什么时候在REACT中使用构造函数合适？ [英] When is it appropriate to use a constructor in REACT?

问题描述

我了解OOP语言（例如C ++）中的构造函数的概念。但是，我不完全确定何时在REACT中使用构造函数。我确实知道JavaScript是面向对象的，但是我不确定构造函数实际上是在构造。

I understand the concept of constructors in OOP languages like C++. However, I am not entirely sure when to use a constructor in REACT. I do understand that JavaScript is object oriented, but I am not sure what the constructor is actually 'constructing'.

在渲染子组件时，是否需要在子组件？例如：

When rendering a child component, do you need a constructor in the child component? For example:

class App extends React.Component {
   constructor(props) {
      super(props);
      this.state = {
         items: [],
         error: null
      }
    }
    render () {
       return (
          <React.Fragment>
             <ChildComponent data={this.state.items}></ChildComponent>
          </React.Fragment>
       )
    }
}

为了简洁起见，我将简短示例。但是，为什么需要构造函数？

I will keep the example short for the sake of brevity. But, why would do you need a constructor? And would you need a constructor in the child component for props?

很有可能我的ES6知识还不够。

It is possible that my ES6 knowledge is not up to snuff.

推荐答案

如果您不初始化状态并且不绑定方法，则无需为React组件实现构造函数。

React组件的构造函数在挂载之前被调用。为React.Component子类实现构造函数时，应在其他任何语句之前调用super（props）。否则，在构造函数中将无法定义this.props，这可能会导致错误。

The constructor for a React component is called before it is mounted. When implementing the constructor for a React.Component subclass, you should call super(props) before any other statement. Otherwise, this.props will be undefined in the constructor, which can lead to bugs.

通常，在React构造器中仅用于两个目的：

Typically, in React constructors are only used for two purposes:

• 通过向this.state分配对象来初始化本地状态。


• 将事件处理程序方法绑定到实例。

https://reactjs.org/docs/react-component.html#constructor

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