[英]Angular2 Http Undefined error
我正在嘗試使用Angular2(角度2.0.0-beta.0和打字稿1.7.5)中的Http模塊發出get請求,但是我遇到了某種同步問題。 我將所有內容都放在一個.ts文件中,以使其更易於通信。
在打字稿中一切都可以正常編譯,但是Chrome在控制台中顯示以下錯誤:
EXCEPTION: TypeError: Cannot read property '_id' of undefined in [Id: {{contact._id}} Name: {{contact.name}} in Test@1:13]
ORIGINAL EXCEPTION: TypeError: Cannot read property '_id' of undefined
ORIGINAL STACKTRACE:
TypeError: Cannot read property '_id' of undefined
...
...
Object {_id: "5695e53d98ff94671ae22d55", name: "Piet Pannenkoek", email: "piet@gmail.com", number: "435345"}
test1.ts:
import {bootstrap} from 'angular2/platform/browser';
import {Component} from 'angular2/core';
import {Http, Response, HTTP_PROVIDERS} from 'angular2/http';
import 'rxjs/Rx';
@Component({
selector: 'my-app',
template: `
<div>Id: {{contact._id}} Name: {{contact.name}}</div>
`,
providers: [HTTP_PROVIDERS]
})
export class Test {
public contact: Contact;
constructor(private http: Http) {}
ngAfterViewInit() {
this.http.get('/api/contactlist/5695e53d98ff94671ae22d55')
.map((res: Response) => res.json())
.subscribe(res => {
console.log(res);
this.contact = res;
});
}
}
export class Contact {
constructor (public _id: string, public name: string, public email: string, public number: string) {};
}
bootstrap(Test);
HTTP://本地主機:3000 / API / contactlist / 5695e53d98ff94671ae22d55
{"_id":"5695e53d98ff94671ae22d55","name":"Piet Pannenkoek","email":"piet@gmail.com","number":"435345"}
奇怪的是另一個(略有不同)版本test2.ts沒有給出任何錯誤:
import {bootstrap} from 'angular2/platform/browser';
import {Component} from 'angular2/core';
import {Http, Response, HTTP_PROVIDERS} from 'angular2/http';
import 'rxjs/Rx';
@Component({
selector: 'my-app',
template: '<div *ngFor="#contact of contacts">Id: {{contact._id}} Name: {{contact.name}}</div>',
providers: [HTTP_PROVIDERS]
})
export class Test {
public contacts: Contact[] = [];
constructor(private http: Http) {}
ngAfterViewInit() {
this.http.get('/api/contactlist')
.map((res: Response) => res.json())
.subscribe(res => {
console.log(res);
this.contacts = res;
});
}
}
export class Contact {
constructor (public _id: string, public name: string, public email: string, public number: string) {};
}
bootstrap(Test);
HTTP://本地主機:3000 / API / contactlist
[{"_id":"5695e53d98ff94671ae22d55","name":"Piet Pannenkoek","email":"piet@gmail.com","number":"435345"},{"_id":"56a63059b2cb5f4b10efaf9a","name":"Jan Janssen","email":"jan@email.com","number":"642"},{"_id":"56a6307bb2cb5f4b10efaf9b","name":"Gerard de Boer","email":"gerard@email.com","number":"1234"},{"_id":"56abe853211b52a441f6c45f","name":"Bjorn Borg","email":"bjorn@borg.com","number":"123"},{"_id":"56abe8da211b52a441f6c460","name":"Hans Dobbelsteen","email":"hans@email.com","number":"752"},{"_id":"56abe8fe211b52a441f6c461","name":"Marco van Basten","email":"marco@email.com","number":"961"}]
您正在嘗試使用contact
對象,但無法解決。 使用elvis-operator {{ contact?._id }}
或有條件地顯示塊:
template: `
<div *ngIf="contact">Id: {{contact._id}} Name: {{contact.name}}</div>
`,
您正在嘗試訪問contact
對象,直到模板加載之前,該對象是未定義/為空,即在模板加載時您的對象尚未正確加載。 因此,為了避免這種情況,您必須使用如下所示的elvis
運算符
{{contact?._id}} and {{contact?.name}}
如果您的contact
對象沒有名為name
或id
值,則使用elvis
運算符angualr不會引發任何錯誤。 只要您的綁定加載正確以contact
對象角度,就會反射對模板的更改。
試試這個肯定為您工作。
<div>Id: {{contact?._id}} Name: {{contact?.name}}</div>
Angular嘗試在數據到達之前進行綁定。
<div>Id: {{contact?._id}} Name: {{contact?.name}}</div>
應該管用。
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