从Observable数组填充时，Angular 2 md-select不绑定选定的值

Question

我有angular2反应形式，其中包含md-select以使用户从firebase中选择医生md-select在渲染组件之前数据存在时工作正常，但如果数据像asservable一样异步，则不显示选定值

 doctors$:Observable< Doctor[] > = this.doctorService.findAllDoctors();
 

  constructor(private fb:FormBuilder , public doctorService : DoctorService 
  ,private cdr: ChangeDetectorRef )

  {    
   
 this.doctors$= this.doctorService.findAllDoctors();
  
this.form = this.fb.group({
      FullName: ['',Validators.required],
      Ext: [''],
      BirthDate: ['',Validators.required],
      Gender: ['',Validators.required],
      Phone: ['',[Validators.required]],
      doctorId: ['']

    }); 
 

<md-select formControlName="doctorId" ngControl="doctorId"  placeholder="Doctor"  >
      <md-option *ngFor="let p of doctors$ | async  " [value]="p.value">{{p.value}}</md-option>

    </md-select>

在这里输入代码

Answer 1

解决方法在异步加载选项数据后用选定的值更新md-select

 ngOnInit() {
   
this.doctors$.subscribe(c=>{

    this.form.controls['doctorId'].patchValue(this.initialValue.doctorId);


});