问调用函数Angular 9后，值不会赋值给数组

EN

export class OrderExceptionReportComponent implements OnInit {

  public sessionData: ExceptionReportSessionData[] = [];
  newData: any;
  reports = [];

  constructor(private orderExceptionReportService: OrderExceptionReportService) {
  }

  public async getExceptionReportSessionData(): Promise<void> {
    return this.orderExceptionReportService.GetExceptionReportSessionData()
      .then(
        data => {
          this.sessionData = data;
        });   
  }  


  async ngOnInit() {
    await this.getExceptionReportSessionData();

  }

  sessionDataChange(evt) {
    const value = evt.target.value;
    console.log(`session index: ${value}`);
    console.log(this.sessionData);
    if (isNaN(Number(value))) {
      this.reports = [];
    } else {
      this.reports = this.sessionData[Number(value)].ReportFiles;
    }
    console.log(this.reports);
  }


}