useMemo函数在渲染过程中运行

Question

基本上，我要做的是在代码的一部分中调用这个'myMemoFunction'函数。问题是，根据我在文档中读到的内容，useMemo()在渲染时立即执行此函数，因此myArray参数仍然为空。然后返回下面的错误。

const myMemoFunction = useMemo((myArray) => {
const users = myArray.map((a) => a.user)
return users;
})

错误：

myArray未定义

Answer 1

在这种情况下应该使用useCallback因为CCD_ 5存储变量。我也怀疑这是否需要争论。

编辑：

const myMemoFunction = useCallback((myArray) => {
// this won't be called on renders
const users = myArray.map((a) => a.user)
return users;
}, [] /* dont forget the dependency you want to evaluate only once */)
// later
myMemoFunction(arr);

使用编辑2备注：

const myMemoVariable = useMemo(() => {
// re-evaluates each time myArray changes
const users = myArray.map((a) => a.user)
return users;
}, [myArray])
// note that we dont use myMemoVariable() to get our variable
console.log(myMemoVariable)

Answer 2

将您的代码更新到此

const myMemoFunction = useMemo((myArray) => {
// myArray could be undefined, that was why ? was added
const users = myArray?.map((a) => a.user)
return users;
}, [myArray]) // myArray is in a dependency of the function

您的备忘录功能将使用新的myArray变量进行更新

将myArray变量初始化为数组总是很好的，例如[]