为什么调用此变量会错过它所包含的数组？

Question

在React的在线教程中，您将指导您使用以下代码创建一个井字游戏:

import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';
function Square(props) {
return (
<button className="square" onClick={props.onClick}>
{props.value}
</button>
);
}
class Board extends React.Component {
renderSquare(i) {
return (
<Square 
value={this.props.squares[i]}
onClick={() => this.props.onClick(i)}
/>
);
}
render() {
return (
<div>
<div className="board-row">
{this.renderSquare(0)}
{this.renderSquare(1)}
{this.renderSquare(2)}
</div>
<div className="board-row">
{this.renderSquare(3)}
{this.renderSquare(4)}
{this.renderSquare(5)}
</div>
<div className="board-row">
{this.renderSquare(6)}
{this.renderSquare(7)}
{this.renderSquare(8)}
</div>
</div>
);
}
}
class Game extends React.Component {
constructor(props) {
super(props);
this.state = {
history: [{
squares: Array(9).fill(null),
}],
stepNumber:0,
xIsNext: true,
};
}
handleClick(i) {
const history = this.state.history.slice(0, this.state.stepNumber + 1);
const current = history[history.length - 1];
const squares = current.squares.slice();
if(calculateWinner(squares) || squares[i]) {
return;
}
squares[i] = this.state.xIsNext ? 'X' : 'O';
this.setState({
history: history.concat([{
squares:squares,
}]),
stepNumber: history.length,
xIsNext: !this.state.xIsNext,
}); 
}
jumpTo(step) {
this.setState({
stepNumber: step,
xIsNext: (step % 2) === 0,
});
}
render() {
const history = this.state.history;
const current = history[this.state.stepNumber];
const winner = calculateWinner(current.squares);
const moves = history.map((step, move) => {
const desc = move ?
'Go to move #' + move :
'Go to game start';
return(
<li key={move}>
<button onClick={() => this.jumpTo(move)}>{desc}</button>
</li>
);
});
let status;
if(winner){
status = 'Winner: ' + winner;
} else{
if(this.state.stepNumber === 9){
status = 'Draw!';
} else{
status = 'Next player: ' + (this.state.xIsNext ? 'X' : 'O');
}
}
return (
<div className="game">
<div className="game-board">
<Board 
squares={current.squares}
onClick={(i) => this.handleClick(i)}
/>
</div>
<div className="game-info">
<div>{status}</div>
<ol>{moves}</ol>
</div>
</div>
);
}
}
function calculateWinner(squares) {
const lines = [
[0, 1, 2],
[3, 4, 5],
[6, 7, 8],
[0, 3, 6],
[1, 4, 7],
[2, 5, 8],
[0, 4, 8],
[2, 4, 6],
];
for (let i = 0; i < lines.length; i++) {
const [a, b, c] = lines[i];
if (squares[a] && squares[a] === squares[b] && squares[a] === squares[c]) {
return squares[a];
}
}
return null;
}
// ========================================
ReactDOM.render(
<Game />,
document.getElementById('root')

我的问题很简单。在Board类中，当调用this.props.squares[i]时。为什么我们忽略了正方形所在的历史数组?这个调用不应该是this.props.history.squares[i]吗?

Answer 1

让我们将其分解为一些变量的声明:

const history = [{ squares: Array(9).fill(null) }]
// history = [{ squares: [null, null, null, ...] }]
const current = history[0]
// current = { squares: [null, null, null, ...] }

现在你通过Board:

<Board
squares = {current.squares}
// squares = [null, null, null, ...]

实际上，你只是将Array传递给你的道具并且可以通过this.props.squares[i]

访问它如果你想使用this.props.history.squares[i]，首先你应该使用this.props.history[step].squares[i](history和squares都是数组)，其次-你应该传递

// Game
<Board 
squares = {history}
...