Ionic 3发布请求在Android设备中不起作用

Question

当我向网站服务发送发布请求时，它可以在浏览器上运行，但在Android移动设备上却显示错误，例如状态为0：URL为null 请帮我解决这个问题。

我的service.ts

Login.ts
import { HttpClient, HttpHeaders } from '@angular/common/http';
import { Http, Response, Headers } from '@angular/http';
import { Injectable } from '@angular/core';
import { Observable } from 'rxjs/Observable';
import 'rxjs/add/operator/catch';
import 'rxjs/add/operator/map';
import 'rxjs/add/observable/throw';
@Injectable()
export class RestProvider {
  constructor(public httpClient : HttpClient, public http: Http) {
	    console.log('Hello RestProvider Provider');
	}
  
  getlogindetails(credentials) {
		let apiUrl = 'http://example.com/data/service.php?Method=';
		
        let headers = new HttpHeaders();
        headers.append('Content-Type', 'application/json');	
        return this.http.post(apiUrl+'Login', JSON.stringify(credentials))
        .map((res: Response) => res.json());
      }
}

import { HttpModule } from '@angular/http';
import { HttpClientModule } from '@angular/common/http';

imports: [
   
    HttpClientModule,
    HttpModule
    IonicModule.forRoot(MyApp)
  ],
  
   providers: [
    RestProvider
  ]
  
  export class AppModule {}

Login.ts文件

 import { RestProvider } from '../../providers/rest/rest';
    import { HttpClient } from '@angular/common/http';
    constructor(public loadingCtrl: LoadingController, public navCtrl: NavController, public navParams: NavParams, public modalCtrl: ModalController, public toastCtrl: ToastController, public restProvider: RestProvider, private http: HttpClient, public menu: MenuController) {

      }
      verifylogin() {
         this.restProvider.getlogindetails(this.loginData).subscribe((result)=>{
         console.log("result:"+result);
          }, (err) => {
          //this.loading.dismiss();
          alert("err:"+err);
          this.presentToast(err);
        });
      }

以上代码在浏览器上有效，但在android设备上无效。请帮我解决这个问题。