public isValid() : boolean {
        this.changeDetector.detectChanges();

        return this.invoiceForm.valid
            && this.invoice.items.length !== 0
            && this.itemsArray.valid;
    }

 this.lib.getLibrary().subscribe((songs: Song[]) => {
     this.songs = songs;
     this.cd.detectChanges();
 });

 this.iconSub = this.fonticon.getCss(collectionName).subscribe((data: any) => {
   this.value = data[className];
   this._ref.markForCheck();
 });

 onAppStoreUpdate() {
     this.changeDetectorRef.markForCheck();
 }

 onAppStoreUpdate() {
     this.issues = this.appStore.getState().issues;
     this.changeDetectorRef.markForCheck();
 }

 private onForceDetection(){
     this.ref.markForCheck();
     console.log('cd completed')
 }

 setInterval(() => {
     this.ref.markForCheck();
 }, intervalMsec);

 this.invoiceService.getInvoice(this.id).subscribe((invoice:Invoice) => {
     this.invoice = invoice;
     this.changeDetector.detectChanges();
 });