javascript - react 备忘录没有得到 Prop

Question

React 备忘录没有捕获 Prop ，prevProps也不是 nextProps并且组件渲染良好。 react 文档说

如果你的函数组件在给定相同的 props 的情况下呈现相同的结果，你可以将它包装在对 React.memo 的调用中以提高性能。

我的问题是使用 react 备忘录停止两次渲染，但备忘录似乎不起作用，并且组件使用相同的 Prop 渲染两次。

组件在 Create New Event 时呈现点击 /events
here is the live sandbox .

子组件位于 /components/Event/CreateEvent/CreateEvent.js

父组件位于 /Pages/Event/Event.js行号999 ' 从哪里触发子组件

这是代码:

import React from "react";
import AuthContext from "../../context/global-context";
import CreateEvent from "../../components/Event/CreateEvent/CreateEvent";

function Events({ location }) {

  // Sate Managing
  const [allEvents, setAllEvents] = React.useState([]);
  const [creating, setCreating] = React.useState(false);

  // Context As State
  const { token, email } = React.useContext(AuthContext);

  // Creating Event Showing
  const modelBoxHandler = () => {
    // works on when the ViewEvent is open
    if (eventSelected) {
      setEventSelected(null);
      return;
    }

    setCreating(!creating);
  };

  return (
    <div className="events">

      {/* New Event Creating */}
      {creating && (
        <CreateEvent onHidder={modelBoxHandler} allEvents={allEvents} />
      )}

      {console.log("Event Rendered.js =>")}

    </div>
  );
}

export default React.memo(Events, () => true);

矩形备忘录没有 Prop 的子组件:

import React from "react";
import AuthContext from "../../../context/global-context";

function CreateEvent({ onHidder, allEvents }) {
  // Context
  const { token } = React.useContext(AuthContext);

  console.log("CreatedEvent.js REnder");
  return (
       ... Some code here
  );
}

export default React.memo(CreateEvent, (prevProps, nextProps) => {
  console.log("Hello", prevProps, nextProps);
});

提前感谢您的宝贵答案和时间!

Answer 1

问题是基于 creating变量你实际上是重新安装而不渲染 CreateEvent 组件。这意味着如果创建变量更改，则组件在创建为真时被卸载并重新安装，因此它不是重新渲染

您还必须注意 modelBoxHandler函数引用也会在每次重新渲染时发生变化，因此即使您的 CreateEvent 组件处于渲染状态并且父级由于某种原因重新渲染，CreateEvent 组件也将重新渲染

您需要进行 2 项更改才能使其更好地工作

使用 useCallback 钩子(Hook)定义 modelBoxHandler

在 createEvent 中根据创建属性

进行条件渲染

 // Creating Event Showing
  const modelBoxHandler = useCallback(() => {
    // works on when the ViewEvent is open
    if (eventSelected) {
      setEventSelected(null);
      return;
    }

    setCreating(prevCreating => !prevCreating);
  }, [eventSelected]);
   ...
    return (
        <div className="events">

          {/* New Event Creating */}
          <CreateEvent creating={creating} onHidder={modelBoxHandler} allEvents={allEvents} />

          {console.log("Event Rendered.js =>")}

        </div>
    );

并在 createEvent

function CreateEvent({ onHidder, allEvents, creating }) {
  // Context
  const { token } = React.useContext(AuthContext);

  console.log("CreatedEvent.js REnder");
  if(!creating) {
     return null;
  }
  return (
       ... Some code here
  );
}

export default React.memo(CreateEvent);