React教程：TicTacToe，使用map（）

Question

我正在尝试使用.map()方法在React教程的TicTacToe示例中呈现一行。

我希望看到四行三框。但是我只看到三行。 Here is the Codepen.

https://codepen.io/anon/pen/WKygVM?editors=0011

render() {
  const status = 'Next player: X';
  const rc = [0, 1, 2];
  const rowItems = rc.map((n) => {
    console.log(n);
    this.renderSquare(n);
  });

  return (
    <div>
      <div className="status">{status}</div>
      // I expect the below row to render the first row,
      // on top of the three that are manually rendered
      <div className="board-row">{this.rowItems}</div>

编辑：Codepen is now solved.

Answer 1

两个问题：

• map需要返回每个返回的值。

const rowItems = rc.map((n) => {
    console.log(n);
    return this.renderSquare(n);
});
// const rowItems = rc.map((n) => this.renderSquare(n)); /* with arrow functions */

• 它只是rowItems，而不是this.rowItems，因为它只是上面定义的变量（不是在实际类中定义的方法）

<div className="board-row">{rowItems}</div>

---

请注意，这将返回警告：

  

Warning: Each child in an array or iterator should have a unique "key" prop.

只希望您向正在循环的节点添加一个key属性。

renderSquare(i) {
    return <Square key={i} value={i} />;
}

class Square extends React.Component {
  render() {
    return (
      <button className="square"
        onClick={() => { 
          // console.log('click');
          console.log('value', this.props.value);
        }}>
        {this.props.value}
      </button>
    );
  }
}

class Board extends React.Component {
  renderSquare(i) {
    return <Square key={i} value={i} />;
  }

  render() {
    const status = 'Next player: X';
    const rc = [0, 1, 2];
    const rowItems = rc.map((n) => {
      console.log(n);
      return this.renderSquare(n);
    });

    return (
      <div>
        <div className="status">{status}</div>
        <div className="board-row">{rowItems}</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 {
  render() {
    return (
      <div className="game">
        <div className="game-board">
          <Board />
        </div>
        <div className="game-info">
          <div>{/* status */}</div>
          <ol>{/* TODO */}</ol>
        </div>
      </div>
    );
  }
}

// ========================================

ReactDOM.render(
  <Game />,
  document.getElementById('root')
);

body {
  font: 14px "Century Gothic", Futura, sans-serif;
  margin: 20px;
}

ol, ul {
  padding-left: 30px;
}

.board-row:after {
  clear: both;
  content: "";
  display: table;
}

.status {
  margin-bottom: 10px;
}

.square {
  background: #fff;
  border: 1px solid #999;
  float: left;
  font-size: 24px;
  font-weight: bold;
  line-height: 34px;
  height: 34px;
  margin-right: -1px;
  margin-top: -1px;
  padding: 0;
  text-align: center;
  width: 34px;
}

.square:focus {
  outline: none;
}

.kbd-navigation .square:focus {
  background: #ddd;
}

.game {
  display: flex;
  flex-direction: row;
}

.game-info {
  margin-left: 20px;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>
<div id="errors" style="
  background: #c00;
  color: #fff;
  display: none;
  margin: -20px -20px 20px;
  padding: 20px;
  white-space: pre-wrap;
"></div>
<div id="root"></div>
<script>
window.addEventListener('mousedown', function(e) {
  document.body.classList.add('mouse-navigation');
  document.body.classList.remove('kbd-navigation');
});
window.addEventListener('keydown', function(e) {
  if (e.keyCode === 9) {
    document.body.classList.add('kbd-navigation');
    document.body.classList.remove('mouse-navigation');
  }
});
window.addEventListener('click', function(e) {
  if (e.target.tagName === 'A' && e.target.getAttribute('href') === '#') {
    e.preventDefault();
  }
});
window.onerror = function(message, source, line, col, error) {
  var text = error ? error.stack || error : message + ' (at ' + source + ':' + line + ':' + col + ')';
  errors.textContent += text + '\n';
  errors.style.display = '';
};
console.error = (function(old) {
  return function error() {
    errors.textContent += Array.prototype.slice.call(arguments).join(' ') + '\n';
    errors.style.display = '';
    old.apply(this, arguments);
  }
})(console.error);
</script>