javascript - 错误错误 : Uncaught (in promise): TypeError: Cannot set property 'devices' of undefined in ionic 4 Angular

Question

我有一个名为 MyDevicesPage 的类，它控制我试图操作 res 对象的页面，然后将其传递给 DataService 的 updateDevicesToServer 方法以进行进一步操作。代码编译正常，但在运行时会抛出错误 ERROR Error: Uncaught (in promise): TypeError: Cannot set property 'devices' of undefined

这是类和关联的接口(interface)

export class MydevicesPage implements OnInit {  

  devices : Array<deviceInterface>
  constructor(private deviceService : DeviceService,private route:  ActivatedRoute,private router: Router, private authenticationService : AuthenticationService) { }

  ngOnInit() {
    this.deviceService.getDevices().then((res : devicesInterface) => {
      if(res){        
        let data : ResUpdateDevices
        data.devices = res;
        this.devices = res.devices;        

        data.token = this.authenticationService.getToken();

        this.deviceService.updateDevicesToServer(data).subscribe(res => {
          console.log(res)
        },err=>{
          console.log(err)
        });
      } 
    })
  }

  goto_device(ssid : String, name : String){
    this.router.navigate(['members','device',ssid,name])
  }

}

ResUpdateInterface接口(interface)

export interface ResUpdateDevices{
    devices : devicesInterface
    token : string
}

DeviceInterface接口(interface)

export interface deviceInterface {
  ssid : String,
  name : String
}

DevicesInterface接口(interface)

export interface devicesInterface {
  devices : Array<deviceInterface>  
}

Console Logging res 给出了这个

{devices : [{ssid:"ssid", name :"name"}]}

Answer 1

您收到此错误是因为您在尝试分配 data.devices = res; 之前没有初始化您的 data 对象。我建议进行以下更新:

let data: ResUpdateDevices = {
    devices: res,
    token: this.authenticationService.getToken(),
};
this.devices = res.devices;