the NbDialogService doesn't open when i trie to open it in ngOnInit methode

import { Component, OnInit } from "@angular/core";
import { ModalService } from "../../services/modal.service";
import { NbDialogService, NbWindowService } from "@nebular/theme";
import { VersionModalComponent } from "../modal/version-modal/version-modal.component";

@Component({
selector: "ngx-dashboard",
templateUrl: "./dashboard.component.html"
})
export class DashboardComponent implements OnInit {
constructor(
private modalService: ModalService,
private dialogService: NbDialogService,
private windowService: NbWindowService
) {}

ngOnInit() {
this.dialogService.open(VersionModalComponent, {});
}

}