ionic3——app.component.ts中关闭modal

import {IonicApp} from 'ionic-angular';
constructor(
              private ionicApp: IonicApp
  ) {}
  let activeModal=this.ionicApp._modalPortal.getActive();
      if(activeModal){
        console.log("model is openning");
        activeModal.dismiss();
        return;
      }

可于双击返回退出app时，处理modal；