构建 React 应用程序时，管理状态可能会变得复杂，尤其是在处理相互依赖的多个状态变量时。如果您发现自己处于这种情况，那么是时候探索 useReducer Hook 的强大功能了！
什么是 useReducer？
useReducer Hook 是一个以可预测的方式管理状态的强大工具。它允许您以干净且有组织的方式管理复杂的状态逻辑，使您的代码更易于维护。
语法
useReducer Hook 接受两个参数：
useReducer(reducer, initialState)
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reducer：包含自定义状态逻辑的函数。
初始状态：组件的初始状态，通常是一个对象。
如何运作
- 当前状态：基于最新调度操作的当前状态值。
- Dispatch Method：一个函数，可以让你向reducer发送action来更新状态
1.示例：
这是如何使用 useReducer Hook 来管理计数器的简单示例：
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 style={headingStyle}>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;
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输出：
2.示例：
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 style={styles.heading}>Todo List</h1>
<div style={{ display: "flex", justifyContent: "center" }}>
<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;
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输出：
useReducerHook 是 React 工具包的绝佳补充。它使您能够有效地处理复杂的状态管理，使您的应用程序更加健壮且更易于维护。在您的下一个项目中尝试一下，让您的状态管理更上一层楼！
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