等待异步函数在 Angular 中完成

Question

所以我在 Angular 中开发一个新组件，在 ngOninit 中我有以下异步函数...

This.getUserProfile 需要在我调用 this.getPrivateGroup() 之前完成，并且 this.getPrivateGroup() 需要在我调用 this.loadGroupPosts() 之前完成。我知道我可以在异步请求的回调中编写这些函数，但我想知道是否有办法将其保留在 ngOnInit 中以使其更清洁？

有人有想法吗？

ngOnInit() {

    this.getUserProfile();

    // my-workplace depends on a private group and we need to fetch that group and edit
    // the group data before we proceed and get the group post
    if (this.isItMyWorkplace) {
      this.getPrivateGroup();
    }
    this.loadGroupPosts();
  }

getUserProfile() {
    this._userService.getUser()
      .subscribe((res) => {
        this.user = res.user;
        console.log('log user', this.user);
        this.profileImage = res.user['profile_pic'];
        this.profileImage = this.BASE_URL + `/uploads/${this.profileImage}`;
      }, (err) => {
        this.alert.class = 'alert alert-danger';
        if (err.status === 401) {
          this.alert.message = err.error.message;
          setTimeout(() => {
            localStorage.clear();
            this._router.navigate(['']);
          }, 3000);
        } else if (err.status) {
          this.alert.class = err.error.message;
        } else {
          this.alert.message = 'Error! either server is down or no internet connection';
        }
      });
  }



getPrivateGroup() {
    console.log('user check', this.user);
    this.groupService.getPrivateGroup(`${this.user.first_name}${this.user.last_name}`)
      .subscribe((group) => {
          console.log('received response', group)
    })
  }

 // !--LOAD ALL THE GROUP POSTS ON INIT--! //
  loadGroupPosts() {
    this.isLoading$.next(true);

    this.postService.getGroupPosts(this.group_id)
      .subscribe((res) => {
        // console.log('Group posts:', res);
        this.posts = res['posts'];
        console.log('Group posts:', this.posts);
        this.isLoading$.next(false);
        this.show_new_posts_badge = 0;
      }, (err) => {
        swal("Error!", "Error while retrieving the posts " + err, "danger");
      });
  }
  // !--LOAD ALL THE GROUP POSTS ON INIT--! //

Answer 1

一种方法是，返回 Observable 而不是订阅 getPrivateGroup()

getPrivateGroup() {
    console.log('user check', this.user);
    return this.groupService.getPrivateGroup(`${this.user.first_name}${this.user.last_name}`)

  }

然后，订阅你想要链接的数据this.loadGroupPosts()

     if (this.isItMyWorkplace) {
          this.getPrivateGroup().subscribe(group => {
          this.group = group; //you probably want to assign the group data
          this.loadGroupPosts()});
        }

Answer 2

您可以通过async/await 使用基本承诺。

async ngOnInit() {

    await this.getUserProfile(); // <-- 1. change

    // my-workplace depends on a private group and we need to fetch that group and edit
    // the group data before we proceed and get the group post
    if (this.isItMyWorkplace) {
      this.getPrivateGroup();
    }
    this.loadGroupPosts();
  }

async getUserProfile() {
    this._userService.getUser()
      .subscribe((res) => {
        this.user = res.user;
        console.log('log user', this.user);
        this.profileImage = res.user['profile_pic'];
        this.profileImage = this.BASE_URL + `/uploads/${this.profileImage}`;
        return true; // <-- this
      }, (err) => {
        this.alert.class = 'alert alert-danger';
        if (err.status === 401) {
          this.alert.message = err.error.message;
          setTimeout(() => {
            localStorage.clear();
            this._router.navigate(['']);
          }, 3000);
        } else if (err.status) {
          this.alert.class = err.error.message;
        } else {
          this.alert.message = 'Error! either server is down or no internet connection';
        }
        throw err;
      });

}

Answer 3

您可以改为利用 RxJS 并使用类似这样的 switchMap（未检查语法）：

getData(): Observable<string[]> {
  return this._userService.getUser()
    .pipe(
      switchMap(userInfo=> {
         return this.getPrivateGroup();
      }),
      catchError(this.someErrorHandler)
    );
}