Angular 为什么在subscribe未定义后从服务获取数据？

我定义了一个接口

export interface IEmployee
{
    maNV?:number,
    hoTen?:string,
    gioiTinh?:string,
    ngaySinh?:Date,
    diaChi?:string,
    cmnd?:string,
    sdt?:string,
    luong?:number,
    ngayBatDauLam?:Date,
    maNguoiQuanLy?:number,
    isDelete?:boolean
}

我创建了一个文件

employee.json

包含一些员工的信息：

[
    {"maNV":1,"hoTen":"nguyen quang du","gioiTinh":"nam","ngaySinh":"03/02/1999","diaChi":"Hà Tây","cmnd":"1131131231231232","sdt":3123123141,"luong":300,"ngayBatDauLam":"03/01/2020","maNguoiQuanLy":1,"isDelete":false},
    {"maNV":2,"hoTen":"nguyen thi duyen","gioiTinh":"nu","ngaySinh":"03/02/1999","diaChi":"Hà Tây","cmnd":"1131131231231232","sdt":3123123141,"luong":300,"ngayBatDauLam":"03/01/2020","maNguoiQuanLy":1,"isDelete":false},
    {"maNV":3,"hoTen":"khuat quang chien","gioiTinh":"nam","ngaySinh":"03/02/1999","diaChi":"Hà Tây","cmnd":"1131131231231232","sdt":3123123141,"luong":300,"ngayBatDauLam":"03/01/2020","maNguoiQuanLy":1,"isDelete":false}


]

然后我创建一个服务，从

employee.json

import { Injectable } from '@angular/core';
import {HttpClient} from '@angular/common/http'
import {IEmployee} from './employee/employee'
import {Observable} from 'rxjs'
@Injectable({
  providedIn: 'root'
})
export class EmployeeService {
  private _url:string="../assets/data/employees.json";
  constructor(private http:HttpClient) {}
  getEmployees():Observable<IEmployee[]>
  {
    return this.http.get<IEmployee[]>(this._url);
  }
}

---

我发现

这个。数据
是
未定义的
。我不知道为什么我定义它是
数组
。并帮助我将其转换为
数组
类型，这是因为您在httpClient获取数据之前记录了数据，请记住httpClient.get是一种异步方法，如果需要，可以将console.log移动到订阅中，并且它应该可以正常工作：

ngOnInit():void
{
    this.service.getEmployees().subscribe(data=>{
      this.data=data; 
      console.log(this.data);
    }) ;

}

这是因为您是在httpClient获取数据之前记录数据的，请记住httpClient.get是一个异步方法，如果您希望将console.log移动到订阅中，它应该可以正常工作：

ngOnInit():void
{
    this.service.getEmployees().subscribe(data=>{
      this.data=data; 
      console.log(this.data);
    }) ;

}