尝试diff'[object Object]'时出错。只允许数组和迭代4次

Question

我有4个下拉菜单  -FromYear-  -FromMonth-  -ToYear-  -ToMonth- 当我从第一次和第三次下拉菜单中选择一年时，它应该会有几个月的时间来填充我的其他下拉列表。  我使用selectFromYearsEvent

获得所选年份ID的月份

这是我的组件

export class CalendarComponent implements OnInit {

  year: number[];

  selectYears: Year[];

  selectedFromYear: Year;
  selectedToYear: Year;

  selectFromMonths: Month[];
  selectToMonths: Month[];

  selectedFromMonth: Month;
  selectedToMonth: Month;

  selectedMonths: Month[];

  months: Month[];

  constructor(private calendarService: CalendarService, private monthsService: MonthsService) {

  }

  ngOnInit() {
        this.getYears();
      }

  getYears() {
    this.calendarService.getYears().subscribe(y => {
      this.selectYears = y;
    });
  }

  getMonth() {
    this.calendarService.getYear(this.selectedFromYear.id).subscribe(y => {
      this.selectedFromYear.months = y;
      this.selectFromMonths = y;
    });
  }

  selectFromYearsEvent(newYear) {
    this.selectedFromYear = newYear;
    this.getMonth();

  }
}

这是我的HTML代码

<div class="container-calendar">
        <div class="calendar-dates">
        <!-- from part -->
        <div class="from-date">
          <div class="from-date-dropdown">
            <select name="fromYear" [(ngModel)]="selectYears" (ngModelChange)="selectFromYearsEvent($event)">      <!-- [(ngModel)]="selectedFromYear"> -->
              <option name="fromYear2" *ngFor="let year of selectYears" [ngValue]="year">                   
                  {{year.number}}
              </option>
            </select>
          </div>
        </div>
        <div class="from-date">
          <div class="state-dropdown">
            <select name="fromMonth" [(ngModel)]="selectFromMonths" (ngModelChange)="selectFromMonthEvent($event)"> <!-- [(ngModel)]="selectedFromMonth"> -->
              <option *ngFor='let month of selectFromMonth' [ngValue]="month"> 
                  {{month.name}}
              </option>
            </select>
          </div>
        </div>