我正在使用 React 构建一个电子商务应用程序,我偶然发现了一个问题,即 React 在首次启动页面时不会根据初始状态呈现 UI。
问题描述:
sort
初始状态为 "latest"
的状态,基于此排序功能 - 如果 sort
值为 "latest"
- 它将首先排序并返回最新的项目。 sort
当前状态。开始时,sort
值已经是 "latest"
. product.js
文件,我已经按字段 createdAt - 1
对带有 mongoose 的项目进行了排序但似乎它不适用于用户界面? -> 什么情况会导致 React 不根据初始状态渲染项目,我们该如何解决?
下面是我的代码:
产品列表.jsx
const ProductList = () => {
const location = useLocation()
const category = location.pathname.split("/")[2]
const [filters, setFilters] = useState({});
const [sort, setSort] = useState("latest");
// For Filters Bar
const handleFilters = (e) => {
const value = e.target.value
// When choosing default value, show all products:
if (value === "") {
return setFilters([])
} else {
setFilters({
...filters,
[e.target.name]: value,
})
}
}
return (
<Container>
<Navbar />
<Announcement />
<Title>Dresses</Title>
<FilterContainer>
<Filter>
<FilterText>Filter Products: </FilterText>
<Select name="color" onChange={handleFilters}>
<Option value="">All Color</Option>
<Option value="white">White</Option>
<Option value="black">Black</Option>
<Option value="brown">Brown</Option>
<Option value="red">Red</Option>
<Option value="blue">Blue</Option>
<Option value="yellow">Yellow</Option>
<Option value="green">Green</Option>
</Select>
<Select name="size" onChange={handleFilters}>
<Option value="">All Size</Option>
<Option>XS</Option>
<Option>S</Option>
<Option>M</Option>
<Option>L</Option>
<Option>XL</Option>
<Option>36</Option>
<Option>37</Option>
<Option>38</Option>
<Option>39</Option>
<Option>40</Option>
<Option>41</Option>
<Option>42</Option>
<Option>43</Option>
</Select>
</Filter>
<Filter>
<FilterText>Sort Products: </FilterText>
<Select onChange={e => setSort(e.target.value)}>
<Option value="latest">Latest</Option>
<Option value="oldest">Oldest</Option>
<Option value="asc">Price ↑ (Low to High)</Option>
<Option value="desc">Price ↓ (High to Low)</Option>
</Select>
</Filter>
</FilterContainer>
<Products category={category} filters={filters} sort={sort} />
<Newsletter />
<Footer />
</Container>
);
}
Products.jsx const Products = ({ category, filters, sort }) => {
const [products, setProducts] = useState([])
const [filteredProducts, setFilteredProducts] = useState([])
useEffect(() => {
const getProducts = async () => {
try {
const res = await axios.get( category
? `http://localhost:5000/api/products?category=${category}`
: `http://localhost:5000/api/products`
)
setProducts(res.data)
} catch (err) {
console.log(`Fetch all items failed - ${err}`)
}
}
getProducts()
}, [category])
useEffect(() => {
category && setFilteredProducts(
products.filter(item =>
Object.entries(filters).every(([key, value]) =>
item[key].includes(value)
)
)
)
}, [category, filters, products])
// Sorting:
useEffect(() => {
console.log(sort)
if (sort === "latest") {
setFilteredProducts(prev =>
[...prev].sort((a, b) => b.createdAt.localeCompare(a.createdAt))
)
} else if (sort === "asc") {
setFilteredProducts(prev =>
[...prev].sort((a, b) => a.price - b.price)
)
} else if (sort === "desc") {
setFilteredProducts(prev =>
[...prev].sort((a, b) => b.price - a.price)
)
} else {
setFilteredProducts(prev =>
[...prev].sort((a, b) => a.createdAt.localeCompare(b.createdAt))
)
}
}, [sort])
return (
<Container>
<Title>Popular In Store</Title>
<ProductsWrapper>
{filteredProducts.map(item => (
<Product key={item._id} item={item} />
))}
</ProductsWrapper>
</Container>
);
}
API 路由 - product.js const router = require('express').Router()
const { verifyTokenAndAdmin } = require('./verifyToken')
const Product = require('../models/Product')
// .... (Other CRUD)
// GET ALL PRODUCTS
router.get("/", async(req, res) => {
const queryNew = req.query.new
const queryCategory = req.query.category
try {
let products = []
if(queryNew) {
products = await Product.find().sort({ createdAt: -1 }).limit(5)
} else if (queryCategory) {
products = await Product.find({
categories: {
$in: [queryCategory],
},
})
} else {
products = await Product.find()
}
res.status(200).json(products)
} catch(err) {
res.status(500).json(`Cannot fetch all products - ${err}`)
}
})
module.exports = router
演示:更新
根据 @idembele70's answer ,我将过滤器的初始状态输入错误为 Array。
name="sort"
在排序选择上。 value="latest"
与 defaultValue="latest"
对于我的排序选择栏 . -> 这使得 最新选项 停止工作,所以我认为它不能在这种情况下使用? 代码
const ProductList = () => {
const location = useLocation()
const category = location.pathname.split("/")[2]
const [filters, setFilters] = useState({});
const [sort, setSort] = useState("latest");
const handleFilters = (e) => {
const value = e.target.value
// When choosing default value, show all products:
if (value === "") {
setFilters({}) // Changed from array to object
} else {
setFilters({
...filters,
[e.target.name]: value,
})
}
}
... <Filter>
<FilterText>Sort Products: </FilterText>
<Select name="sort" onChange={e => setSort(e.target.value)} >
<Option defaultValue="latest">Latest</Option>
<Option value="oldest">Oldest</Option>
<Option value="asc">Price ↑ (Low to High)</Option>
<Option value="desc">Price ↓ (High to Low)</Option>
</Select>
</Filter>
最佳答案
你不应该把改变的products
到状态,因为它使保持更新变得更加复杂,您需要处理各种useEffect
案例。相反,最好定义排序和过滤函数并在渲染时应用它们。这样,您将确保渲染结果始终与数据保持同步:
const filterProducts = (products) => {
if (!category) {
return products;
}
return products.filter(item =>
Object.entries(filters).every(([key, value]) =>
item[key].includes(value),
),
);
};
const sortProducts = (products) => {
switch (sort) {
case "asc":
return [...products].sort((a, b) => a.price - b.price);
case "desc":
return [...products].sort((a, b) => b.price - a.price);
case "latest":
default:
return [...products].sort((a, b) => a.createdAt.localeCompare(b.createdAt));
}
};
return (
<Container>
<Title>Popular In Store</Title>
<ProductsWrapper>
{sortProducts(filterProducts(products)).map(item => (
<Product key={item._id} item={item} />
))}
</ProductsWrapper>
</Container>
);
关于javascript - React 在启动时不显示 UI 的初始状态,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/71793518/