使用地图时反应'无法读取未定义的属性'

Question

我正在从teamtreehouse.com制作一个非常基本的React应用程序，并且不断遇到

“ TypeError：无法读取未定义的属性’onPlayerScoreChange’”

即使我正确绑定了我的功能（我认为）

'onPlayerScoreChange'是Grandparent组件中的一种方法，当用户单击“ +”或“-”按钮以更改玩家得分时执行。

如果有人可以解释什么地方出了错，那将非常有帮助，因为我认为我是this.onPlayerScoreChange = this.onPlayerScoreChange.bind(this)在曾祖父母的构造函数中进行设置的。

父组件：

class App extends React.Component {
constructor(props) {
    super(props);
    this.onPlayerScoreChange = this.onPlayerScoreChange.bind(this)
    this.state = {
        initialPlayers: props.initialPlayers,
    };
}

onPlayerScoreChange(delta, index) {
    this.setState((prevState, props) => {
        return {initialPlayers: this.prevState.initialPlayers[index].score += delta}
    })
}

render() {
    return(
        <div className = "scoreboard">
            <Header title = {this.props.title}/>
            <div className = "players">
                {this.state.initialPlayers.map(function(player, index) {
                    return(
                        <Player 
                        name = {player.name} 
                        score = {player.score} 
                        key = {player.id} 
                        index = {index}
                        onScoreChange = {this.onPlayerScoreChange}
                        />
                    )
                })}
            </div>
        </div>
    )
}}

（组件具有默认的标题道具）

子组件：

class Player extends React.Component {
render() {
    return(
        <div className = "player">
            <div className = "player-name">
                {this.props.name}
            </div>
            <div className = "player-score">
                <Counter score = {this.props.score} onChange = {this.props.onScoreChange} index = {this.props.index}/>
            </div>
        </div>
)
}}

孙子部分：

class Counter extends React.Component {
constructor(props) {
    super(props)
    this.handleDecrement = this.handleDecrement.bind(this)
    this.handleIncrement = this.handleIncrement.bind(this)
}

handleDecrement() {
    this.props.onChange(-1, this.props.index)
}

handleIncrement() {
    this.props.onChange(1, this.props.index)
}

render() {
    return(
        <div className = "counter">
            <button className = "counter-action decrement" onClick = {this.handleDecrement}> - </button>
            <div className = "counter-score"> {this.props.score} </div>
            <button className = "counter-action increment" onClick = {this.handleIncrement}> + </button>
        </div>
)}}

谢谢！

Answer 1

您尚未绑定要使用的map函数onScoreChange = {this.onPlayerScoreChange}，

您可以使用绑定或箭头功能进行绑定

需要PS绑定，因为map函数的上下文不同于React Component上下文，因此this该函数内部不会引用React Components
this，因此您无法访问React Component类的该属性。

具有箭头功能：

 {this.state.initialPlayers.map((player, index)=> {
                return(
                    <Player 
                    name = {player.name} 
                    score = {player.score} 
                    key = {player.id} 
                    index = {index}
                    onScoreChange = {this.onPlayerScoreChange}
                    />
                )
            })}

带绑定

   {this.state.initialPlayers.map(function(player, index) {
                return(
                    <Player 
                    name = {player.name} 
                    score = {player.score} 
                    key = {player.id} 
                    index = {index}
                    onScoreChange = {this.onPlayerScoreChange}
                    />
                )
            }.bind(this))}