Angular4 : select [selected] not work for the first time

Question

有一个代码:

<select name="department" class="form-control select" [(ngModel)]="departments" formControlName="departmentControl">    
    <option *ngFor="let department of departments" [ngValue]="department" [selected]="department.id == this.departmentid">
      {{ department.name }}
    </option>
  </select>

和功能:

isSelected(department): boolean {
  debugger;
  return department.id == this.departmentid;
}

部门 - 是用户详细信息组件的嵌套组件。第一次选择用户详细信息组件后，未选择部门。但是第二次一切正常。哪里出错了？

Answer 1

不需要:[selected]="department.id == this.departmentid"，因为您正在使用 [(ngModel)]
将 [(ngModel)]="departments" 更改为 [(ngModel)]="departmentid"
将 [ngValue]="department" 更改为 [ngValue]="department.id"
最后它应该是这样的:

<select name="department" class="form-control select" [(ngModel)]="departmentid" formControlName="departmentControl">    
    <option *ngFor="let department of departments" [ngValue]="department.id" >
        {{ department.name }}
    </option>
</select>

WORKING DEMO