状态变量未使用反应钩子更新

Question

I am learning ReactJS and trying to update the parent props with the updated state of ingredients from the child component. The setUserIngredients is called and updated ingredients are being passed to parent.

Code :

const [userIngredients, setUserIngredients] = useState([]);

const removeIngredientHandler = id => {
    setLoading(true);
    fetch(`https://***************.com/ingredients/${id}.json`,{
      method:'DELETE'
    }).then(response=>{
      setLoading(false);
      setUserIngredients(prevIngredients => 
        prevIngredients.filter(ingredient =>{
          return (ingredient.id !== id)
           //return  ingredient;
        })
      );
      **props.ingredients(userIngredients);**
      //userIngredients is still having old value 
      //need to check on this
    }).catch(error => {
      setError(error.message);
    })
  };

Answer 1

The problem is that userIngredients is a variable that is created when the component renders, set to a version fo the state when that component renders. And when you start an asynchronous operation (like a fetch) the callback you pass to that operation will be bound the values from when that callback was created.

The fix here is pretty simple. In the spot where you calculate your new ingredients, simply execute whatever callback you need before returning the value to be stored in the state.

Something like:

fetch(`https://***************.com/ingredients/${id}.json`, {
  method: 'DELETE',
}).then(response => {
  setLoading(false)
  setUserIngredients(prevIngredients => {
    // Figure out the new ingredients
    const newIngredients = prevIngredients.filter(ingredient => ingredient.id !== id)

    // Call your callback with the new ingredients
    props.ingredients(newIngredients)

    // Return the new ingredients to be stored in your state
    return newIngredients
  })
})