ERROR TypeError: Cannot read property '_id' of undefined at Object.eval [as updateDirectives]

Question

我在数据绑定 _id 属性后收到此错误。谁能帮帮我。

代码：

<div class="form-group">
  <input type="hidden" name="_id" #_id="ngModel" [(ngModel)]="iphoneService.selectedIphone._id">
</div>

这是iphone.Service代码

import { Injectable } from "@angular/core";
import { HttpClient } from "@angular/common/http";
import { Observable } from "rxjs/Observable";
import "rxjs/add/operator/map";
import "rxjs/add/operator/toPromise";

import { Iphone } from "./iphone.model";

@Injectable()
export class IphoneService {
  selectedIphone: Iphone;
  iphones: Iphone[];
  readonly baseUrl = "http://localhost:3000/iphone";

  constructor(private http: HttpClient) {}

  postIphone(iphon: Iphone) {
    return this.http.post(this.baseUrl, iphon);
  }
}

这是iphon.model

export interface Iphone {
_id: string;
firstName: string;
lastName: string;
email: string;
colorPrefence: string;
contact: string;
country: string;
state: string;
city: string;
zipCode: string;
transactionId: string;
__v: string;

}

这里是iphone.component.ts

@Component({
selector: "app-iphone",
templateUrl: "./iphone.component.html",
styleUrls: ["./iphone.component.css"],
providers: [IphoneService]
})
export class IphoneComponent implements OnInit, AfterViewChecked {
constructor(public iphoneService: IphoneService) {}

ngOnInit() {}

onSubmit(form: NgForm) {
this.iphoneService.postIphone(form.value).subscribe(res => {});

}

我认为我遇到的错误是由于模型绑定不正确，但我不知道如何解决它。

Answer 1

您在制定工作流程时遇到了几个问题。

首先，您尝试绑定到存在于服务中而非组件中的变量。服务不应该负责存储视图状态。视图状态应该是组件的责任。您需要在您的组件上有一个变量（例如 selectedIphoneId），然后您可以在 [(ngModel)] 中使用它。

同时删除模板引用的分配 #_id=“ngModel。如果您甚至不需要使用它，请摆脱它。你会得到这样的东西：

<div class="form-group">
    <input type="hidden" name="_id" #_id [(ngModel)]="selectedIphoneId">
  </div>

ERROR TypeError: Cannot read property '_id' of undefined at Object.eval [as updateDirectives]

ERROR TypeError: Cannot read property '_id' of undefined at Object.eval [as updateDirectives]

angular

angular-ngmodel