);

  const isItemSelected = useCallback(
    (itemId) => myState.some((el) => el.id === itemId),
    [myState]
  );

  const handleSelectItem = useCallback(
    (itemId) => {
      const isSelected = isItemSelected(itemId);

      if (isSelected) {
        setMyState((prevState) => prevState.filter((el) => el.id !== itemId));
      } else {
        setMyState((prevState) => prevState.concat({ id: itemId }));
      }
    },
    [isItemSelected]
  );

// Additional implementation here

}
  • <Item />: Tasked with managing the isSelected field internally for each item.

<Item />:

const Item = ({ item, selected = false, onSelectItem }) => {
  const [isSelected, setIsSelected] = useState(false);

// Additional implementation here

};

If desired, you may explore this codesnack that includes a functionality to count renders and assess the efficiency of your solution.

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