为什么 useState 值没有在 useHotkeys 回调中更新？

Question

我有以下搜索建议 React hooks 使用react-hotkeys-hooks来管理按键。

为什么selectedUserItem不在按键Enter上更新？ 当向上和向下键改变时它保持为 0。

import { useHotkeys } from "react-hotkeys-hook";
import React, { useState } from "react";

import "./styles.css";
const itemsByName = [
  {
    id: 1,
    name: "Ice Cream"
  },
  {
    id: 2,
    name: "Banana Pudding"
  },
  {
    id: 3,
    name: "Chocolate Cake"
  },
  {
    id: 4,
    name: "Sponge Cake"
  },
  {
    id: 5,
    name: "Carrot Cake"
  }
];

const App = () => {
  const [selectedUserItem, setSelectedUserItem] = useState(0);

  // const [create] = useMutation(SAVE_USER_ITEM, {
  //   refetchQueries: ["UserItemsQuery"]
  // })

  const itemSelect = (e, item) => {
    e.preventDefault();
    // create({ variables: { input: { id: item.id } } });
    // console.log(item)
  };

  const increment = selectedUserItem => {
    const max = itemsByName.length - 1;
    return max > selectedUserItem ? selectedUserItem + 1 : max;
  };

  const decrement = selectedUserItem => {
    const min = 0;
    return min < selectedUserItem ? selectedUserItem - 1 : min;
  };

  useHotkeys(
    "*",
    (event, handler) => {
      // console.log(handler)
      switch (event.key) {
        case "ArrowDown":
          setSelectedUserItem(selectedUserItem => increment(selectedUserItem));
          break;
        case "ArrowUp":
          setSelectedUserItem(selectedUserItem => decrement(selectedUserItem));
          break;
        case "Enter":
          console.log(selectedUserItem);
          const userItem = itemsByName[selectedUserItem];
          console.log(userItem);
          break;
        default:
          console.log(event.key);
          break;
      }
    },
    {
      filter: () => true
    }
  );

  return (
    <div className="absolute w-3/4 mt-16 ml-8 py-2 bg-white shadow-xl rounded-lg">
      <h1>Index: {selectedUserItem}</h1>
      {itemsByName.map((item, i) => {
        return (
          <div
            href="#"
            onClick={e => itemSelect(e, item)}
            className={`${selectedUserItem === i ? "hovered" : ""} dessert`}
            key={item.id}
          >
            {item.id}: {item.name}
          </div>
        );
      })}
    </div>
  );
};

export default App;

Answer 1

useHotkeys内部使用useCallback和useEffect钩子，这需要知道它的某些依赖项何时发生变化。 为了确保它与这些钩子一起工作良好，useHotkeys提供传递一个deps array ，就像提到的其他钩子一样，作为它的最后一个参数。

deps: any[] = [] ：附加到回调记忆的依赖数组。 在这里您定义回调的内部依赖关系。 例如，如果您的回调操作依赖于一个引用不稳定的值或一个会随时间变化的值，您应该将此值添加到您的deps数组中。 由于大多数时候你的回调不会依赖于任何不稳定的回调或随时间变化的值，你可以不理会这个值，因为它默认设置为空数组。

在您的代码中，它看起来像这样：

// These never changes and do not rely on the component scope, so they
// can be defined safely outside the component.
const increment = selectedUserItem => {
  const max = itemsByName.length - 1;
  return max > selectedUserItem ? selectedUserItem + 1 : max;
};

const decrement = selectedUserItem => {
  const min = 0;
  return min < selectedUserItem ? selectedUserItem - 1 : min;
};

const App = () => {
  const [selectedUserItem, setSelectedUserItem] = useState(0);

  useHotkeys(
    "*",
    (event, handler) => {
      switch (event.key) {
        case "ArrowDown":
          setSelectedUserItem(increment);
          break;
        case "ArrowUp":
          setSelectedUserItem(decrement);
          break;
        case "Enter":
          console.log(selectedUserItem, itemsByName[selectedUserItem]);
          break;
        default:
          console.log(event.key);
          break;
      }
    },
    {
      filter: () => true
    },
    // The dependencies array which ensure that the data is up to date in the callback.
    [selectedUserItem, setSelectedUserItem]
  );

  // rest of the component