app.service.ts

import { Injectable, ChangeDetectorRef } from '@angular/core';
import { MediaMatcher } from '@angular/cdk/layout';

@Injectable()
export class AppService {

    private _mobileQueryListener    : () => void;
    mobileQuery                     : MediaQueryList;

    currentUser: any;

    constructor(changeDetectorRef: ChangeDetectorRef, media: MediaMatcher) {
        this.mobileQuery = media.matchMedia('(max-width: 768px)');
        this._mobileQueryListener = () => changeDetectorRef.detectChanges();
        this.mobileQuery.addListener(this._mobileQueryListener);
    }

    initService() {
        
    }

    getViewMode() {
        if( /Android|webOS|iPhone|iPad|iPod|BlackBerry|IEMobile|Opera Mini/i.test(navigator.userAgent) ) {
            return true;
        } else {
            return this.mobileQuery.matches;
        }
    }

    ngOnDestroy(): void {
        this.mobileQuery.removeListener(this._mobileQueryListener);
    }
}