我正在使用 p-dropdown 显示国家列表并选择国家。所以我在 data.length 处收到错误，说运算符 '<' 不能应用于类型 'number' 和 'Observable'。我不知道如何解决这个错误。我是 angular 新手。请给出解决方案。

Countries:SelectItem[];


this.Countries.push({ label: 'Select Item', value: -1});

var data =  this.http.get('app/form/country.json')

for(let i = 0; i< data.length; i++) {

     this.Countries.push({label: data[i].Country, value: data[i].Name});
}

contact.component.ts

import { Component, OnInit } from '@angular/core';
import { SelectItem } from 'primeng/api';
import { CountryService } from './country-list.service';
import { StateService } from './state-list.service';
import { CityService } from './city-list.service';
import { Message } from 'primeng/components/common/api';
import { FormGroup, FormBuilder, FormControl, Validators } from '@angular/forms';
import { PersonListService,Address, Email, ContactNumber} from './person-list.service';
import { HttpClient } from '@angular/common/http';

@Component({ 
  moduleId: module.id,
  selector: 'sd-contactform',
  templateUrl: 'contactform.component.html',
  styleUrls: ['contactform.component.css']
})
export class ContactFormComponent implements OnInit {

  addresses: Address[];
  addresstype: Array<String>=[''];
  states:Array<String>=[''];
  countries:Array<String>=[''];
  errorMessage: any;
  Countries:SelectItem[];
  Country:string;
  emails:Email[];
  contactnumbers:ContactNumber[];     
  date3: Date;
  dates: Date[];
  rangeDates: Date[];
  minDate: Date;
  maxDate: Date;
  es: any;
  invalidDates: Array<Date>;
  val2: string = 'Male';
  val3: string = 'Unmarried';
  text: string;
  ValidIds: SelectItem[];
  selectedvalidid2: string = '';
  Religions: SelectItem[];
  selectedvalidid3: string = '';
  BloodGroups: SelectItem[];
  selectedvalidid4: string = '';
  AddressTypes: SelectItem[];
  selectedvalidid5: string = '';
  EmailTypes: SelectItem[];
  emailtype:Array<String>=[''];
  contacttype:Array<String>=[''];
  ContactTypes: SelectItem[];
  country: any;
  filteredCountriesSingle: any[];
  filteredStatesSingle: any[];
  city: any;
  filteredCitiesSingle: any[];
  msgs: Message[] = [];
  address: FormGroup;
  email: FormGroup;
  contact: FormGroup;
  submitted: boolean;
  i:number;
  data: any;


  constructor(public personListService:PersonListService,private countryService: CountryService,private http: HttpClient,private stateService: StateService,private cityService: CityService,private fb: FormBuilder) { }

  filterCountrySingle(event) {
      let query = event.query;
      this.countryService.getCountries().then(countries => {
          this.filteredCountriesSingle = this.filterCountry(query, countries);
      });
  }

  filterCountry(query, countries: any[]):any[] {

    let filtered : any[] = [];
    for(let i = 0; i < countries.length; i++) {
        let country = countries[i];
        if(country.country.toLowerCase().indexOf(query.toLowerCase()) == 0) {
            filtered.push(country);
        }
    }
    return filtered;
}

filterStateSingle(event) {
    let query = event.query;
    this.stateService.getStates().then(states => {
        this.filteredStatesSingle = this.filterState(query,states);
    });
}

filterState(query,states: any[]):any[] {

  let filtered : any[] = [];
  for(let i = 0; i < states.length; i++) {
      let state = states[i];
      if(state.state.toLowerCase().indexOf(query.toLowerCase()) == 0) {
          console.log(state)
          console.log(filtered)
          filtered.push(state);
      }
  }
  return filtered;
}

filterCitySingle(event) {
    let query = event.query; 
    this.cityService.getCitys().then(cities => {
        this.filteredCitiesSingle = this.filterCity(query,cities);
    });
}

filterCity(query,cities: any[]):any[] {

  let filtered : any[] = [];
  for(let i = 0; i < cities.length; i++) {
      let city = cities[i];
      if(city.city.toLowerCase().indexOf(query.toLowerCase()) == 0) {
        console.log(city);
        filtered.push(city);  
      }
  }
  return filtered;
}

  ngOnInit() {

    this.getperson();

    this.address = this.fb.group({
        'addresstype': new FormControl('', Validators.required),
        'addressl1': new FormControl('', Validators.required),
        'addressl2': new FormControl('', Validators.required),
        'state1': new FormControl('', Validators.required),
        'locality': new FormControl('', Validators.required),
        'city': new FormControl('', Validators.required),
        'country': new FormControl('', Validators.required),
        'postalcode': new FormControl('', Validators.required)  
    }
);

    this.email = this.fb.group({
        'emailtype': new FormControl('', Validators.required),
        'emailid': new FormControl('', [Validators.required,
        Validators.pattern("[a-z0-9._%+-]+@[a-z0-9.-]+\.[a-z]{2,3}$")] )
    }
);

    this.contact = this.fb.group({
        'contacttype': new FormControl('', Validators.required),
        'countrycode': new FormControl('', Validators.required),
        'regioncode': new FormControl('', Validators.required),
        'mobileno': new FormControl('', [Validators.required,Validators.minLength(10),Validators.maxLength(10)])
    }
);
    this.AddressTypes = [
      {label: 'Native', value: 'Native'},
      {label: 'Temporary', value: 'Temporary'},
      {label: 'Permanent', value: 'Permanent'},
      {label: 'Careof', value: 'Careof'}  
  ];

  this.EmailTypes = [
    {label: 'Personal', value: 'Personal'},
    {label: 'Office', value: 'Office'}  
];

    this.ContactTypes = [
        {label: 'Home', value: 'Home'},
        {label: 'Office', value: 'Office'}
];

var data = [];
this.Countries=[];
this.Countries.push({ label: 'Select Item', value: -1})

this.http.get('app/form/country.json')
  .subscribe(data => this.data = data, // success path
  error => this.errorMessage = error // error path
);
for(let i = 0; i<this.data.length ; i++) {
     //the property after data[i]. needs to match the exact name that is on your JSON file... So, name is a different property than Name
     this.Countries.push({label: this.data[i].country, value: this.data[i].Value});
     console.log(this.data[i].Value)
}

}

    onSubmit(value: string) {
        this.submitted = true;
        this.msgs = [];
        this.msgs.push({severity:'info', summary:'Success', detail:'Form Submitted'});
    }

    getperson(){
        this.personListService.getAddress()
         .subscribe(
          resp => {
          this.addresses = resp.Addresses
          var i;
          for(i=0;i<this.addresses.length;i++)
          {
            this.states[i]=this.addresses[i].State
            //this.countries[i]=this.addresses[i].Country
           this.addresstype[i]=this.addresses[i].AddressType
          }
          console.log(this.addresstype)
          console.log(this.states)
          console.log(this.countries)
          console.log(this.addresses)
          });

        this.personListService.getEmail()
         .subscribe(
          resp =>{
            this.emails = resp.Emails
            var i;
            for(i=0;i<this.emails.length;i++)
            {
             this.emailtype[i]=this.emails[i].EmailType
            }
          console.log(this.emails.length)
        }    
        );

         this.personListService.getContact()
         .subscribe(
          resp => {
          this.contactnumbers = resp.ContactNumbers
          var i;
          for(i=0;i<this.contactnumbers.length;i++)
          {

           this.contacttype[i]=this.contactnumbers[i].ContactType

        }
           //resp => this.addresses = resp.Addresses,
           error => this.errorMessage = <any>error
    }
         ); 
       }
    }

我添加了 compnent.ts 文件的代码。请检查，我收到错误为 ERROR TypeError: Cannot read property 'length' of undefined at data.length 所以请告诉我出了什么问题？