javascript - 使用事件发射器和服务进行跨组件通信的角度异步调用

问题描述

无法将从 subscribe 方法接收到的值存储在模板变量中。

照片细节组件

import { Component, OnInit, Input } from "@angular/core";
import { PhotoSevice } from "../photo.service";
import { Photo } from "src/app/model/photo.model";

@Component({
  selector: "app-photo-detail",
  templateUrl: "./photo-detail.component.html",
  styleUrls: ["./photo-detail.component.css"]
})
export class PhotoDetailComponent implements OnInit {

  url: string;

  constructor(private photoService: PhotoSevice) {
    this.photoService.photoSelected.subscribe(data => {
      this.url = data;
      console.log(this.url);
    });
    console.log(this.url);
  }

  ngOnInit() {

  }
}

外部console.log 给出未定义，视图中没有呈现任何内容，但在subscibe 方法内我可以看到该值。那么，我如何在我的视图中显示它？

照片组件

import { Component, OnInit } from "@angular/core";
import { ActivatedRoute, Params, Router } from "@angular/router";
import { FnParam } from "@angular/compiler/src/output/output_ast";
import { AlbumService } from "../service/album.service";
import { Photo } from "../model/photo.model";
import { PhotoSevice } from "./photo.service";

@Component({
  selector: "app-photos",
  templateUrl: "./photos.component.html",
  styleUrls: ["./photos.component.css"]
})
export class PhotosComponent implements OnInit {
  selectedAlbumId: string;
  photoList: Photo[] = [];
  photoSelected: Photo;
  isLoading: Boolean;
  constructor(
    private rout: ActivatedRoute,
    private albumService: AlbumService,
    private router: Router,
    private photoService: PhotoSevice
  ) { }

  ngOnInit() {
    this.isLoading = true;
    this.rout.params.subscribe((params: Params) => {
      this.selectedAlbumId = params["id"];
      this.getPhotos(this.selectedAlbumId);
    });
  }

  getPhotos(id: string) {
    this.albumService.fetchPhotos(this.selectedAlbumId).subscribe(photo => {
      this.photoList = photo;
      this.isLoading = false;
    });
  }

  displayPhoto(url: string, title: string) {

    console.log(url);
    this.photoService.photoSelected.emit(url);
    this.router.navigate(["/photo-detail"]);
  }
}

请解释一下这是如何工作的以及如何解决它，以便我可以在模板视图中存储和显示从订阅和异步调用接收到的值。

这是两个组件的视图---

photo.component.html

<div *ngIf="isLoading">
  <h3>Loading...</h3>
</div>

<div class="container" *ngIf="!isLoading">
  <div class="card-columns">
    <div *ngFor="let photo of photoList" class="card">
      <img
        class="card-img-top"
        src="{{ photo.thumbnailUrl }}"
        alt="https://source.unsplash.com/random/300x200"
      />
      <div class="card-body">
        <a
          class="btn btn-primary btn-block"
          (click)="displayPhoto(photo.url, photo.title)"
          >Enlarge Image</a
        >
      </div>
    </div>
  </div>
</div>

照片细节.component.ts

<div class="container">
  <div class="card-columns">
    <div class="card">
      <img class="card-img-top" src="{{ url }}" />
    </div>
  </div>
</div>

照片服务.ts

import { Injectable } from "@angular/core";
import { EventEmitter } from "@angular/core";

@Injectable({ providedIn: "root" })
export class PhotoSevice {
  photoSelected = new EventEmitter();
 // urlService: string;
}

这是我的 github 存储库的链接，我将代码保留在注释中，并在那里使用了不同的方法。如果您检查相册组件，我还订阅了 http 请求并在相册组件的模板变量中分配了值。也有值作为未定义的 oustide subscibe 方法出现，但我可以在模板中访问它。

https://github.com/Arpan619Banerjee/angular-accelerate

这是专辑组件和服务的详细信息， 请将此与事件发射器案例进行比较并解释一下有什么区别 --专辑.component.ts

import { Component, OnInit } from "@angular/core";
import { AlbumService } from "../service/album.service";
import { Album } from "../model/album.model";

@Component({
  selector: "app-albums",
  templateUrl: "./albums.component.html",
  styleUrls: ["./albums.component.css"]
})
export class AlbumsComponent implements OnInit {
  constructor(private albumService: AlbumService) {}
  listAlbums: Album[] = [];
  isLoading: Boolean;

  ngOnInit() {
    this.isLoading = true;
    this.getAlbums();
  }

  getAlbums() {
    this.albumService.fetchAlbums().subscribe(data => {
      this.listAlbums = data;
      console.log("inside subscibe method-->" + this.listAlbums); // we have data here
      this.isLoading = false;
    });
    console.log("outside subscribe method----->" + this.listAlbums); //empty list==== but somehow we have the value in the view , this doesn t work
    //for my photo and photo-detail component.
  }
}

相册.component.html

<div *ngIf="isLoading">
  <h3>Loading...</h3>
</div>
<div class="container" *ngIf="!isLoading">
  <h3>Albums</h3>
  <app-album-details
    [albumDetail]="album"
    *ngFor="let album of listAlbums"
  ></app-album-details>
</div>

专辑.service.ts

import { Injectable } from "@angular/core";
import { HttpClient, HttpParams } from "@angular/common/http";
import { map, tap } from "rxjs/operators";
import { Album } from "../model/album.model";
import { Observable } from "rxjs";
import { UserName } from "../model/user.model";

@Injectable({ providedIn: "root" })
export class AlbumService {
  constructor(private http: HttpClient) {}
  albumUrl = "http://jsonplaceholder.typicode.com/albums";
  userUrl = "http://jsonplaceholder.typicode.com/users?id=";
  photoUrl = "http://jsonplaceholder.typicode.com/photos";

  //get the album title along with the user name
  fetchAlbums(): Observable<any> {
    return this.http.get<Album[]>(this.albumUrl).pipe(
      tap(albums => {
        albums.map((album: { userId: String; userName: String }) => {
          this.fetchUsers(album.userId).subscribe((user: any) => {
            album.userName = user[0].username;
          });
        });
        // console.log(albums);
      })
    );
  }

  //get the user name of the particular album with the help of userId property in albums
  fetchUsers(id: String): Observable<any> {
    //let userId = new HttpParams().set("userId", id);
    return this.http.get(this.userUrl + id);
  }

  //get the photos of a particular album using the albumId
  fetchPhotos(id: string): Observable<any> {
    let selectedId = new HttpParams().set("albumId", id);
    return this.http.get(this.photoUrl, {
      params: selectedId
    });
  }
}

如评论中所述，我已在偶数发射器中添加了控制台日志，这是我得到的预期行为。

标签： javascriptangularasynchronouscomponentsangular-event-emitter

javascript - 使用事件发射器和服务进行跨组件通信的角度异步调用

问题描述

解决方案

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