如何解决无法解决角度上的所有参数错误

Question

刚刚开始使用角度2，并遇到我的第一个错误。我试图创建一个从服务器获取数据的服务，但我得到这个错误

Error: Can't resolve all parameters for CourseService: (?). at SyntaxError.ZoneAwareError (http:……}

这是服务代码引发错误的应用程序/场/ courses.service.ts

import { Http } from '@angular/http'; 

export class CourseService { 

    private _courses : Object[]; 

    public get courses() : Object[] { 
     return this._courses; 
    } 

    public set courses(v : Object[]) { 
     this._courses = v; 
    } 

    constructor(private http: Http) { 
     http.get("https://jsonplaceholder.typicode.com/posts").subscribe(data => { 
      this._courses = data.json(); 
     }); 
    } 
} 

这服务应该在app /课程中使用/ courses.component.ts

import { Component } from '@angular/core' 
import { CourseService } from "app/courses/course.service"; 

@Component({ 
    selector: 'courses', 
    providers: [CourseService], 
    templateUrl: './courses.component.html', 
    styleUrls: ['./courses.component.css'] 
}) 

export class CoursesComponent { 
    title : string = "The title of the Course"; 
    courses : Object[]; 

    constructor(private courseService: CourseService) { 
     console.log("hello"); 
     this.courses = courseService.courses; 
    } 
} 

和app.module包含

.... 
.... 
import { AppComponent } from './app.component'; 
import { CoursesComponent } from './courses/courses.component'; 
import { CourseService } from "./courses/course.service"; 

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

Answer 1

在导出类之前放@Injectable（）。
@Injectable() lets Angular know that a class can be used with the dependency injector.