数据绑定无法以反应形式在angular2-multiselect中使用

Question

我正在使用angular 7中的反应形式的angular2-multiselect下拉菜单。我有一个单击按钮，可在单击时添加更多下拉菜单，然后在单击保存按钮时保存该数据。除数据绑定无效外，其他一切工作正常。我可以保存数据，但是当我再次打开表单进行编辑时，下拉列表为空。

                <div class="col-sm-9">
                  <a href="JavaScript:void(0);" (click)="addAttribute()">Add Drop Down</a>
                </div>
        </div>```

       ``` <form class="form-horizontal" [formGroup]="addFeatureForm" (ngSubmit)="onSaveFeature()">
        <div class="row" formArrayName="attributes"
            *ngFor="let attribute of addFeatureForm.get('attributes').controls; let i = index;">
            <div class="col-sm-12 col-lg-3" [formGroupName]="i">
              <div class="form-group row">
                <label for="nname" class="col-sm-3 text-right control-label col-form-label">ValidationType</label>
                <div class="col-sm-9">
                  <angular2-multiselect [data]="validationTypeList" formControlName="validation" [(ngModel)]="attribute.selectedItems" 
                    [settings]="dropdownValidationSettings"></angular2-multiselect>
                </div>
              </div>
            </div>
        </div>
        </form>```

        ```public addFeatureForm = this._fb.group({
            id: '',
            name: ['', Validators.required],
            icon: ['', Validators.required],
            type: ['', Validators.required],
            pattern: ['', Validators.required],
            matchType: ['', Validators.required],
            parent: null,
            attributes: this._fb.array([])
          });```