问Show hidden mat-当所有其他内容被过滤掉时的选项

EN

<div class="col-md-6">
    <form *ngIf="preferencesFormGroup" [formGroup]="preferencesFormGroup">
      <mat-form-field *ngFor="let tagType of tagTypes$ | async">
        <mat-select placeholder="{{tagType.name}}" multiple #select [formControlName]="tagType.name">
          <mat-select-trigger>
            <mat-chip-list>
              <mat-chip *ngFor="let tag of preferencesFormGroup.controls[tagType.name].value" [removable]="true"
                (removed)="onTagsRemoved(tagType.name, tag)">
                {{ tag }}
                <mat-icon matChipRemove>cancel</mat-icon>
              </mat-chip>
            </mat-chip-list>
          </mat-select-trigger>
          <div class="search-wrapper">
            <input matInput placeholder="Search tags" [formControlName]="tagType.name + 'Search'" type="text"
              id="searchInput">
            <a mat-icon-button id="resetButton" (click)="clearFilter(tagType.name)">
              <mat-icon aria-label="Icon-button for clearing the input" id="clearIcon" [inline]="true">clear</mat-icon>
            </a>
          </div>
          <hr id="hrSearch">
          <mat-option
          *ngFor="let tag of tagType.tags | contains : preferencesFormGroup.controls[tagType.name+'Search'].value"
          [value]="tag.name">{{tag.name}}</mat-option>
          <mat-option *ngIf="noMoreOptions" (click)="createNewTag(tagType.name)"><i>Didn't find the tag you want? Click here to create your own.</i></mat-option>
        </mat-select>
      </mat-form-field>
    </form>
    <div class="row" style="align-items: center;">
      <div class="col-md-6">
        <div class="row" *ngIf="addDropDownActive" style="align-items: center;">
          <div class="col-md-8">
            <mat-form-field>
              <input matInput placeholder="Add new preference" type="text" [(ngModel)]="newPreference">
            </mat-form-field>
          </div>
          <div class="col-md-4">
            <button mat-button mat-stroked-button color="accent" (click)="createDropdown()"
              [disabled]="(newPreference === null) || (newPreference === '')">Save</button>
          </div>
        </div>
      </div>
      <div class="col-md-6">
        <button mat-button (click)="switchVisible()" color="accent" class="float-right">{{preferenceBtn}}</button>
      </div>
    </div>

    <div class="row mt-3">
      <div class="col-md-6">
        <button mat-button mat-stroked-button class="float-left" color="accent"
          (click)="goToPreviousStep()">Back</button>
      </div>
      <div class="col-md-6">
        <button mat-button mat-raised-button class="float-right" color="accent" (click)="goToNextStep()">Next</button>
      </div>
    </div>
  </div>

@Component({
  selector: 'tours-tour-tag',
  templateUrl: './tour-tag.component.html',
  styleUrls: ['./tour-tag.component.css']
})
export class TourTagComponent implements OnInit {

  tagTypes$: Observable<TagType[]>;
  preferencesFormGroup: FormGroup;
  addDropDownActive = false;
  newPreference: string = null;
  preferenceBtn = 'Create new preference';
  filterPropertySearch = '';
  noMoreOptions = false;

  @ViewChild('select') matSelect: MatSelect;

  constructor(private store: Store) { }

  ngOnInit(): void {
    this.tagTypes$ = this.store.select(TagTypeSelectors.selectAllTagTypes);
    this.tagTypes$.subscribe((tagTypes) => { this.initForm(tagTypes) });
  }

  onTagsRemoved(tagTypeName: string, tag: string) {
    const tags = this.preferencesFormGroup.controls[tagTypeName].value as string[];
    this.removeFirst(tags, tag);
    this.preferencesFormGroup.controls[tagTypeName].setValue(tags);
  }

  private removeFirst<T>(array: T[], toRemove: T): void {
    const index = array.indexOf(toRemove);
    if (index !== -1) {
      array.splice(index, 1);
    }
  }

  switchVisible() {
    this.addDropDownActive = !this.addDropDownActive;
    if (this.addDropDownActive) {
      this.preferenceBtn = 'Close';
    } else {
      this.preferenceBtn = 'Create new preference';
    }
    this.newPreference = null;
  }

  initForm(tagTypes: TagType[]) {
    this.preferencesFormGroup = new FormGroup({});
    tagTypes.forEach((tagType: TagType) => {
      this.preferencesFormGroup.addControl(tagType.name, new FormControl([]));
      const searchFormControl = new FormControl([]);
      searchFormControl.setValue('');
      this.preferencesFormGroup.addControl(tagType.name + 'Search', searchFormControl);
    });
    console.log(this.preferencesFormGroup);
  }

  createDropdown() {
    const newTagType: TagType = { id: null, code: null, name: this.newPreference, tags: null };
    this.store.dispatch(TagTypeActions.createTagType({ tagType: newTagType }));
    this.switchVisible();
  }

  clearFilter(tagTypeName: string): void {
    const searchControlName = tagTypeName.concat('Search');
    this.preferencesFormGroup.controls[searchControlName].setValue('');
  }

  createNewTag(tagTypeName: string) {
    console.log('open modal component');
  }
}