使用 React 中的 useReducer Hook 掌握狀態管理

建立 React 應用程式時，管理狀態可能會變得複雜，尤其是在處理相互依賴的多個狀態變數時。如果您發現自己處於這種情況，那麼是時候探索 useReducer Hook 的強大功能了！

什麼是 useReducer？
useReducer Hook 是一個以可預測的方式管理狀態的強大工具。它允許您以乾淨且有組織的方式管理複雜的狀態邏輯，使您的程式碼更易於維護。

文法
useReducer Hook 接受兩個參數：

useReducer(reducer, initialState)

reducer：包含自訂狀態邏輯的函數。
初始狀態：組件​​的初始狀態，通常是一個物件。

如何運作

1. 目前狀態：基於最新調度操作的目前狀態值。
2. Dispatch Method：一個函數，可以讓你傳送action到reducer來更新狀態

1.範例：
這是如何使用 useReducer Hook 來管理計數器的簡單範例：

import React, { useReducer } from "react";

// Define the initial state
const initialState = { count: 0 };

// Define the reducer function
const reducer = (state, action) => {
  switch (action.type) {
    case "increment":
      return { count: state.count + 1 };
    case "decrement":
      return { count: state.count - 1 };
    default:
      return state;
  }
};

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

  // Inline styles
  const containerStyle = {
    maxWidth: "400px",
    margin: "50px auto",
    padding: "20px",
    borderRadius: "10px",
    boxShadow: "0 4px 20px rgba(0, 0, 0, 0.2)",
    textAlign: "center",
    backgroundColor: "#ffffff",
    fontFamily: "'Roboto', sans-serif",
  };

  const headingStyle = {
    fontSize: "2.5rem",
    margin: "20px 0",
    color: "#333333",
  };

  const buttonStyle = {
    margin: "10px",
    padding: "12px 24px",
    fontSize: "1.1rem",
    border: "none",
    borderRadius: "5px",
    cursor: "pointer",
    transition: "background-color 0.3s, transform 0.3s",
    outline: "none",
    boxShadow: "0 2px 10px rgba(0, 0, 0, 0.1)",
  };

  const incrementButtonStyle = {
    ...buttonStyle,
    backgroundColor: "#28a745",
    color: "white",
  };

  const decrementButtonStyle = {
    ...buttonStyle,
    backgroundColor: "#dc3545",
    color: "white",
  };

  // Hover and active styles
  const buttonHoverStyle = {
    filter: "brightness(1.1)",
    transform: "scale(1.05)",
  };

  return (
    <div style="{containerStyle}">
      <h1 id="Count-state-count">Count: {state.count}</h1>
      <button style="{incrementButtonStyle}" onmouseover="{(e)">
          (e.currentTarget.style = {
            ...incrementButtonStyle,
            ...buttonHoverStyle,
          })
        }
        onMouseOut={(e) => (e.currentTarget.style = incrementButtonStyle)}
        onClick={() => dispatch({ type: "increment" })}
      >
        Increment
      </button>
      <button style="{decrementButtonStyle}" onmouseover="{(e)">
          (e.currentTarget.style = {
            ...decrementButtonStyle,
            ...buttonHoverStyle,
          })
        }
        onMouseOut={(e) => (e.currentTarget.style = decrementButtonStyle)}
        onClick={() => dispatch({ type: "decrement" })}
      >
        Decrement
      </button>
    </div>
  );
}

export default Counter;

輸出：

2.範例：

import React, { useReducer, useState } from "react";

// Define the initial state
const initialState = {
  todos: [],
};

// Define the reducer function
const reducer = (state, action) => {
  switch (action.type) {
    case "ADD_TODO":
      return { ...state, todos: [...state.todos, action.payload] };
    case "REMOVE_TODO":
      return {
        ...state,
        todos: state.todos.filter((todo) => todo.id !== action.payload),
      };
    default:
      return state;
  }
};

function TodoApp() {
  const [state, dispatch] = useReducer(reducer, initialState);
  const [inputValue, setInputValue] = useState("");

  const handleAddTodo = () => {
    if (inputValue.trim()) {
      dispatch({
        type: "ADD_TODO",
        payload: { id: Date.now(), text: inputValue },
      });
      setInputValue(""); // Clear input field
    }
  };

  // Internal CSS
  const styles = {
    container: {
      maxWidth: "600px",
      margin: "50px auto",
      padding: "20px",
      borderRadius: "10px",
      boxShadow: "0 4px 20px rgba(0, 0, 0, 0.1)",
      backgroundColor: "#f9f9f9",
      fontFamily: "'Arial', sans-serif",
    },
    heading: {
      textAlign: "center",
      fontSize: "2.5rem",
      marginBottom: "20px",
      color: "#333",
    },
    input: {
      width: "calc(100% - 50px)",
      padding: "10px",
      borderRadius: "5px",
      border: "1px solid #ccc",
      fontSize: "1rem",
      marginRight: "10px",
    },
    button: {
      padding: "10px 15px",
      fontSize: "1rem",
      border: "none",
      borderRadius: "5px",
      backgroundColor: "#28a745",
      color: "white",
      cursor: "pointer",
      transition: "background-color 0.3s",
    },
    buttonRemove: {
      padding: "5px 10px",
      marginLeft: "10px",
      fontSize: "0.9rem",
      border: "none",
      borderRadius: "5px",
      backgroundColor: "#dc3545",
      color: "white",
      cursor: "pointer",
      transition: "background-color 0.3s",
    },
    todoList: {
      listStyleType: "none",
      padding: 0,
      marginTop: "20px",
    },
    todoItem: {
      display: "flex",
      justifyContent: "space-between",
      alignItems: "center",
      padding: "10px",
      borderBottom: "1px solid #ccc",
      backgroundColor: "#fff",
      borderRadius: "5px",
      marginBottom: "10px",
    },
  };

  return (
    <div style="{styles.container}">
      <h1 id="Todo-List">Todo List</h1>
      <div style="{{" display: justifycontent:>
        <input style="{styles.input}" type="text" value="{inputValue}" onchange="{(e)"> setInputValue(e.target.value)}
          placeholder="Add a new todo"
        />
        <button style="{styles.button}" onclick="{handleAddTodo}">
          Add Todo
        </button>
      </div>
      <ul style="{styles.todoList}">
        {state.todos.map((todo) => (
          <li style="{styles.todoItem}" key="{todo.id}">
            {todo.text}
            <button style="{styles.buttonRemove}" onclick="{()">
                dispatch({ type: "REMOVE_TODO", payload: todo.id })
              }
            >
              Remove
            </button>
          </li>
        ))}
      </ul>
    </div>
  );
}

export default TodoApp;

輸出：

useReducerHook 是 React 工具包的絕佳補充。它使您能夠有效地處理複雜的狀態管理，使您的應用程式更加健壯且更易於維護。在您的下一個專案中嘗試一下，讓您的狀態管理更上一層樓！

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