Question

TypeError：从 API 获取时无法读取未定义的属性“map”

2021-04-19

348

javascript reactjs array.prototype.map

我一直在尝试进行简单的 API 提取，但我不明白我做错了什么我读过很多问题，但我真的觉得我错过了一些东西，因为一切似乎都是正确的（显然不是）

import { useState } from "react";
import ProductCard from "./ArticleCard/ProductCard.js";

export default function ProductsIndex() {
  const [searchText, set_searchText] = useState("");
  const [state, set_state] = useState({ status: "idle" });
  const search = async () => {
    if (searchText === "") {
      set_state({ status: "idle" });
      return;
    }
    set_state({ status: "searching" });
    const queryParam = encodeURIComponent(searchText);
    const data = await fetch(
      /* base browser fetch  https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API/Using_Fetch*/
      `https://omdbapi.com/?apikey=6a06f383&s=${queryParam}`
    ).then((r) => r.json());
    set_state({ status: "done!", data: data.Search });
  };
  console.log(state.data);
  return (
    <div className="ProductsIndex">
      We sell movies for a high price.
      <h1>Discover some movies!</h1>
      <p>
        <input
          value={searchText}
          onChange={(e) => set_searchText(e.target.value)}
        />
        <button onClick={search}>Search</button>
      </p>{" "}
      <p>
        {state.data.map((movie) => (
          <ProductCard
            poster={movie.poster}
            title={movie.title}
            year={movie.year}
            type={movie.type}
          />
        ))}
      </p>
    </div>
  );
}

console.log(state.data) 给出了所需的结果，所以就好像数据没有被传递下去一样......我不明白为什么

console.log(state.data) 的结果：

[
    {
        "Title": "Finding Nemo",
        "Year": "2003",
        "imdbID": "tt0266543",
        "Type": "movie",
        "Poster": "https://m.media-amazon.com/images/M/MV5BZTAzNWZlNmUtZDEzYi00ZjA5LWIwYjEtZGM1NWE1MjE4YWRhXkEyXkFqcGdeQXVyNjU0OTQ0OTY@._V1_SX300.jpg"
    },
    {
        "Title": "Finding Nemo",
        "Year": "2003",
        "imdbID": "tt0401422",
        "Type": "game",
        "Poster": "https://m.media-amazon.com/images/M/MV5BNGEzMjdiZGEtYzU3ZC00OGFmLWI3NTgtZTcyNTFjYTliNDg5XkEyXkFqcGdeQXVyNjExODE1MDc@._V1_SX300.jpg"
    },
    {
        "Title": "Finding Nemo Submarine Voyage",
        "Year": "2007",
        "imdbID": "tt1319713",
        "Type": "movie",
        "Poster": "https://m.media-amazon.com/images/M/MV5BMzAxMzMyODQtNWY0Yy00N2M3LWE5MDQtZDUzNjc1ZGFmMzA4XkEyXkFqcGdeQXVyMzkxMzc4Mw@@._V1_SX300.jpg"
    },
    {
        "Title": "Finding Nemo: Studio Tour of Pixar",
        "Year": "2003",
        "imdbID": "tt1248974",
        "Type": "movie",
        "Poster": "N/A"
    },
    {
        "Title": "Finding Nemo: A Filmmakers' Roundtable",
        "Year": "2012",
        "imdbID": "tt10255922",
        "Type": "movie",
        "Poster": "https://m.media-amazon.com/images/M/MV5BNjAyMTBmODQtZGYxMC00NjdhLThhN2MtODlhMDI4NTczYTMyXkEyXkFqcGdeQXVyNDEyNjEzOTg@._V1_SX300.jpg"
    }
]

谢谢你的帮助

Answer 1

我刚刚修复了几件事：

定义数据的状态

const [state, set_state] = useState({ status: "idle",data:[] });

在迭代之前检查数组

{state.data && state.data.map((movie) => (
<ProductCard
poster={movie.poster}
title={movie.title}
year={movie.year}
type={movie.type}
/>
))}

我创建了一个小演示：搜索 nemo，按下按钮，请检查控制台， https://codesandbox.io/s/flamboyant-dubinsky-3bxsf?file=/src/App.js:155-219

Answer 2

您应该初始化 state.data 请尝试这样做。

 const [state, set_state] = useState({ status: "idle",data:[] });

Answer 3

我想我知道问题出在哪里了！！！当您设置新状态时，它会替换前一个状态。考虑到这一点，当您像这样设置加载状态时：

set_state({ status: "idle" });

它实际上使您的 state.data 未定义，因此它会引发异常。

不要重新分配整个状态，而是尝试仅替换需要更改的内容：

set_state({ ...state, status: "idle" });

因此，每当您调用 set_state 方法时，您都应该添加 ...state ，这样您就不会遇到此问题。