Angular 2-无法读取未定义的属性"get"(http未定义) [英] Angular 2 - Cannot read property 'get' of undefined (http undefined)

问题描述

Angular2的新手，遇到了奇怪的问题.呈现index.html时，app.component呈现html部分，但在 user.service.ts 中的数据调用上失败-特别是http未定义(下面的代码).

Novice to Angular2 and running into strange issue. When rendering index.html the app.component renders the html part OK, but it fails on data call in user.service.ts - specifically http is undefined (code below).

浏览器错误

app.module.ts

import { NgModule } from '@angular/core';
import { HttpModule } from '@angular/http';
import { BrowserModule } from '@angular/platform-browser';
import { AppComponent }   from './app.component';
@NgModule({
    imports: [
        BrowserModule,
        HttpModule],
  declarations: [ AppComponent ],
  bootstrap:    [ AppComponent ]
})
export class AppModule { }

main.ts

import { platformBrowserDynamic } from '@angular/platform-browser-dynamic';
import { AppModule } from './app.module';
const platform = platformBrowserDynamic();
platform.bootstrapModule(AppModule); 

user.service

import { Component, Injectable } from '@angular/core';
import { Http, Headers, Response } from '@angular/http';
import { Observable } from 'rxjs/Observable';
import 'rxjs/add/operator/map';
import { User } from '../models/user';

@Injectable()
export class UserService {
    private user: User;

    constructor(private http: Http) {

    }

    getCurrentUser() {
        return this.http.get('http://jsonplaceholder.typicode.com/posts')
            .map((request: any) => {
                return this.user = {
                    id: 'testID',
                    firstName: 'fname test',
                    lastName: 'lastname Test',
                    displayName: 'display name test'
                }

            });
    }
}

app.component.ts

import { Component, OnInit, Inject } from '@angular/core';
import { UserService } from './services/user.service';
import { User } from './models/user';

@Component({
    selector: 'my-app',
    templateUrl: 'app/app.component.html',
    providers: [UserService]
})
export class AppComponent implements OnInit {
    user: User;

    constructor(
        @Inject(UserService) private _userService: UserService) {
    }
    getCurrentUser() {
        this._userService.getCurrentUser()
            .subscribe(user => this.user = user);
    }
    ngOnInit() {
        this.getCurrentUser();
    }
}

system.config

map: {
        // our app is within the app folder
        app: 'public/dist/js',
        // angular bundles
        '@angular/core': 'node_modules/@angular/core/bundles/core.umd.js',
        '@angular/common': 'node_modules/@angular/common/bundles/common.umd.js',
        '@angular/compiler': 'node_modules/@angular/compiler/bundles/compiler.umd.js',
        '@angular/platform-browser': 'node_modules/@angular/platform-browser/bundles/platform-browser.umd.js',
        '@angular/platform-browser-dynamic': 'node_modules/@angular/platform-browser-dynamic/bundles/platform-browser-dynamic.umd.js',
        '@angular/http': 'node_modules/@angular/http/bundles/http.umd.js',
        '@angular/router': 'node_modules/@angular/router/bundles/router.umd.js',
        '@angular/forms': 'node_modules/@angular/forms/bundles/forms.umd.js',
        // other libraries
        'rxjs': 'node_modules/rxjs'
    },
    // packages tells the System loader how to load when no filename and/or no extension
    packages: {
        app: {
            main: './main.js',
            defaultExtension: 'js'
        },
        rxjs: {
            defaultExtension: 'js'
        }
    }  

package.json中的代码段

 "devDependencies": {
"concurrently": "^3.0.0",
"lite-server": "^2.2.2",
"typescript": "^2.0.3",
"typings": "^1.4.0",
"@types/jasmine": "^2.5.35",
"angular-cli": "1.0.0-beta.17",
"codelyzer": "1.0.0-beta.0",
"jasmine-core": "^2.5.2",
"jasmine-spec-reporter": "2.7.0",
"karma": "1.3.0",
"karma-chrome-launcher": "^2.0.0",
"karma-jasmine": "^1.0.2",
"karma-remap-istanbul": "^0.2.1",
"protractor": "4.0.9",
"ts-node": "1.4.1",
"tslint": "^3.15.1",
"gulp": "3.9.1",
"gulp-clean-css": "2.0.13",
"gulp-concat": "2.6.0",
"gulp-plumber": "1.1.0",
"gulp-typescript": "3.0.2",
"gulp-uglify": "2.0.0",
"gulp-tslint": "6.1.2",
"gulp-sourcemaps": "2.1.1",
"systemjs": "0.19.39",
"systemjs-builder": "0.15.32"
}

nodejs版本:6.2.0

npm版本:3.10.8

任何建议将不胜感激

推荐答案

您需要在app.module中提供用户服务，并删除app.component中的@Inject和providers条目:

You need to provide the user service in your app.module and remove the @Inject and the providers entry in the app.component:

app.module.ts

import { NgModule } from '@angular/core';
import { HttpModule } from '@angular/http';
import { BrowserModule } from '@angular/platform-browser';
import { AppComponent }   from './app.component';
//Add your UserService import here

@NgModule({
    imports: [
        BrowserModule,
        HttpModule],
  declarations: [ AppComponent ],
  bootstrap:    [ AppComponent ],
  providers:    [ UserService ]
})
export class AppModule { }

app.component.ts

import { Component, OnInit, Inject } from '@angular/core';
import { UserService } from './services/user.service';
import { User } from './models/user';

@Component({
    selector: 'my-app',
    templateUrl: 'app/app.component.html'
})
export class AppComponent implements OnInit {
    user: User;

    constructor(
        private _userService: UserService) {
    }
    getCurrentUser() {
        this._userService.getCurrentUser()
            .subscribe(user => this.user = user);
    }
    ngOnInit() {
        this.getCurrentUser();
    }
}

通过这种方式，UserService依赖项由注入器管理，并且您不直接向组件提供服务(此行为自最终发行版以来已被废弃或完全删除，不知道 ).

this way, UserService dependencies are managed by the injector and you don't provide the service directly to your component (this behaviour is deprecated or even removed, don't know since final release).

这篇关于Angular 2-无法读取未定义的属性"get"(http未定义)的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！