防止在功能道具更新时重新呈现

Question

我有一个包含几层子组件的表单。表单的状态保持在最高级别，而我向下传递作为更新顶层的道具的函数。唯一的问题是，当表单变得很大（您可以动态添加问题）时，每个单个组件都会在其中一个更新时重新加载。这是我的代码的简化版本（或代码框：https : //codesandbox.io/s/636xwz3rr ）：

const App = () => {
  return <Form />;
}

const initialForm = {
  id: 1,
  sections: [
    {
      ordinal: 1,
      name: "Section Number One",
      questions: [
        { ordinal: 1, text: "Who?", response: "" },
        { ordinal: 2, text: "What?", response: "" },
        { ordinal: 3, text: "Where?", response: "" }
      ]
    },
    {
      ordinal: 2,
      name: "Numero dos",
      questions: [
        { ordinal: 1, text: "Who?", response: "" },
        { ordinal: 2, text: "What?", response: "" },
        { ordinal: 3, text: "Where?", response: "" }
      ]
    }
  ]
};

const Form = () => {
  const [form, setForm] = useState(initialForm);

  const updateSection = (idx, value) => {
    const { sections } = form;
    sections[idx] = value;
    setForm({ ...form, sections });
  };

  return (
    <>
      {form.sections.map((section, idx) => (
        <Section
          key={section.ordinal}
          section={section}
          updateSection={value => updateSection(idx, value)}
        />
      ))}
    </>
  );
};

const Section = props => {
  const { section, updateSection } = props;

  const updateQuestion = (idx, value) => {
    const { questions } = section;
    questions[idx] = value;
    updateSection({ ...section, questions });
  };

  console.log(`Rendered section "${section.name}"`);

  return (
    <>
      <div style={{ fontSize: 18, fontWeight: "bold", margin: "24px 0" }}>
        Section name:
        <input
          type="text"
          value={section.name}
          onChange={e => updateSection({ ...section, name: e.target.value })}
        />
      </div>
      <div style={{ marginLeft: 36 }}>
        {section.questions.map((question, idx) => (
          <Question
            key={question.ordinal}
            question={question}
            updateQuestion={v => updateQuestion(idx, v)}
          />
        ))}
      </div>
    </>
  );
};

const Question = props => {
  const { question, updateQuestion } = props;

  console.log(`Rendered question #${question.ordinal}`);

  return (
    <>
      <div>{question.text}</div>
      <input
        type="text"
        value={question.response}
        onChange={e =>
          updateQuestion({ ...question, response: e.target.value })
        }
      />
    </>
  );
};

我已经尝试过使用useMemo和useCallback，但是我不知道如何使它工作。问题是传递函数以更新其父级。我无法弄清楚如何在每次表单更新时不对其进行更新。

我无法在任何地方在线找到解决方案。也许我在寻找错误的东西。感谢您提供的任何帮助！

解

使用Andrii-Golubenko的答案和本文以及React.memo，useCallback和useReducer的React优化，我能够提出以下解决方案：https : //codesandbox.io/s/myrjqrjm18

请注意，控制台日志仅显示重新呈现已更改组件的方式。

Answer 1

1. Use React feature React.memo for functional components to prevent re-render if props not changed, similarly to PureComponent for class components.
2. When you pass callback like that:

<Section
    ...
    updateSection={value => updateSection(idx, value)}
/>

your component Section will rerender each time when parent component rerender, even if other props are not changed and you use React.memo. Because your callback will re-create each time when parent component renders. You should wrap your callback in useCallback hook.

3. Using useState is not a good decision if you need to store complex object like initialForm. It is better to use useReducer;

Here you could see working solution: https://codesandbox.io/s/o10p05m2vz