TypeError：TypeError：未定义不是对象（正在评估“ _this.state.scheduleList”）

Question

export default class ScheduleDayTest extends React.Component {
constructor(props) {
    super(props);

    this.state = {
        scheduleList: [
            {
                id: 1,
                title: 'Arrival & Registration',
                type: 'Organizational',
                time: '3:00 PM',
                location: 'Main Lobby',
                message: 'Arrival at this time',
            },
            {
                id: 2,
                title: 'English Program Opening Statement',
                type: 'English Program',
                time: '6:00 PM - 6:30 PM',
                location: 'Lilac AC',
                message: 'Welcome to the 32nd annual conference',
            },
            {
                id: 3, 
                title: 'Arabic Program Opening Statement',
                type: 'Arabic Program',
                time: '6:00 PM - 6:30 PM',
                location: 'Lilac BD',
                message: 'Welcome to the 32nd annual conference',
            },
            {
                id: 4,
                title: 'Opening Ceremony',
                type: 'Organizational',
                time: '8:00 PM - 10:00 PM',
                location: 'Harry Ballroom',
                message: 'Opening Ceremony',
            },
          ],
        index: this.getIndex(this.props.navigation.state.params.itemID),
    }

}

getIndex = (itemID) => {
    for(let i = 0; i < this.state.scheduleList.length; i++) {
        if (this.state.scheduleList[i].id === itemID) {
            console.log(i);
            return i;
        }
    }
    return 0;
}

我试图调用getIndex函数来初始化索引状态变量，但是我不断收到这样的错误消息：即使声明了它，“ this.state.scheduleList”也不存在。任何帮助都会很棒。

Answer 1

您在初始化状态时正在调用getIndex，因此它将是未定义的。 请尝试以下

export default class ScheduleDayTest extends React.Component {
    constructor(props) {
        super(props);

        const scheduleList = [
            {
                id: 1,
                title: 'Arrival & Registration',
                type: 'Organizational',
                time: '3:00 PM',
                location: 'Main Lobby',
                message: 'Arrival at this time',
            },
            {
                id: 2,
                title: 'English Program Opening Statement',
                type: 'English Program',
                time: '6:00 PM - 6:30 PM',
                location: 'Lilac AC',
                message: 'Welcome to the 32nd annual conference',
            },
            ...
        ];
        this.state = {
            scheduleList,
            index: scheduleList.findIndex(item => item.id === this.props.navigation.state.params.itemID),
        }

    }   
}