/**
  * Opens the projection dialog for the given projectable. After the user's choice,
  * the projectors will be updated.
  *
  * @param obj The projectable.
  */
 public async openProjectDialogFor(obj: Projectable | ProjectorElementBuildDeskriptor): Promise<void> {
     let descriptor: ProjectorElementBuildDeskriptor;
     if (isProjectable(obj)) {
         descriptor = obj.getSlide(this.configService);
     } else {
         descriptor = obj;
     }
     const dialogRef = this.dialog.open<
         ProjectionDialogComponent,
         ProjectorElementBuildDeskriptor,
         ProjectionDialogReturnType
     >(ProjectionDialogComponent, {
         maxHeight: '90vh',
         autoFocus: false,
         data: descriptor
     });
     const response = await dialogRef.afterClosed().toPromise();
     if (response) {
         const [action, projectors, projectorElement]: ProjectionDialogReturnType = response;
         if (action === 'project') {
             this.projectorService.projectOnMultiple(projectors, projectorElement);
         } else if (action === 'addToPreview') {
             projectors.forEach(projector => {
                 this.projectorService.addElementToPreview(projector, projectorElement);
             });
         }
     }
 }

 /**
  * Returns a view model associated with the identifiable projector element. Throws an error,
  * if the element is not mappable.
  *
  * @param element The projector element
  * @returns the view model from the projector element
  */
 public getViewModelFromProjectorElement<T extends BaseProjectableViewModel>(
     element: IdentifiableProjectorElement
 ): T {
     this.assertElementIsMappable(element);
     const viewModel = this.viewModelStore.get<T>(element.name, element.id);
     if (viewModel && !isProjectable(viewModel)) {
         console.error('The view model is not projectable', viewModel, element);
     }
     return viewModel;
 }

 /**
  * Retusn the identifiable projector element from the given types of slides/elements/descriptors
  *
  * @param obj Something related to IdentifiableProjectorElement
  * @returns the identifiable projector element from obj.
  */
 private getProjectorElement(
     obj: Projectable | ProjectorElementBuildDeskriptor | IdentifiableProjectorElement
 ): IdentifiableProjectorElement {
     if (isProjectable(obj)) {
         return obj.getSlide(this.configService).getBasicProjectorElement({});
     } else if (isProjectorElementBuildDeskriptor(obj)) {
         return obj.getBasicProjectorElement({});
     } else {
         return obj;
     }
 }