在 angular 中成功调用订阅后未定义

Question

我已经成功调用了 API 并从中调用了数据，但是如果我读取了变量，我会得到"Undefined"。

调用api获取数据的服务类

export class DataServiceService {

   constructor(private http: Http) { }

   url: string = "http://localhost:60263/api/values";

   getEmployeesData(): Observable<EmployeeDetails[]> {
      return this.http.get(this.url).map((res: Response) => res.json());
   }
}

订阅数据

export class AppComponent {

   emp: EmployeeDetails[];

   constructor(private dataServe: DataServiceService) { }

   ngOnInit() {
     this.dataServe.getEmployeesData().subscribe(res => this.emp = res);
   }

   clEmployeesCount: Number = this.emp.length; **Getting undefined here**
   clShowEmployee: boolean = false;
   clCreateEmployee: boolean = false;
}

但是这在 HTML 部分工作正常

<div *ngIf="emp">
  <ul *ngFor="let user of emp">
   <li>{{user.ID}}</li>
 </ul>
</div>

Answer 1

由于它是一个异步调用，您无法知道它何时会被返回。所以将赋值移到subscribe函数中

this.dataServe.getEmployeesData().subscribe(res =>  {
   this.emp = res;
   this.clEmployeesCount = emp.length;
});