ngAfterViewInit() {
   this._portal = new TemplatePortal(this._dialogTemplate, this._viewContainerRef);
   this._overlayRef = this._overlay.create({
     positionStrategy: this._overlay.position().global().centerHorizontally().centerVertically(),
     hasBackdrop: true
   });
   this._overlayRef.backdropClick().subscribe(() => this._overlayRef.detach());
 }

 // Create component to ApplicationRef
 private createModal(): void {
   this.overlayRef = this.overlay.create();
   this.modalRef = this.overlayRef.attach(new ComponentPortal(NzModalComponent));
 }

 destroyModal(): void {
   if (this.modalRef) {
     this.overlayRef.dispose();
     this.modalRef = null;
   }
 }

 close() {
   this.overlayRef.dispose();
 }

 close(): void {
     this.overlayRef.dispose();
 }

 openDialog() {
   this._overlayRef.attach(this._portal);
 }

 ngOnDestroy() {
   this._overlayRef.dispose();
 }