TypeError: Cannot read property 'map' of undefined while fetching from API

Question

我一直在尝试做一个简单的 API 获取，但我不明白我做错了什么我已经阅读了很多问题，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) 给出了想要的结果，所以就好像数据没有被传递一样..我不明白为什么

来自 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"
    }
]

感谢您的帮助

Answer 1

你应该初始化 state.data 像这样尝试。

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

Answer 2

我刚刚解决了几件事：

定义数据的状态

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

迭代前检查你的数组

{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 3

我想我明白问题所在了！！！当您设置新状态时，它会替换之前的状态。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，因此它抛出异常。

与其重新分配整个状态，不如尝试仅替换需要更改的内容：

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

因此，无论何时调用您的 set_state 方法，您都应该添加您的 ...state，这样您就不会遇到这个问题。

TypeError: Cannot read property 'map' of undefined while fetching from API

TypeError: Cannot read property 'map' of undefined while fetching from API

javascript

reactjs

array.prototype.map