我的 state 没有使用 React Hooks 更新

Question

我有一个事件会在更改时触发。 此事件检查哪个过滤器已更改，然后相应地更新 state。

如果我不使用反应钩子，我会选择这样的 -

const target = e.target;
const value = e.type === "checkbox" ? target.checked : target.value;
const name = e.target.name;    
this.setState({ [name]: value });

如您所见，我可以使用[name]更新 state 名称，但由于我使用的是反应挂钩，因此无法使用上述内容。 相反，我得到了这个-

  const [type, setType] = useState("all");
  const [capacity, setCapacity] = useState(1);
  const [price, setPrice] = useState(0);
  const [minPrice, setMinPrice] = useState(0);
  const [maxPrice, setMaxPrice] = useState(0);
  const [minSize, setMinSize] = useState(0);
  const [maxSize, setMaxSize] = useState(0);

  const handleChange = (e) => {
    const target = e.target;
    const value = e.type === "checkbox" ? target.checked : target.value;
    const name = e.target.name;
    
    switch (name) {
      case "type":
        setType(value);
        break;
      case "capacity":
        setCapacity(value);
        break;
      case "price":
        setPrice(value);
        break;
      case "minPrice":
        setMinPrice(value);
        break;
      case "maxPrice":
        setMaxPrice(value);
        break;
      case "minSize":
        setMinSize(value);
        break;
      case "maxSize":
        setMaxSize(value);
        break;
      default:
        return;
    }
  };

您在上面看到的内容由于某种原因不起作用。 当我触发过滤器时，它会进入我已经测试过的情况，但是 state 似乎没有更新。 名称和值也已记录，它们也很好。 我不确定是什么原因造成的，我只是编程新手，所以任何帮助都将不胜感激！

*** 只是重申值和名称都有效，switch 语句也是如此。 只是 state 没有更新 ***

Answer 1

欢迎来到 SO。 您仍然可以编写与使用this.setState提供的 this.setState 示例类似的代码。 这是一个可快速运行的示例。

围绕您的项目的答案：

1. 创建一个使用 useContext 的组件并只加载您需要的值和 handleChange 方法

const Test = () => {
  const { type, capacity, handleChange } = React.useContext(RoomContext);

  console.log(type, capacity);

  return (
      <div>
        <select name="type" onChange={handleChange}>
            <option value="all">all</option>
            <option value="another">another</option>
            <option value="one">one</option>
        </select>
        <select name="capacity" onChange={handleChange}>
          <option value="1">1</option>
          <option value="50">50</option>
          <option value="100">100</option>
        </select>
      </div>
  )
};

2. 将 Test 组件添加为 Room Provider 的子组件。
3. 启动应用程序，您应该会看到它会正常更新

工作可运行示例：

const target = e.target;
const value = e.type === "checkbox" ? target.checked : target.value;
const name = e.target.name;    
this.setState({ [name]: value });

 const rootEl = document.getElementById('root'); const App = () => { const [form, setForm] = React.useState({ name: '', checkbox: false, }); const handleChange = (e) => { const target = e.target; const value = e.type === "checkbox"? target.checked: target.value; const name = e.target.name; setForm(prevState => ({...prevState, [name]: value })); } return ( <div> <label>Name</label> <input type="text" name="name" value={form.name} onChange={handleChange} /> <label>Checkbox</label> <input type="checkbox" name="checkbox" checked={form.checkbox} onChange={handleChange} /> <pre>{JSON.stringify(form)}</pre> </div> ) } ReactDOM.render(<App />, rootEl);

 <script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.13.0/umd/react.production.min.js"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.13.0/umd/react-dom.production.min.js"></script> <div id="root"></div>

这是具有多个 useState 的代码的运行示例。

 const rootEl = document.getElementById('root'); const App = () => { const [name, setName] = React.useState(''); const [checkbox, setCheckbox] = React.useState(false); const handleChange = (e) => { const target = e.target; const value = e.type === "checkbox"? target.checked: target.value; const name = e.target.name; switch (name) { case "name": setName(value); break; case "checkbox": setCheckbox(value); break; default: return; } }; return ( <div> <label>Name</label> <input type="text" name="name" value={name} onChange={handleChange} /> <label>Checkbox</label> <input type="checkbox" name="checkbox" checked={checkbox} onChange={handleChange} /> <pre>{JSON.stringify({ name, checkbox })}</pre> </div> ) } ReactDOM.render(<App />, rootEl);

 <script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.13.0/umd/react.production.min.js"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.13.0/umd/react-dom.production.min.js"></script> <div id="root"></div>

Answer 2

我的问题的解决方法是它没有重新渲染，所以它是整个时间的一个循环。

添加 state 作为 useEffect 中的依赖项可以解决问题，我希望这可以帮助其他遇到类似问题的人。 以一种或另一种方式帮助社区会很棒。

import React, { createContext, useState, useEffect } from "react";

import items from "../data";

export const RoomContext = createContext();

const RoomProvider = (props) => {
  const [rooms, setRooms] = useState([]);
  const [sortedRooms, setSortedRooms] = useState([]);
  const [featuredRooms, setFeaturedRooms] = useState([]);
  const [loading, setLoading] = useState(true);
  const [type, setType] = useState("all");
  const [capacity, setCapacity] = useState(1);
  const [price, setPrice] = useState(0);
  const [minPrice, setMinPrice] = useState(0);
  const [maxPrice, setMaxPrice] = useState(0);
  const [minSize, setMinSize] = useState(0);
  const [maxSize, setMaxSize] = useState(0);
  const [breakfast, setBreakfast] = useState(false);
  const [pets, setPets] = useState(false);

  //call the formatted data
  useEffect(() => {
    //set rooms
    const rooms = formatData(items);
    //set the featured rooms
    const featuredRooms = rooms.filter((room) => room.featured === true);
    //always show the max price as default
    const maxPrice = Math.max(...rooms.map((item) => item.price));
    //always show the max price as default
    const maxSize = Math.max(...rooms.map((item) => item.size));

    setRooms(rooms);
    setSortedRooms(rooms);
    setFeaturedRooms(featuredRooms);
    setLoading(false);
    setMaxPrice(maxPrice);
    setMaxSize(maxSize);
    setPrice(maxPrice);
  }, [
    type,
    capacity,
    price,
    minPrice,
    maxPrice,
    minSize,
    maxSize,
    breakfast,
    pets,
  ]);

  //format data is getting all the required fields we want to pull from the originl data
  const formatData = (items) => {
    let tempItems = items.map((item) => {
      const id = item.sys.id;
      const images = item.fields.images.map((image) => image.fields.file.url);

      const room = { ...item.fields, images: images, id: id };
      return room;
    });
    return tempItems;
  };

  const getRoom = (slug) => {
    let tempRooms = [...rooms];
    const room = tempRooms.find((room) => room.slug === slug);
    return room;
  };

  const handleChange = (e) => {
    const target = e.target;
    const value = e.type === "checkbox" ? target.checked : target.value;
    const name = e.target.name;

    switch (name) {
      case "type":
        setType(value);
        break;
      case "capacity":
        setCapacity(value);
        break;
      case "price":
        setPrice(value);
        break;
      case "minPrice":
        setMinPrice(value);
        break;
      case "maxPrice":
        setMaxPrice(value);
        break;
      case "minSize":
        setMinSize(value);
        break;
      case "maxSize":
        setMaxSize(value);
        break;
      case "breakfast":
        setBreakfast(value);
        break;
      case "pets":
        setPets(value);
        break;
      default:
        return;
    }
    console.log(name, value);
  };

  const filteredRooms = () => {
    let initialRooms = [...rooms];

    if (type !== "all") {
      initialRooms = initialRooms.filter((room) => room.type === type);
    }
    console.log("room type is", type);
    setSortedRooms(initialRooms);
  };

  return (
    <RoomContext.Provider
      value={{
        rooms,
        featuredRooms,
        getRoom,
        loading,
        sortedRooms,
        type,
        capacity,
        price,
        minPrice,
        maxPrice,
        minSize,
        maxSize,
        breakfast,
        pets,
        handleChange,
        filteredRooms,
      }}
    >
      {props.children}
    </RoomContext.Provider>
  );
};

export default RoomProvider;

Answer 3

你导入useState了吗？

import React, {useState} from 'react';