How to return object from service to component in angular

问题

I want to access particular json in ngOninit. So i have id on click in edit button and with the help of that id i am getting complete object from database like form name , form json which etc. So from the service i want to return that json to ngOninit.

Here is service.

    GetFormById (id: number) {
    return this.httpClient.get<FormTemplate[]>(this.API_URL + 
    "GetFormTemplate/" + id).subscribe(data => {
      console.log(data);
      return data;
    });
    }

In console i am getting complete object from database which i have save.

Here is component

    ngOnInit() {
    const id = this.route.snapshot.paramMap.get('id');
    var json = this.dataService.GetFormById(+id);
    }

like how can i get json in ngOnInit.

Edit

ngOnInit() {
const id = this.route.snapshot.paramMap.get('id');
this.dataService.GetFormById(+id).subscribe(response => {
  console.log(response);
  const temp = response['TemplateJson'];
     })

initJq();
  var formData = '[{"type":"header","subtype":"h1","label":"Inquiry"},{"type":"paragraph","subtype":"p","label":"Paragraph content"},{"type":"text","label":"First name","name":"text - 1554220470561","value":"Vipul","subtype":"text"},{"type":"date","label":"Date Field","className":"form - control","name":"date - 1554220484446","value":"2019 - 04 - 25"},{"type":"button","label":"Send Inquiry","subtype":"button","className":"btn btn - primary","name":"button - 1554220480284","style":"primary"}]';

  this.formBuilder = (<any>jQuery('.build-wrap')).formBuilder({ formData });

 // Sample code to handle promise to get for data on page load directly
  this.formBuilder.promise.then(formBuilder => {
    console.log(formBuilder.formData);
  });
}

like whatever json i got in temp i want to pass it in var formData.

回答1:

This is not how you should subscribe from observables. You should read up the documentation/tutorial when it comes to handling asynchronous operations (such as HTTP requests). Meanwhile, this is how we can fix your issue.

On your service,

GetFormById (id: number) {
  return this.httpClient.get<FormTemplate[]>(`${this.API_URL}GetFormTemplate/${id}`);
}

On your component.ts, we return the observable value by calling the subscribe() method.

ngOnInit() {
  const id = this.route.snapshot.paramMap.get('id');
  this.dataService.GetFormById(id).subscribe(response => {
    console.log(response);
    const templateObj = response.TempleteJson;
  })
}

回答2:

You don't subscribe to the Observable in the service class, but instead in the component:

In the service, just return the Observable from your service method:

GetFormById (id: number): Observable<FormTemplate[]>{
    return this.httpClient.get<FormTemplate[]>(this.API_URL + "GetFormTemplate/" + id);
}

In the component you subscribe to the Observable returned by the service method:

ngOnInit() {
  const id = this.route.snapshot.paramMap.get('id');
  this.dataService.GetFormById(+id).subscribe(data => {
    console.log(data);
  });
}

回答3:

Don't subscribe inside service, subscribe insdie componet onitit.

GetFormById (id: number) {
    return this.httpClient.get<FormTemplate[]>(this.API_URL + "GetFormTemplate/" + id);
}

ngOnInit() {
    const id = this.route.snapshot.paramMap.get('id');
    this.dataService.GetFormById(+id).subscribe(data => {
      console.log(data);
    })
}

来源：https://stackoverflow.com/questions/55605849/how-to-return-object-from-service-to-component-in-angular