How to Show spinner for every HTTP requests in ang

问题:

i am new to angular 5 . How to code a common function to show spinner for every HTTP request in angular 5.Please help me to implement this.

回答1:

You can use Angular HttpInterceptor to show a spinner for all your requests, Here's a good medium article on how to implement an http interceptor

Also, you will have to create a spinner service/module and inject it in your http interceptor. Finally, in your intercept method you can use the finally rxJs method to stop your spinner. Here's a simple implementation:

  intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
    this.spinnerService.start();
    return next.handle(req).finally(res => this.spinnerService.stop() );
  }

Enjoy !

Bonus: Here's a spinner service implementation example

回答2:

This has nothing to do with HttpClient or HTTP Requests. It is a question of how to handle asynchronous calls in general (HTTP or not).

You should have

<div class="spinner" *ngIf="loading"; else showWhenLoaded"><div>
<ng-template #showWhenLoaded>
    <div>Your Content</div>
</ng-template>

and in the ts-file:

loading: boolean = true;

methodToTriggerRequest() {
    this.loading = true;
    this.http.get(...).subscribe(response => {
        if (resposnseNotAnError(response)) {this.loading = false}
    })
}

回答3:

You can create a service and then publish events to it while in the root level of the application subscribed to it. Let me explain.

broadcast.service.ts (this is your service)

import { Injectable } from '@angular/core';

import { Subject } from 'rxjs/Subject';
import { Subscription } from 'rxjs/Subscription';

import 'rxjs/add/operator/filter'
import 'rxjs/add/operator/map'

/**
 * This class acting as event service bus for the entire app.
 * No Need to register the class as this registered in the root level.
 * Can just inject to componets.
 */
@Injectable()
export class BroadcastService {

    private _handler: Subject<Message> = new Subject<Message>();

    broadcast(type: string, payload: any = null) {
        this._handler.next({ type, payload });
    }

    subscribe(type: string, callback: (payload: any) => void): Subscription {
        return this._handler
            .filter(message => message.type === type)
            .map(message => message.payload)
            .subscribe(callback);
    }
}

interface Message {
    type: string;
    payload: any;
}

Then in you can publish and subscribe to events like this:

your service level:

this.broadcastService.broadcast('PROGRESS_START');

In your app component level:

this.broadcastService.subscribe('PROGRESS_START', ()=>{
  //hit when you start http call
  this.myLoader = true;
});

finally in app.component.html:

<div *ngIf="myLoader">
 <!--YOUR LOADER SHOULD GO HERE-->
</div>
<router-outlet></router-outlet>

This is very generic loosely coupled way to implement any loader you want.

回答4:

Source Link

Create a service

//loader.service.ts
import { Injectable } from '@angular/core';
import { BehaviorSubject } from 'rxjs';

@Injectable({
  providedIn: 'root'
})
export class LoaderService {

  public isLoading = new BehaviorSubject(false);
  constructor() { }
}

Create Loader Interceptor

    // loader.interceptors.ts
    import { Injectable } from '@angular/core';
    import {
        HttpErrorResponse,
        HttpResponse,
        HttpRequest,
        HttpHandler,
        HttpEvent,
        HttpInterceptor
    } from '@angular/common/http';
    import { Observable } from 'rxjs';
    import { LoaderService } from './loader.service';

    @Injectable()
    export class LoaderInterceptor implements HttpInterceptor {
        private requests: HttpRequest<any>[] = [];

        constructor(private loaderService: LoaderService) { }

        removeRequest(req: HttpRequest<any>) {
            const i = this.requests.indexOf(req);
            if (i >= 0) {
                this.requests.splice(i, 1);
            }
            this.loaderService.isLoading.next(this.requests.length > 0);
        }

        intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {

            this.requests.push(req);
            console.log("No of requests--->" + this.requests.length);
            this.loaderService.isLoading.next(true);
            return Observable.create(observer => {
                const subscription = next.handle(req)
                    .subscribe(
                        event => {
                            if (event instanceof HttpResponse) {
                                this.removeRequest(req);
                                observer.next(event);
                            }
                        },
                        err => {
                            alert('error returned');
                            this.removeRequest(req);
                            observer.error(err);
                        },
                        () => {
                            this.removeRequest(req);
                            observer.complete();
                        });
                // remove request from queue when cancelled
                return () => {
                    this.removeRequest(req);
                    subscription.unsubscribe();
                };
            });
        }
    }

Now create a loader component then add in the app component

  //loader.interceptor.ts
  import { Component, OnInit } from '@angular/core';
  import { LoaderService } from '../loader.service';

  @Component({
    selector: 'app-loading',
    templateUrl: './loading.component.html',
    styleUrls: ['./loading.component.css']
  })
  export class LoaderComponent implements OnInit {

    loading: boolean;
    constructor(private loaderService: LoaderService) {
      this.loaderService.isLoading.subscribe((v) => {
        console.log(v);
        this.loading = v;
      });
    }
    ngOnInit() {
    }

  }

回答5:

In Angular's interceptor I have used "do" operator.

intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {

    // handler for both success and fail response
    const onReqFinish = (event: HttpEvent<any>) => {
      if (event.type === 4) {
        this.onXhrFinish();
      }
    };

    this.onXhrStart();

    return next.handle(req)
     .do(
       onReqFinish,
       onReqFinish
     );
}

onXhrStart function shows a loader and onXhrFinish hides it.

Entire, working source code and demo are here