【发布时间】：2017-03-08 11:42:44
【问题描述】：
我是 Angular（以及 Javascript）的新手。我编写了一个返回用户数组的 Angular 服务。从 HTTP 调用中检索数据，该调用以 JSON 格式返回数据。当记录从 HTTP 调用返回的 JSON 数据时，我可以看到这个调用成功并且返回了正确的数据。我有一个调用服务来获取用户的组件和一个显示用户的 HTML 页面。我无法从服务获取数据到组件。我怀疑我错误地使用了 Observable。也许我也错误地使用了订阅。如果我注释掉 ngInit 函数中的 getUsers 调用并取消注释 getUsersMock 调用，一切正常，我会看到 HTML 页面的列表框中显示的数据。我想将 JSON 数据转换为服务中的用户数组或列表，而不是从服务返回 JSON 并让组件对其进行转换。
从 HTTP 调用返回的数据以获取用户：
[
{
"firstName": "Jane",
"lastName": "Doe"
},
{
"firstName": "John",
"lastName": "Doe"
}
]
user.ts
export class User {
firstName: string;
lastName: string;
}
用户服务.ts
...
@Injectable
export class UserService {
private USERS: User[] = [
{
firstName: 'Jane',
lastName: 'Doe'
},
{
firstName: 'John',
lastName: 'Doe'
}
];
constructor (private http: Http) {}
getUsersMock(): User[] {
return this.USERS;
}
getUsers(): Observable<User[]> {
return Observable.create(observer => {
this.http.get('http://users.org').map(response => response.json();
})
}
...
user.component.ts
...
export class UserComponent implements OnInit {
users: User[] = {};
constructor(private userService: UserService) {}
ngOnInit(): void {
this.getUsers();
//this.getUsersMock();
}
getUsers(): void {
var userObservable = this.userService.getUsers();
this.userObservable.subscribe(users => { this.users = users });
}
getUsersMock(): void {
this.users = this.userService.getUsersMock();
}
}
...
user.component.html
...
<select disabled="disabled" name="Users" size="20">
<option *ngFor="let user of users">
{{user.firstName}}, {{user.lastName}}
</option>
</select>
...
！！！更新！！！
我一直在阅读“英雄”教程，但不适合我，所以我开始尝试其他方法。我已经按照英雄教程描述的方式重新实现了我的代码。但是，当我记录 this.users 的值时，它会报告 undefined。
这是我修改后的 user-service.ts
...
@Injectable
export class UserService {
private USERS: User[] = [
{
firstName: 'Jane',
lastName: 'Doe'
},
{
firstName: 'John',
lastName: 'Doe'
}
];
constructor (private http: Http) {}
getUsersMock(): User[] {
return this.USERS;
}
getUsers(): Promise<User[]> {
return this.http.get('http://users.org')
.toPromise()
.then(response => response.json().data as User[])
.catch(this.handleError);
}
...
这是我修改后的 user.component.ts
...
export class UserComponent implements OnInit {
users: User[] = {};
constructor(private userService: UserService) {}
ngOnInit(): void {
this.getUsers();
//this.getUsersMock();
}
getUsers(): void {
this.userService.getUsers()
.then(users => this.users = users);
console.log('this.users=' + this.users); // logs undefined
}
getUsersMock(): void {
this.users = this.userService.getUsersMock();
}
}
...
!!!!!!!!!!最终工作解决方案!!!!!!!!!! 这是最终工作解决方案的所有文件：
user.ts
export class User {
public firstName: string;
}
user.service.ts
import { Injectable } from '@angular/core';
import { Http, Response } from '@angular/http';
import { Observable } from 'rxjs/Observable';
import 'rxjs/add/operator/catch';
import 'rxjs/add/operator/map';
import { User } from './user';
@Injectable()
export class UserService {
// Returns this JSON data:
// [{"firstName":"Jane"},{"firstName":"John"}]
private URL = 'http://users.org';
constructor (private http: Http) {}
getUsers(): Observable<User[]> {
return this.http.get(this.URL)
.map((response:Response) => response.json())
.catch((error:any) => Observable.throw(error.json().error || 'Server error'));
}
}
user.component.ts
import { Component, OnInit } from '@angular/core';
import { Router } from '@angular/router';
import { User } from './user';
import { UserService } from './user.service';
@Component({
moduleId: module.id,
selector: 'users-list',
template: `
<select size="5">
<option *ngFor="let user of users">{{user.firstName}}</option>
</select>
`
})
export class UserComponent implements OnInit{
users: User[];
title = 'List Users';
constructor(private userService: UserService) {}
getUsers(): void {
this.userService.getUsers()
.subscribe(
users => {
this.users = users;
console.log('this.users=' + this.users);
console.log('this.users.length=' + this.users.length);
console.log('this.users[0].firstName=' + this.users[0].firstName);
}, //Bind to view
err => {
// Log errors if any
console.log(err);
})
}
ngOnInit(): void {
this.getUsers();
}
}
【问题讨论】：
标签： arrays json angular rxjs angular2-http