【发布时间】：2020-03-22 05:42:22
【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方法中我可以看到值。那么，我怎样才能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"]);
}
}
请解释一下它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>
photo-detail.component.ts
<div class="container">
<div class="card-columns">
<div class="card">
<img class="card-img-top" src="{{ url }}" />
</div>
</div>
</div>
photo.service.ts
import { Injectable } from "@angular/core";
import { EventEmitter } from "@angular/core";
@Injectable({ providedIn: "root" })
export class PhotoSevice {
photoSelected = new EventEmitter();
// urlService: string;
}
这里是我的 github 存储库的链接，我将代码保存在 cmets 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 subscibe 方法出现，但我可以在模板中访问它。
https://github.com/Arpan619Banerjee/angular-accelerate
这里是相册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- albums.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.
}
}
albums.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>
album.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
});
}
}
我已按照 cmets 中的说明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。
【问题讨论】：
-
可以显示
PhotoSevice吗？在这种情况下，您不需要事件发射器。你需要一个Subject。 -
是的，我已经附加了照片服务，是的，我通过简单地在照片服务中定义一个变量并将其设置在照片组件中来满足要求，然后我从我的照片细节组件中访问它。有效。请检查我的问题一次，我添加了更多细节。请将该行为与 http 调用和事件发射器进行比较，并向我解释发生了什么。
-
我已经发布了答案。将来请尝试从问题中删除代码的非必要部分。
标签： javascript angular asynchronous components angular-event-emitter