我该如何解决 - “订阅”类型上不存在“那么”属性

Question

I wrote PUT and DELETE methods inside their functions ("editForm" and "deleteForm" respectively).

I wanted to display setAlert() function after each request successfully completes. therefore, I used .then() method and it works perfectly inside editForm function as you can see it below.

but when I do the same for deleteForm , .then() method does not works, because it says: " Property 'then' does not exist on type 'Subscription' ". So how can I solve this?

Here is my component.ts file:

import { Component, OnInit, OnDestroy } from '@angular/core';
import { ActivatedRoute, Router } from '@angular/router';
import { FormService } from './forms.service';
import { HttpClient } from '@angular/common/http';
import { alert } from './alert';

@Component({
  selector: 'app-forms',
  templateUrl: './forms.component.html',
  styleUrls: ['./forms.component.css']
})


export class FormsComponent implements OnInit {

  alert: alert;
  id: any;
  posts: any;

  constructor(public formService: FormService ,private route: ActivatedRoute,
    private router: Router, private http: HttpClient) { }



  ngOnInit() {
    this.id=this.route.snapshot.params['id'];
    this.alert = new alert();

    this.posts = this.formService.getForms(this.id).subscribe(
      (forms: any) => {
        this.formService.form = forms[0];
      }
    );
  }

  editPost() {
    this.formService.editForm().then((res:any) => {
      this.formService.alert.setAlert("Post has been successfully saved !");
    })
  }

  deletePost() {
    this.formService.deleteForm().subscribe(
      data  => {
        console.log("DELETE Request is successful ", data);
      },
      error  => {
        console.log("Error", error);
      }
    ).then(() => {
      this.formService.alert.setAlert("Post has been successfully deleted !");
    })
  }

}

Here is my service.ts file:

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { form } from './form-interface';
import { alert } from './alert';


@Injectable({
    providedIn: 'root'
}) 

export class FormService {

  formsUrl = "https://jsonplaceholder.typicode.com/posts";
  form: form = {
      id: 0,
      userId: 0,
      title: '',
      body: ''
  };
  alert: alert;


    constructor(private http: HttpClient) { 
      this.alert = new alert();
    }

    getForms(id) {
            return this.http.get('https://jsonplaceholder.typicode.com/posts'
            + "?id=" + id)
    }

    editForm() {
        return fetch(this.formsUrl + "/" + this.form.id, {
          method: 'PUT',
          body: JSON.stringify(this.form),
          headers: {
            "Content-type": "application/json; charset=UTF-8"
          }
        })
        .then(response => response.json())
    }

    deleteForm() {
        return this.http.delete(this.formsUrl + "/" + this.form.id);
      }

}

Answer 1

because http returns observable not promise. Use .subscribe here.It will solve your problem

Answer 2

The editform method uses JavaScript fetch api to call the service, which returns the promise so then method works there. In deleteForm method, you are making a service call using angular HttpClient which returns observable. instead of using then you should use subscribe method

deleteForm() {
        return this.http.delete(this.formsUrl + "/" + this.form.id);
}

In your component.ts

 deletePost() {
    this.formService.deleteForm().subscribe(
      data  => {
        console.log("DELETE Request is successful ", data);
        this.formService.alert.setAlert("Post has been successfully deleted !");
      },
      error  => {
        console.log("Error", error);
      }
    )
  }

Answer 3

You can use message when you get a proper response while you get the response in subscribe method and call alert into it Like below

deletePost() {
this.formService.deleteForm().subscribe(
  data  => {
    console.log("DELETE Request is successful ", data);
    this.formService.alert.setAlert("Post has been successfully deleted !");
  },
  error  => {
    console.log("Error", error);
  }
))

}