reactjs - TypeError:无法在渲染视图中读取 null 的属性“投票”
问题描述
在这个组件中,我在属性中获得了一个 Promise 对象,我尝试将其置于状态,但是当视图被渲染时,我收到消息“TypeError:无法读取属性'vote' of null”,要求解决我的问题问题,我花了两个小时,我没有看到结束。我应该怎么做?
import { IVoteDetailsProps } from "./IVoteDetailsProps";
import { IVoteDetailsState } from "./IVoteDetailsState";
export class VoteDetails extends React.Component<IVoteDetailsProps, IVoteDetailsState>{
constructor(props: IVoteDetailsProps) {
super();
console.log(props)
}
componentDidMount() {
let data = this.props.voteDetails;
data.then(result => this.setState({
vote: result
}));
};
public render(): React.ReactElement<IVoteDetailsState> {
return (
<table >
<tbody>
{this.state.vote && this.state.vote.map(el => {
<tr id={el.id.toString()}>
<td>{el.title}</td>
<td>{el.voteType}</td>
</tr>
})}
</tbody>
</table>
)
}
}
export interface IVoteDetailsProps {
voteDetails: Promise<IVoteDetailsData[]>;
}
export interface IVoteDetailsData{
id: number;
title: string;
voteType: string;
}
import React = require("react");
import { VoteDetails } from "../VoteDetails/VoteDetails";
import { IVoteListProps } from "./IVoteListProps";
export class VoteList extends React.Component<IVoteListProps, {}> {
constructor(props: IVoteListProps) {
super(props);
console.log(props)
}
public render(): React.ReactElement<IVoteListProps> {
// const { vote } = this.state;
return (
<VoteDetails voteDetails={this.props.adminServicePanel.getVotesInfo()} />
)
};
}
public render(): React.ReactElement<IVoteSecurityAppProps> {
return (
<main className="ui main text container">
<VoteList adminServicePanel={this.props.adminPanelService}/>
</main>
);
import {HttpClient} from '@microsoft/sp-http';
import { reject } from 'lodash';
import {IAdminPanelService} from './IAdminPanelService';
import {IReportData} from './IReportData'
import { IVoteDetailsData } from './IVoteDetailsData';
import {IVoteInfo} from './IVoteInfo'
import {VoteOptions} from './VoteOptions';
export class AdminPanelService implements IAdminPanelService {
//////////////////////////////MOCK////////////////////////////////////////////
private voteInfos : IVoteDetailsData[];
private reportData : IReportData[];
//////////////////////////////MOCK////////////////////////////////////////////
constructor(private httpClient: HttpClient, private serverRelativeSiteUrl: string) {
//MOCK
this.voteInfos = [
{
id : 1,
title : "xxx",
voteType : "xx"
},
{
id : 2,
title : "xxx",
voteType : "xxx"
}
];
}
public getVotesInfo () : Promise<IVoteDetailsData[]> {
return new Promise<IVoteDetailsData[]>((resolve : (voteMiniInfo : IVoteDetailsData[]) => void, reject : (error: any) => void): void =>{
resolve(this.voteInfos);
})
}
}
export interface IAdminPanelService {
getVotesInfo:() => Promise<IVoteDetailsData[]>;
}
解决方案
当您调用时,spfx 组件中的所有错误“TypeError: Cannot read property '......' of null”
this.state.{varname}
或者
this.props.{varname}
解决以下问题之一:
- 在构造函数中将绑定“this”添加到出现错误的方法
this.{methodname} = this.{methodname}.bind(this)
- 您错过了构造函数中的初始化状态(对于 React.Component<props,state>)
this.state = {};
- 您使用道具或状态中的值并错过检查它是否为空
在问题中,我看到了所有这些事情。例如,在这段代码中,状态不会被初始化,否则组件有状态
export class VoteDetails extends React.Component<IVoteDetailsProps, IVoteDetailsState>{
constructor(props: IVoteListProps) {
super(props);
console.log(props)
//this.state == null - true
}
}
第二个问题是这段代码
<VoteDetails voteDetails={this.props.adminServicePanel.getVotesInfo()}
getVotesInfo- 返回承诺,而不是数据。这种不好的做法,例如使用状态来保存数据
constructor(props: ...){
super(props);
this.state{
data: null
};
this._getData = this._getData.bind(this);
}
componentDidMount(){
this._getData();
}
async _getData(){
if(this.props.adminServicePanel){
let data = await this.props.adminServicePanel.getVotesInfo();
this.setStae({data});
}
}
render():...{
const data = this.state.data;
return(
{data && data.map(...)}
);
}