1.安装插件 http; ionic4 项目目录下先运行

ionic cordova plugin add cordova-plugin-advanced-http

后运行

npm install @ionic-native/http

在./src/app/app.module.ts中增加(...和...中间的内容，两处)

...
import { HTTP } from '@ionic-native/http/ngx';
...

@NgModule({
  declarations: [AppComponent],
  entryComponents: [],
  imports: [BrowserModule, IonicModule.forRoot(), AppRoutingModule],
  providers: [
  ...
    HTTP,
  ...
    { provide: RouteReuseStrategy, useClass: IonicRouteStrategy }
  ],
  bootstrap: [AppComponent]
})
export class AppModule {}

toast插件同上 命令代码为

ionic cordova plugin add cordova-plugin-x-toast
npm install @ionic-native/toast
import { ToastController } from '@ionic/angular';//这个是代码

新建service文件

ionic g service <目录/文件名>
ionic g service ./providers/commonService //这是我的命令

common.service.ts文件内增加

...
import { HTTP } from '@ionic-native/http/ngx';
import { LoadingController } from '@ionic/angular';//整个是进度遮罩层
import { ToastController } from '@ionic/angular';
...

export class CommonService {

  constructor(
    ...
    private toastCtrl: ToastController,
    private http: HTTP,
    private loadingController: LoadingController, 
    ...
  ) {

  }

...
 /**
     * 显示toast
     * @param data  要显示的内容
     * @param time  显示时间 默认2000毫秒
    */
  public async TOAST(data: string, time?: number) {

    if (typeof (time) == "undefined") {
      time = 2000;
    }

    let toast = await this.toastCtrl.create({
      message: data,
      duration: time,
      position: "middle"
    });
    toast.present();
  }

private async POST(serverUrl: string, uploadData?: any, headers?: any) {
    let temParam: any;

    if (typeof uploadData === 'object') {
      temParam = uploadData;
    } else {
      temParam = {
        json: uploadData,
      };
    }

    const loading = await this.loadingController.create({
      message: '请稍后...',
    });

    await loading.present();

    var promise = this.http.post(serverUrl, temParam, headers);

    promise.then(data => {
      loading.dismiss();

      let tmp = JSON.parse(data.data);

      if (tmp.msg) {
        if (tmp.msg == '证书无效') {
          this.TOAST('账户在其他设备登录,请重试');
          DataService.accessToken = null;
          localStorage.removeItem('accessToken');
          this.router.navigateByUrl('/login');
        }
      }
    }).catch(error => {
      loading.dismiss();
      this.TOAST("网络出错,请检查网络");

    });

    return promise;
  }

 /**
  * 业务网络请求
  * @param business 业务名称
  * @param param 需要携带的参数,可为空
  * @param loadingFlag 为空时显示进度条遮罩层,不为空不显示
  */
  public SEND(business: string, param?: any, loadingFlag?: any, headers?: any) {

    if (param) {
      param.access_token = DataService.accessToken;
    } else {
      param = { access_token: DataService.accessToken };
    }

    if (loadingFlag) {
      return this.NO_LOADING_POST(business, param, headers);
    } else {
      return this.POST(business, param, headers);
    }

  }

  private async NO_LOADING_POST(serverUrl: string, uploadData?: any, headers?: any) {
    let temParam: any;

    if (typeof uploadData === 'object') {
      temParam = uploadData;
    } else {
      temParam = {
        json: uploadData,
      };
    }

    var promise = this.http.post(serverUrl, temParam, headers);

    promise.catch(error => {
      this.TOAST("网络出错,请检查网络");
    });

    return promise;
  }
...
}

调用方式
在相应ts文件中

...
import { CommonService } from '../../providers/common.service';
...

  constructor(
    ...
    private service: CommonService,
    ...
  ) { }

...
let body = {

      
        WAGE: this.WAGE,//工资
        AGENT: this.AGENT,//经办人

        EMP_STATUS: this.EMP_STATUS,//人员状态
        RRC: this.RRC,//户口性质
        P_STATUS: this.P_STATUS,//个人身份
        P_M_STATUS: this.P_M_STATUS,//医疗人员类别
        ALTID: this.ALTID//ALTID
      }

      this.service.SEND(DataService.uplodaAddress, body).then(data => {

        let tmp = JSON.parse(data.data);

        //do what you want
      });
...