从Angular服务获取对象数组

Question

我是Angular的新手（和Javascript一样）。我写了一个Angular服务，它返回一个用户数组。从HTTP调用中检索数据，该调用以JSON格式返回数据。记录从HTTP调用返回的JSON数据时，我可以看到此调用成功并返回正确的数据。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。我怀疑我正在使用Observable。也许我正在使用订阅错误。如果我在ngInit函数中注释掉getUsers调用并取消注释getUsersMock调用，那么一切正常，我看到HTML页面中列表框中显示的数据。我想将JSON数据转换为服务中的数组或用户列表，而不是从服务返回JSON并让组件转换它。

从HTTP调用返回的数据获取用户：

[
    {
        "firstName": "Jane",
        "lastName": "Doe"
    },
    {
        "firstName": "John",
        "lastName": "Doe"
    }
]

user.ts

export class User {
    firstName: string;
    lastName: string;
}

用户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(): 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，但没有为我工作，所以我去了尝试其他的东西。我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。

这是我修改过的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);
    }
...

这是我修改过的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();
    }
}
...

!!!!!!!!!!最终的工作解决方案!!!!!!!!!!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();
    }
}

Answer 1

看看你的代码：

 getUsers(): Observable<User[]> {
        return Observable.create(observer => {
            this.http.get('http://users.org').map(response => response.json();
        })
    }

和来自https://angular.io/docs/ts/latest/tutorial/toh-pt6.html的代码（BTW。非常好的教程，你应该看一下）

 getHeroes(): Promise<Hero[]> {
    return this.http.get(this.heroesUrl)
               .toPromise()
               .then(response => response.json().data as Hero[])
               .catch(this.handleError);
  }

Angular2中的HttpService已经返回一个observable，你不需要像你在这里那样包装另一个Observable：

   return Observable.create(observer => {
        this.http.get('http://users.org').map(response => response.json()

尝试按照我提供的链接中的指南。当你仔细研究它时，你应该没问题。

- -编辑 - -

首先，你在哪里记录this.users变量？ JavaScript不是这样工作的。你的变量是未定义的，这很好，因为代码执行顺序！

尝试这样做：

  getUsers(): void {
        this.userService.getUsers()
            .then(users => {
               this.users = users
               console.log('this.users=' + this.users);
            });


    }

查看console.log（...）的位置！

尝试从toPromise（）辞职似乎只适用于没有RxJs背景的人。

抓住另一个链接：https://scotch.io/tutorials/angular-2-http-requests-with-observables使用RxJs observables再次构建您的服务。