useReducer 以及它与 useState 的不同之处-js教程-PHP中文网

useReducer and how it is different from useState

介绍

React 提供了两个用于管理状态的关键钩子：useState 和 useReducer。虽然两者都旨在处理功能组件中的状态，但它们用于不同的场景。本文探讨了两者之间的差异，并重点介绍了何时应该使用它们，并提供了示例以便更好地理解

何时使用 useState

useState 是一个简单而有效的钩子，用于在以下情况下处理本地状态：

您需要管理简单的状态（例如布尔值、数字或字符串）。
您希望通过最少的设置直接更新状态。
状态没有复杂的转换或对多个变量的依赖。

基本语法

const [state, setState] = useState(initialState);

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状态：当前状态。
setState：更新状态的函数。
initialState：初始状态

何时使用 useReducer

useReducer 在以下情况下很有用：

你有复杂的状态逻辑。
多个状态更新相互依赖。

基本语法

const [state, dispatch] = useReducer(reducer, initialState);

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状态：当前状态。
dispatch：向reducer发送动作以触发状态更新的函数。
reducer：reducer 是一个纯函数，它接受两个参数：当前状态和操作。它根据操作返回新状态。

基本语法

const reducer = (state, action) => {
    switch (action.type) {
        case 'INCREMENT':
            return { count: state.count + 1 };
        case 'DECREMENT':
            return { count: state.count - 1 };
        default:
            return state;
    }
}

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动作：动作是一个描述应该发生什么变化的对象
它通常具有 type 属性和可选的 payload.
类型告诉reducer要进行什么样的状态改变。
有效负载携带更改所需的任何附加数据。
InitialState：初始状态，就像useState中的initialstate一样。

示例 1 带有 useState 的计数器应用程序

const [state, setState] = useState(initialState);

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解释

我们使用 useState 来跟踪计数值。
我们有两个按钮：一个用于增加计数状态，一个用于减少计数状态。
直接使用setCount函数更新状态。

示例 2：带有 useReducer 的计数器应用程序

const [state, dispatch] = useReducer(reducer, initialState);

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解释

reducer 函数控制状态应如何根据分派的操作进行更改。
我们不直接设置状态，而是调度操作（递增、递减）来触发更改。

示例 3：使用 useReducer 处理表单输入

让我们将概念扩展到处理具有多个输入字段的表单。此场景非常适合 useReducer，因为它根据操作更新多个状态属性。

const reducer = (state, action) => {
    switch (action.type) {
        case 'INCREMENT':
            return { count: state.count + 1 };
        case 'DECREMENT':
            return { count: state.count - 1 };
        default:
            return state;
    }
}

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解释

reducer 通过根据操作的类型更新不同的属性（姓名、电子邮件）来管理表单状态。
Dispatch 将操作发送到reducer 以更新状态。有效负载携带数据（例如输入值）。

示例 4：使用 useReducer 构建测验应用程序

注意：样式是用 tailwindcss 完成的

import React, { useState } from 'react';

export default function Counter() {
  const [count, setCount] = useState(0);

  return (
    <div>
      <p>Count: {count}</p>
      <button onClick={() => setCount(count + 1)}>Increment</button>
      <button onClick={() => setCount(count - 1)}>Decrement</button>
    </div>
  );
}

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解释

*useReducer 的初始状态

import React, { useReducer } from 'react';

function reducer(state, action) {
  switch (action.type) {
    case 'increment':
      return { count: state.count + 1 };
    case 'decrement':
      return { count: state.count - 1 };
    default:
      return state;
  }
}

export default function Counter() {
  const [state, dispatch] = useReducer(reducer, { count: 0 });

  return (
    <div>
      <p>Count: {state.count}</p>
      <button onClick={() => dispatch({ type: 'increment' })}>Increment</button>
      <button onClick={() => dispatch({ type: 'decrement' })}>Decrement</button>
    </div>
  );
}

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减速机功能

import React, { useReducer } from 'react';

const initialState = {
  name: '',
  email: ''
};

function reducer(state, action) {
  switch (action.type) {
    case 'setName':
      return { ...state, name: action.payload };
    case 'setEmail':
      return { ...state, email: action.payload };
    default:
      return state;
  }
}

export default function Form() {
  const [state, dispatch] = useReducer(reducer, initialState);

  return (
    <div>
      <input
        type="text"
        value={state.name}
        onChange={(e) => dispatch({ type: 'setName', payload: e.target.value })}
        placeholder="Name"
      />
      <input
        type="email"
        value={state.email}
        onChange={(e) => dispatch({ type: 'setEmail', payload: e.target.value })}
        placeholder="Email"
      />
      <p>Name: {state.name}</p>
      <p>Email: {state.email}</p>
    </div>
  );
}

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减速器处理三个动作：

SELECT_OPTION：当用户选择答案时
NEXT_QUESTION：转到下一个问题时
RESTART：重新开始测验时

造型逻辑

import React, { useReducer } from 'react';

// Quiz data with detailed explanations
const quizData = [
  {
    question: "What hook is used to handle complex state logic in React?",
    options: ["useState", "useReducer", "useEffect", "useContext"],
    correct: 1,
    explanation: "useReducer is specifically designed for complex state management scenarios."
  },
  {
    question: "Which function updates the state in useReducer?",
    options: ["setState", "dispatch", "update", "setReducer"],
    correct: 1,
    explanation: "dispatch is the function provided by useReducer to trigger state updates."
  },
  {
    question: "What pattern is useReducer based on?",
    options: ["Observer Pattern", "Redux Pattern", "Factory Pattern", "Module Pattern"],
    correct: 1,
    explanation: "useReducer is inspired by Redux's state management pattern."
  }
];

// Initial state with feedback state added
const initialState = {
  currentQuestion: 0,
  score: 0,
  showScore: false,
  selectedOption: null,
  showFeedback: false, // New state for showing answer feedback
};

// Enhanced reducer with feedback handling
const reducer = (state, action) => {
  switch (action.type) {
    case 'SELECT_OPTION':
      return {
        ...state,
        selectedOption: action.payload,
        showFeedback: true, // Show feedback when option is selected
      };
    case 'NEXT_QUESTION':
      const isCorrect = action.payload === quizData[state.currentQuestion].correct;
      const nextQuestion = state.currentQuestion + 1;
      return {
        ...state,
        score: isCorrect ? state.score + 1 : state.score,
        currentQuestion: nextQuestion,
        showScore: nextQuestion === quizData.length,
        selectedOption: null,
        showFeedback: false, // Reset feedback for next question
      };
    case 'RESTART':
      return initialState;
    default:
      return state;
  }
};

const Quiz = () => {
  const [state, dispatch] = useReducer(reducer, initialState);
  const { currentQuestion, score, showScore, selectedOption, showFeedback } = state;

  const handleOptionClick = (optionIndex) => {
    dispatch({ type: 'SELECT_OPTION', payload: optionIndex });
  };

  const handleNext = () => {
    if (selectedOption !== null) {
      dispatch({ type: 'NEXT_QUESTION', payload: selectedOption });
    }
  };

  const handleRestart = () => {
    dispatch({ type: 'RESTART' });
  };

  if (showScore) {
    return (
      <div className="flex flex-col items-center justify-center min-h-screen bg-gray-100 p-4">
        <div className="bg-white rounded-lg shadow-lg p-8 max-w-md w-full">
          <h2 className="text-2xl font-bold text-center mb-4">Quiz Complete!</h2>
          <p className="text-xl text-center mb-6">
            Your score: {score} out of {quizData.length}
          </p>
          <button
            onClick={handleRestart}
            className="w-full bg-blue-500 text-white py-2 px-4 rounded hover:bg-blue-600 transition-colors"
          >
            Restart Quiz
          </button>
        </div>
      </div>
    );
  }

  const currentQuizData = quizData[currentQuestion];
  const isCorrectAnswer = (optionIndex) => optionIndex === currentQuizData.correct;

  return (
    <div className="flex flex-col items-center justify-center min-h-screen bg-gray-100 p-4">
      <div className="bg-white rounded-lg shadow-lg p-8 max-w-md w-full">
        <div className="mb-6">
          <p className="text-sm text-gray-500 mb-2">
            Question {currentQuestion + 1}/{quizData.length}
          </p>
          <h2 className="text-xl font-semibold mb-4">{currentQuizData.question}</h2>
        </div>

        <div className="space-y-3 mb-6">
          {currentQuizData.options.map((option, index) => {
            let buttonStyle = 'bg-gray-50 hover:bg-gray-100';

            if (showFeedback && selectedOption === index) {
              buttonStyle = isCorrectAnswer(index) 
                ? 'bg-green-100 border-2 border-green-500 text-green-700'
                : 'bg-red-100 border-2 border-red-500 text-red-700';
            }

            return (
              <button
                key={index}
                onClick={() => handleOptionClick(index)}
                disabled={showFeedback}
                className={`w-full p-3 text-left rounded-lg transition-colors ${buttonStyle}`}
              >
                {option}
              </button>
            );
          })}
        </div>

        {showFeedback && (
          <div className={`p-4 rounded-lg mb-4 ${
            isCorrectAnswer(selectedOption)
              ? 'bg-green-50 text-green-800'
              : 'bg-red-50 text-red-800'
          }`}>
            {isCorrectAnswer(selectedOption)
              ? "Correct! "
              : `Incorrect. The correct answer was: ${currentQuizData.options[currentQuizData.correct]}. `}
            {currentQuizData.explanation}
          </div>
        )}

        <button
          onClick={handleNext}
          disabled={!showFeedback}
          className={`w-full py-2 px-4 rounded transition-colors ${
            !showFeedback
              ? 'bg-gray-300 cursor-not-allowed'
              : 'bg-blue-500 text-white hover:bg-blue-600'
          }`}
        >
          Next Question
        </button>
      </div>
    </div>
  );
};

export default Quiz;

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此代码确定按钮样式：

默认：灰色背景
正确答案：绿色背景，绿色边框
错误答案：红色背景，红色边框

反馈显示

// Initial state
const initialState = {
  currentQuestion: 0,
  score: 0,
  showScore: false,
  selectedOption: null,
  showFeedback: false, // New state for feedback
};

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这显示了选择答案后的反馈：

*显示答案是否正确
*如果错误则显示正确答案
*包括解释

测验应用程序的托管链接

测验技术写作.vercel.app

useState 和 useReducer 的比较

Feature	useState	useReducer
Best for	Simple state	Complex state logic
State Management	Direct, using setState	Managed through a reducer function
Boilerplate Code	Minimal	Requires more setup
State Update	Inline with setState	Managed by dispatch and reducer