Angular 6如何管道http调用

鲁斯塔姆·加涅涅夫（Rustam Ganeyev）

我有一个HTTP服务，该服务使用HttpClient进行API调用：

//provider.service.ts
export interface Lesson {
    id?: number,
    name: string,
    type: LessonType,
    teacher_data: string,
    student_data: string
}

export class ProviderService {
    constructor(private http: HttpClient) {}

    postLesson(form): Observable<Lesson> {        
        const body = this.getFormUrlEncoded(form.value);
        return this.http.post<Lesson>('/api/lesson/', body, this.postHttpOptions);
    }
}

我有一个使用此ProviderService的组件，如下所示：

onSubmit():void {
    this.providerService.createLesson(lessonForm).subscribe(result=> {
        console.log(result);
        //do my stuff
      });
    }
  }

它工作正常，一切都很好。现在，我想创建一个LessonService，以使所有http调用都通过该服务。它会缓存结果，发出更改等。

我是这样写的：

//updated lessons.component.ts
    onSubmit():void {
        this.LessonsService.createLesson(this.lessonForm).subscribe(result=> {
            console.log(result);
            //do my stuff
        });
    }

//lessons.service.ts
export class LessonsService {
    constructor(private http: ProviderService) {}

    @Output() lessonChange: EventEmitter<Lesson> = new EventEmitter();

    public createLesson(form): Observable<Lesson> {
        let observable = this.http.postLesson(form);
        observable.pipe(
            map(result => {
                //this code is not executed, I do not understand why                
                this.lessonChange.emit(result);
                return result;
            })
        );    
        return observable;
  }
}

当我从HTTP提供程序获取结果时，我想发出一个事件。我做错了什么？

巴鲁克

有两种方法可以执行此操作，一种是将放入pipe变量声明中，然后使用tap代替map。

export class LessonsService {
    @Output() lessonChange: EventEmitter<Lesson> = new EventEmitter();

    public createLesson(form): Observable<Lesson> {
        let observable = this.http.postLesson(form).pipe(
            tap(result => {
                //this code is not executed, I do not understand why                
                this.lessonChange.emit(result);
                return result;
            })
        );    
        return observable;
  }
}

另一种方法是创建对变量的订阅

export class LessonsService {
    @Output() lessonChange: EventEmitter<Lesson> = new EventEmitter();

    public createLesson(form): Observable<Lesson> {
        let observable = this.http.postLesson(form);
        observable.subscribe(result => {
            //this code is not executed, I do not understand why                
            this.lessonChange.emit(result);
            return result;
        );    
        return observable;
  }
}

我个人会选择后者，这样您可以确保仅在成功时才发出事件。

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