React Hooks 和 useState 的使用

React Hooks and the use of useState(React Hooks 和 useState 的使用)

问题描述

我有一个包含一些状态的组件.有什么区别

I have a component with some states. What is the different between

示例 1:

function CompA() {
  [a, setA] = useState(0);
  [b, setB] = useState("Test");
  return (<div>{{ a }} and {{ b }}</div>);
}

和示例 2:

function CompA() {
  [state, setState] = useState({a: 0, b: "Test"});
  return (<div>{{ state.a }} and {{ state.b }}</div>);
}

示例 2 更详细.但是我在网上看到的所有 hooks 示例都更喜欢示例 2 的风格.是否有任何性能损失或最佳实践偏爱一种或另一种?

Example 2 is more verbose. But all the hooks example I see on the internet prefer the Example 2's style. Is there any performance penalty or best practice that preferred one or another??

推荐答案

这两种方法的最终目标相同，您将创建一个呈现以下元素的组件:<div>{{ state.a }} 和 {{ state.b }}</div>

Both approaches will end up with the same end goal, whereby you will create a component that renders the following element: <div>{{ state.a }} and {{ state.b }}</div>

但是，这是示例 1 的场景.如果您希望同时更新两个状态(a 和 b)，则必须调用 2 种不同的方法来更新状态:

However, here's a scenario for Example 1. If you wish to update both states(a, and b) , you will have to call 2 different methods to update the state:

setA(1);
setB('bbbb');

另一方面，对于示例 2，您只需调用 1 个方法即可更新状态.

On the other hand, for Example 2, you will only need to call 1 method to update the state.

setState({
  a: 1,
  b: 'bbb',
});

但是，这种方法的缺点是，如果您只想更新其中一个属性，则必须传播整个状态对象(归功于 @DrewReese 指出这一点).例如，如果您只想更新 b，

However, the downside of this approach is that, you will have to spread the entire state object if you only wish to update only one of the properties (credit goes to @DrewReese for pointing this out). For instance, if you want to update only b,

setState({
  ...state, 
  b: 'bbb',
});

话虽如此，说示例 1 的性能"较差是不准确的，因为如果在同一个事件处理程序中调用更新，React 会批量更新，并导致一次重新渲染.

That being said, it will not be accurate to state that Example 1 is less "performant", as React will batch the updates if they are called within the same event handler, and cause a single re-render.

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