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我希望这是有道理的。我决定改变我的一些服务的工作方式仅仅是因为订阅响应和在不同的视图中处理创建、更新和删除变得有点麻烦。所以我决定做一个这样的通用服务：

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { map } from 'rxjs/operators';

import { environment } from '@environments/environment';
import { Resource } from '../models/resource';
import { ToastrService } from 'ngx-toastr';
import { BehaviorSubject } from 'rxjs';

@Injectable({
    providedIn: 'root',
})
export class DataService<T extends Resource> {
    items: BehaviorSubject<T[]>;

    constructor(private endpoint: string, private http: HttpClient, private toastr: ToastrService) {
        this.items = new BehaviorSubject<T[]>([]);
    }

    initialize(feedId: number) {
        return this.http.get<T[]>(`${environment.apiUrl}/feeds/${feedId}/${this.endpoint}`).pipe(
            map(response => {
                console.log(this.endpoint, response);
                this.items.next(response);
                return response;
            }),
        );
    }

    get(id: number) {
        return this.http.get<T>(`${environment.apiUrl}/${this.endpoint}/${id}`);
    }

    create(filter: T) {
        return this.http.post<T>(`${environment.apiUrl}/${this.endpoint}`, filter).pipe(
            map((response: any) => {
                const message = response.message;
                const item = response.model;

                let items = this.items.value;
                items.push(item);

                this.emit(items, message);

                return response.model;
            }),
        );
    }

    update(filter: T) {
        return this.http.put<T>(`${environment.apiUrl}/${this.endpoint}`, filter).pipe(
            map((response: any) => {
                const message = response.message;
                const item = response.model;

                let items = this.items.value;
                this.remove(items, filter.id);
                items.push(item);

                this.emit(items, message);

                return response.model;
            }),
        );
    }

    delete(id: number) {
        return this.http.delete<string>(`${environment.apiUrl}/${this.endpoint}/${id}`).pipe(
            map((response: any) => {
                let items = this.items.value;
                items.forEach((item, i) => {
                    if (item.id !== id) return;
                    items.splice(i, 1);
                });

                this.emit(items, response);

                return response;
            }),
        );
    }

    private remove(items: T[], id: number) {
        items.forEach((item, i) => {
            if (item.id !== id) return;
            items.splice(i, 1);
        });
    }

    private emit(items: T[], message: string) {
        this.items.next(items);
        this.toastr.success(message);
    }
}

这个服务背后的想法是，initialize方法只被调用一次，当它被调用时，你可以看到它将响应映射到服务本身内的items数组。然后，当执行创建、更新或删除时，更改的是该数组。

这将（理论上）允许任何组件订阅items数组以更新任何更改。

因此，我有一些“扩展”此服务的服务，例如：

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';

import { Filter } from '@models';
import { DataService } from './data.service';
import { ToastrService } from 'ngx-toastr';

@Injectable({
    providedIn: 'root',
})
export class FilterService extends DataService<Filter> {
    constructor(httpClient: HttpClient, toastr: ToastrService) {
        super('filters', httpClient, toastr);
    }
}

到目前为止，一切都很好。所以，我的问题是：我是否必须调用初始化方法并调用订阅？

例如，目前我有这个组件：

import { Component, OnInit, Input } from '@angular/core';
import { first } from 'rxjs/operators';

import { FilterService } from '@services';
import { NgAnimateScrollService } from 'ng-animate-scroll';

@Component({
    selector: 'app-feed-filters',
    templateUrl: './filters.component.html',
    styleUrls: ['./filters.component.scss'],
})
export class FiltersComponent implements OnInit {
    @Input() feedId: number;
    displayForm: boolean;

    constructor(private animateScrollService: NgAnimateScrollService, private filterService: FilterService) {}

    ngOnInit() {
        this.initialize();
    }

    navigateToForm() {
        this.displayForm = true;
        this.animateScrollService.scrollToElement('filterSave');
    }

    private initialize(): void {
        this.filterService
            .initialize(this.feedId)
            .pipe(first())
            .subscribe(() => {});
    }
}

正如您在私有方法中看到的pipe那样first，subscribe如果我想从那里得到结果，我会这样做。在我的“子”组件中，我有这个：

import { Component, OnInit, Input, Output, EventEmitter } from '@angular/core';
import { first } from 'rxjs/operators';

import { Filter } from '@models';
import { NgbModal } from '@ng-bootstrap/ng-bootstrap';
import { ConfirmationDialogComponent } from '@core';
import { FilterService } from '@services';
import { FiltersSaveComponent } from './filters-save.component';

@Component({
    selector: 'app-filters',
    templateUrl: './filters.component.html',
    styleUrls: ['./filters.component.scss'],
})
export class FiltersComponent implements OnInit {
    filters: Filter[];

    constructor(private modalService: NgbModal, private filterService: FilterService) {}

    ngOnInit() {
        this.filterService.items.subscribe(filters => (this.filters = filters));
    }

    openModal(id: number) {
        const modalRef = this.modalService.open(ConfirmationDialogComponent);
        modalRef.componentInstance.message = 'Deleting a filter is irreversible. Do you wish to continue?';
        modalRef.result.then(
            () => {
                this.filterService.delete(id);
            },
            () => {
                // Do nothing
            },
        );
    }

    openSaveForm(filter: Filter) {
        const modalRef = this.modalService.open(FiltersSaveComponent);
        modalRef.componentInstance.feedId = filter.feedId;
        modalRef.componentInstance.filterId = filter.id;
        modalRef.componentInstance.modal = true;
    }
}

如您所见，我从filterService订阅了items数组。所以，在我的父控制器中，我认为我实际上不需要订阅，但如果我删除它就不起作用。

我以为我可以做类似的事情：

private initialize(): void {
    this.filterService.initialize(this.feedId);
}

代替

private initialize(): void {
    this.filterService
        .initialize(this.feedId)
        .pipe(first())
        .subscribe(() => {
            // I don't need this
        });
}

我做错了什么，还是我必须这样做？我希望我解释了自己:)

4

1 回答 1

2

您必须调用subscribe任何请求方法HttpClient以发送请求。返回一个冷的HttpClient可观察对象，这意味着它在订阅它之前不会运行（与立即开始运行的热可观察对象相反）。

此外，来自 the 的 observableHttpClient只会发出一个值，即响应，这意味着不需要将其传递给first它。您的最终逻辑将如下所示：

this.filterService.initialize(this.feedId).subscribe(() => undefined);

或者，您可以在使用服务的地方订阅，而不是订阅，DataService然后您的呼叫将如下所示：

this.filterService.initialize(this.feedId);

的一个好处HttpClient是它们返回的可观察对象将永远不会再次发出，因此无需跟踪订阅并在以后关闭它。

于 2019-09-16T17:18:24.350 回答