如何在“select”控件中动态设置默认值

我订阅 HTTP 服务器以接收数据，之后我的select控件将通过 Angular 框架加载数据。我的目标是设置默认值。我的默认值由我从服务器收到的对象的三个值组成，并用“/”分隔，因此 HTML 代码如下所示：

<label>{{ functionStr }}</label>
<select #element formControlName="selectedUser" class="form-select" (change)="changeClient($event)">
    <option *ngFor="let account of accountsAvailable4Function">{{ account.firstName }}/{{ account.lastName }}/{{ account.email }}
    </option>
</select>

我在初始化时使用了默认值FormGroup：

var selected = this.accountsAvailable4Function[1].firstName+"/"+this.accountsAvailable4Function[1].lastName+"/"+this.accountsAvailable4Function[1].email
this.form = this.formBuilder.group({
      scheduledDate: ['', Validators.required],
      selectedUser: [selected, [Validators.required]],
    });

这会引发异常，因为我的accountsAvailable4Function数组尚未初始化。

我尝试使用FormGroup如下控件来设置它。这也不起作用，因为我怀疑该控件尚未加载：

var selected = this.accountsAvailable4Function[1].firstName+"/"+this.accountsAvailable4Function[1].lastName+"/"+this.accountsAvailable4Function[1].email
this.f['selectedUser'].setValue(selected);
      

是否有一些我可以监听的事件，以便在加载选择控件时通知我？

附加：加载accountsAvailable4Function数组：

this.accountService.getAll()
      .pipe(first())
      .subscribe({
        next: (accounts: Account[]) => {
          accounts.forEach(account => {
            account.userFunctions.forEach(userFunc => {
              if(userFunc.userFunction == this.functionStr) {
                this.accountsAvailable4Function.push(account);
              }
            });
          });
          
          /* HTML select control selects by default first element - verify it*/
          this.selectedAccount = this.accountsAvailable4Function[0];
          this.dataSource = new MatTableDataSource(this.accountsSelected4Function);
          this.dataSource.paginator = this.paginator;

        },
        complete: () => {
          this.accountsLoaded = true;
          var selected = this.accountsAvailable4Function[1].firstName+"/"+this.accountsAvailable4Function[1].lastName+"/"+this.accountsAvailable4Function[1].email
          this.f['selectedUser'].setValue(selected);
        },
        error: error => {
          this.alertService.error(error);
          this.accountsLoaded = true;
        }
      });