由于某种原因,我似乎无法理解这个错误;
我已经研究过回调,包括useEffect
中的代码,但是它对我不起作用(或者我做错了)。
这是代码:
import React, { useEffect, useState } from "react";
import "../css/main.css";
import Node from "./node";
const Pathfinder = () => {
const START_NODE_ROW = 10;
const START_NODE_COL = 15;
const FINISH_NODE_ROW = 10;
const FINISH_NODE_COL = 35;
useEffect(() => {
getGrid();
}, []);
const [grid, setGrid] = useState([]);
const getGrid = () => {
setGrid(getInitGrid());
};
const getInitGrid = () => {
const grid = [];
for (let row = 0; row < 20; row++) {
const currentRow = [];
for (let col = 0; col < 50; col++) {
currentRow.push(createNode(col, row));
}
grid.push(currentRow);
}
return grid;
};
const createNode = (col, row) => {
return {
col,
row,
isStart: row === START_NODE_ROW && col === START_NODE_COL,
isFinish: row === FINISH_NODE_ROW && col === FINISH_NODE_COL,
distance: Infinity,
isVisited: false,
isWall: false,
previousNode: null
};
};
return (
<main id="Pathfinder">
{grid.map((row, rowIdx) => {
return (
<div key={rowIdx}>
{row.map((node, nodeIdx) => {
const { row, col, isFinish, isStart } = node;
return (
<Node
key={nodeIdx}
col={col}
isFinish={isFinish}
isStart={isStart}
row={row}
></Node>
);
})}
</div>
);
})}
</main>
);
};
export default Pathfinder;
我基本上是在制作Nodes组件的网格;
我必须使用useEffect
,因为我试图只使用箭头函数和钩子,并且没有类/ react组件,这就是为什么我不能使用类似componentWillMount
的原因。
答案 0 :(得分:4)
您需要将使用的对象传递给您,将getGrid
函数传递给useEffect
挂钩以删除警告消息。
就像下面这样:
useEffect(() => {
getGrid();
}, [getGrid]);
T.J. Crowder的其他建议,将useCallback
用于getGrid
。您可以按照以下步骤进行操作:
const getGrid = useCallback(() => {
setGrid(getInitGrid());
}, [getInitGrid]);
在此处进一步阅读:
您需要对代码中的getInitGrid
进行同样的操作。
我希望这会有所帮助!
答案 1 :(得分:1)
正如TJ所述,最好将功能getInitGrid
和createNode
移到组件之外。您现在所拥有的方式,将在每个渲染器上重新定义功能,这是不必要的,因为它们不直接与组件状态相关联。
此外,useState
钩子可以使用lazy intitial state,这意味着您可以为初始状态参数传递一个函数,并且根本不需要useEffect钩子。
这就是我最后得到的:
import React, { useState } from "react";
import "../css/main.css";
import Node from "./node";
const START_NODE_ROW = 10;
const START_NODE_COL = 15;
const FINISH_NODE_ROW = 10;
const FINISH_NODE_COL = 35;
const createNode = (col, row) => {
return {
col,
row,
isStart: row === START_NODE_ROW && col === START_NODE_COL,
isFinish: row === FINISH_NODE_ROW && col === FINISH_NODE_COL,
distance: Infinity,
isVisited: false,
isWall: false,
previousNode: null
};
};
const getInitGrid = () => {
const grid = [];
for (let row = 0; row < 20; row++) {
const currentRow = [];
for (let col = 0; col < 50; col++) {
currentRow.push(createNode(col, row));
}
grid.push(currentRow);
}
return grid;
};
const Pathfinder = () => {
const [grid, setGrid] = useState(getInitGrid);
return (
<main id="Pathfinder">
{grid.map((row, rowIdx) => {
return (
<div key={rowIdx}>
{row.map((node, nodeIdx) => {
const { row, col, isFinish, isStart } = node;
return (
<Node
key={nodeIdx}
col={col}
isFinish={isFinish}
isStart={isStart}
row={row}
></Node>
);
})}
</div>
);
})}
</main>
);
};
export default Pathfinder;
答案 2 :(得分:0)
Pathfinder
中的大多数内容是静态的,应将其移到其模块之外;这样也可以解决您遇到的useEffect
问题。所有START_NODE_ROW
等const,getInitGrid
和createNode
都是静态的,因此无需每次都重新创建它们。我也将getGrid
包装在useCallback
中,并且可能会稍微重新排列它们,以便仅在定义它们之后才使用它们,但这主要是供人类读者使用的,而不是编译器/ JavaScript引擎:
import React, { useEffect, useState } from "react";
import "../css/main.css";
import Node from "./node";
const START_NODE_ROW = 10;
const START_NODE_COL = 15;
const FINISH_NODE_ROW = 10;
const FINISH_NODE_COL = 35;
const getInitGrid = () => {
const grid = [];
for (let row = 0; row < 20; row++) {
const currentRow = [];
for (let col = 0; col < 50; col++) {
currentRow.push(createNode(col, row));
}
grid.push(currentRow);
}
return grid;
};
const createNode = (col, row) => {
return {
col,
row,
isStart: row === START_NODE_ROW && col === START_NODE_COL,
isFinish: row === FINISH_NODE_ROW && col === FINISH_NODE_COL,
distance: Infinity,
isVisited: false,
isWall: false,
previousNode: null
};
};
const Pathfinder = () => {
const [grid, setGrid] = useState([]);
const getGrid = useCallback(() => {
setGrid(getInitGrid());
}, []);
useEffect(() => {
getGrid();
}, []);
return (
<main id="Pathfinder">
{grid.map((row, rowIdx) => {
return (
<div key={rowIdx}>
{row.map((node, nodeIdx) => {
const { row, col, isFinish, isStart } = node;
return (
<Node
key={nodeIdx}
col={col}
isFinish={isFinish}
isStart={isStart}
row={row}
></Node>
);
})}
</div>
);
})}
</main>
);
};
export default Pathfinder;
getGrid
很小,仅使用一次。对我来说,将其分解为自己的功能是不值得的:
import React, { useEffect, useState } from "react";
import "../css/main.css";
import Node from "./node";
const START_NODE_ROW = 10;
const START_NODE_COL = 15;
const FINISH_NODE_ROW = 10;
const FINISH_NODE_COL = 35;
const getInitGrid = () => {
const grid = [];
for (let row = 0; row < 20; row++) {
const currentRow = [];
for (let col = 0; col < 50; col++) {
currentRow.push(createNode(col, row));
}
grid.push(currentRow);
}
return grid;
};
const createNode = (col, row) => {
return {
col,
row,
isStart: row === START_NODE_ROW && col === START_NODE_COL,
isFinish: row === FINISH_NODE_ROW && col === FINISH_NODE_COL,
distance: Infinity,
isVisited: false,
isWall: false,
previousNode: null
};
};
const Pathfinder = () => {
const [grid, setGrid] = useState([]);
useEffect(() => {
setGrid(getInitGrid());
}, []);
return (
<main id="Pathfinder">
{grid.map((row, rowIdx) => {
return (
<div key={rowIdx}>
{row.map((node, nodeIdx) => {
const { row, col, isFinish, isStart } = node;
return (
<Node
key={nodeIdx}
col={col}
isFinish={isFinish}
isStart={isStart}
row={row}
></Node>
);
})}
</div>
);
})}
</main>
);
};
export default Pathfinder;
(您不必将setGrid
或getInitGrid
声明为依赖项,因为第一个是React的状态设置器函数guaranteed to be stable,第二个是在{之外定义的{1}}。)