使用 useReducer 持久化 localStorage

Persist localStorage with useReducer

我有一个使用 useState 的迷你购物车应用程序。我现在想重构应用程序的状态以由 useReducer 管理并继续使用 localStorage.

持久化数据

我在弄清楚如何重构时遇到了麻烦,因为涉及到许多移动的部分。我如何着手重构 addToCartHandler 中的逻辑以代替在 ADD_TO_CART 案例中使用?从那里,我相信我能够找出 cartReducer 中其他案例的模式。谢谢。

https://codesandbox.io/s/goofy-water-pb903?file=/src/App.js

这是我的工作。我添加了 cartReducer 的所有案例,因为我玩得很开心。

如果您想自己完成,这里是第一个使用 localStorage 来保存项目值的设置案例。

我所做的概述是:使用 switch case 在 reducer 中设置新状态,然后每次购物车通过效果更改时将 localStorage 状态设置为新值。

产品中的逻辑只是被一个简单的动作调度所取代。因为逻辑在减速器中。您可能可以简化 ADD_TO_CART 案例中的逻辑,但这会以不可变的方式处理所有事情。使用像 immer 这样的东西可以大大简化逻辑。

const storageKey = "localCart";
const cartReducer = (state, action) => {
  switch (action.type) {
    case "ADD_TO_CART": {
      const product = action.payload;
      let index = state.findIndex((item) => product.name === item.name);
      if (index >= 0) {
        const newState = [...state];
        newState.splice(index, 1, {
          ...state[index],
          quantity: state[index].quantity + 1
        });
        return newState
      } else {
        return [...state, { ...product, quantity: 1 }];
      }
    }
    default:
      throw new Error();
  }
};

App组件中使用:

  const [cart, cartDispatch] = useReducer(
    cartReducer,
    [],
    // So we only have to pull from localStorage one time - Less file IO
    (initial) => JSON.parse(localStorage.getItem(storageKey)) || initial
  );
  useEffect(() => {
    // This is a side-effect and belongs in an effect
    localStorage.setItem(storageKey, JSON.stringify(cart));
  }, [cart]);

Product组件中使用:

  const addToCartHandler = (product) => {
    dispatch({ type: "ADD_TO_CART", payload: product });
  };

全职工作CodeSandbox

使用上下文 API 管理购物车状态

我首先将您的购物车状态和对本地存储的持久性隔离到反应上下文提供程序。上下文可以为应用程序的其余部分提供购物车状态和操作调度程序,并在使用效果更新状态时将状态持久保存到 localStorage。这将所有状态管理与应用程序分离,应用程序只需要使用上下文来访问购物车状态并调度操作来更新它。

import React, { createContext, useEffect, useReducer } from "react";
import { cartReducer, initializer } from "../cartReducer";

export const CartContext = createContext();

export const CartProvider = ({ children }) => {
  const [cart, dispatch] = useReducer(cartReducer, [], initializer);

  useEffect(() => {
    localStorage.setItem("localCart", JSON.stringify(cart));
  }, [cart]);

  return (
    <CartContext.Provider
      value={{
        cart,
        dispatch
      }}
    >
      {children}
    </CartContext.Provider>
  );
};

将应用包装在 index.js

中的 CartProvider
<CartProvider>
  <App />
</CartProvider>

完善应用程序的其余部分

cartReducer中细化reducer,导出初始化函数和action creators。

const initialState = [];

export const initializer = (initialValue = initialState) =>
  JSON.parse(localStorage.getItem("localCart")) || initialValue;

export const cartReducer = (state, action) => {
  switch (action.type) {
    case "ADD_TO_CART":
      return state.find((item) => item.name === action.item.name)
        ? state.map((item) =>
            item.name === action.item.name
              ? {
                  ...item,
                  quantity: item.quantity + 1
                }
              : item
          )
        : [...state, { ...action.item, quantity: 1 }];

    case "REMOVE_FROM_CART":
      return state.filter((item) => item.name !== action.item.name);

    case "DECREMENT_QUANTITY":
      // if quantity is 1 remove from cart, otherwise decrement quantity
      return state.find((item) => item.name === action.item.name)?.quantity ===
        1
        ? state.filter((item) => item.name !== action.item.name)
        : state.map((item) =>
            item.name === action.item.name
              ? {
                  ...item,
                  quantity: item.quantity - 1
                }
              : item
          );

    case "CLEAR_CART":
      return initialState;

    default:
      return state;
  }
};

export const addToCart = (item) => ({
  type: "ADD_TO_CART",
  item
});

export const decrementItemQuantity = (item) => ({
  type: "DECREMENT_QUANTITY",
  item
});

export const removeFromCart = (item) => ({
  type: "REMOVE_FROM_CART",
  item
});

export const clearCart = () => ({
  type: "CLEAR_CART"
});

Product.js 中通过 useContext 挂钩获取购物车上下文并调度 addToCart 操作

import React, { useContext, useState } from "react";
import { CartContext } from "../CartProvider";
import { addToCart } from "../cartReducer";

const Item = () => {
  const { dispatch } = useContext(CartContext);

  ...

  const addToCartHandler = (product) => {
    dispatch(addToCart(product));
  };

  ...

  return (
    ...
  );
};

CartItem.js 获取并使用购物车上下文来调度操作以减少数量或删除项目。

import React, { useContext } from "react";
import { CartContext } from "../CartProvider";
import { decrementItemQuantity, removeFromCart } from "../cartReducer";

const CartItem = () => {
  const { cart, dispatch } = useContext(CartContext);

  const removeFromCartHandler = (itemToRemove) =>
    dispatch(removeFromCart(itemToRemove));

  const decrementQuantity = (item) => dispatch(decrementItemQuantity(item));

  return (
    <>
      {cart.map((item, idx) => (
        <div className="cartItem" key={idx}>
          <h3>{item.name}</h3>
          <h5>
            Quantity: {item.quantity}{" "}
            <span>
              <button type="button" onClick={() => decrementQuantity(item)}>
                <i>Decrement</i>
              </button>
            </span>
          </h5>
          <h5>Cost: {item.cost} </h5>
          <button onClick={() => removeFromCartHandler(item)}>Remove</button>
        </div>
      ))}
    </>
  );
};

App.js 通过上下文挂钩获取购物车状态和调度程序,并更新总项目和价格逻辑以说明项目数量。

import { CartContext } from "./CartProvider";
import { clearCart } from "./cartReducer";

export default function App() {
  const { cart, dispatch } = useContext(CartContext);

  const clearCartHandler = () => {
    dispatch(clearCart());
  };

  const { items, total } = cart.reduce(
    ({ items, total }, { cost, quantity }) => ({
      items: items + quantity,
      total: total + quantity * cost
    }),
    { items: 0, total: 0 }
  );

  return (
    <div className="App">
      <h1>Emoji Store</h1>
      <div className="products">
        <Product />
      </div>
      <div className="cart">
        <CartItem />
      </div>
      <h3>
        Items in Cart: {items} | Total Cost: ${total.toFixed(2)}
      </h3>
      <button onClick={clearCartHandler}>Clear Cart</button>
    </div>
  );
}