ionic3双击返回退出应用的方法

import {Component, ViewChild} from '@angular/core';
 
import { AboutPage } from '../about/about';
import { ContactPage } from '../contact/contact';
import { HomePage } from '../home/home';
import { MyPage } from '../my/my';
import {Tabs} from "ionic-angular";
 
@Component({
 templateUrl: 'tabs.html'
})
export class TabsPage {
 tab1Root = HomePage;
 tab2Root = AboutPage;
 tab3Root = ContactPage;
 tab4Root = MyPage;
 @ViewChild('mainTabs') tabs:Tabs;
 constructor() {
 
 }
}

<ion-tabs #mainTabs>
 <ion-tab [root]="tab1Root" tabTitle="定位" tabIcon="ios-pin-outline" ></ion-tab>
 <ion-tab [root]="tab2Root" tabTitle="运输管理" tabIcon="ios-paper-outline"></ion-tab>
 <ion-tab [root]="tab3Root" tabTitle="账单管理" tabIcon="logo-yen"></ion-tab>
 <ion-tab [root]="tab4Root" tabTitle="我的" tabIcon="ios-contact-outline"></ion-tab>
</ion-tabs>

import {Component, ViewChild} from '@angular/core';
import {Nav, Platform, ToastController,App} from 'ionic-angular';
import { StatusBar } from '@ionic-native/status-bar';
import { SplashScreen } from '@ionic-native/splash-screen';
import { Login } from '../pages/login/login';
import { TabsPage } from '../pages/tabs/tabs';
 
@Component({
 templateUrl: 'app.html'
})
export class MyApp {
 rootPage:any;
 public backButtonPressed: boolean = false;
 @ViewChild("myNav") nav: Nav;
 constructor(public platform: Platform,statusBar: StatusBar, splashScreen: SplashScreen,
       public toastCtrl: ToastController,public appCtrl:App) {
  platform.ready().then(() => {
   this.exitApp();
  });
 }
 
 exitApp() {
  this.platform.registerBackButtonAction(() => {
   //控制modal、系统自带提示框
   let overlay = this.appCtrl._appRoot._overlayPortal.getActive() ||  this.appCtrl._appRoot._modalPortal.getActive();
   if (overlay) {
    overlay.dismiss();
    return;
   }
   let activeVC = this.nav.getActive();
   let page = activeVC.instance;
   if (page.tabs) {
    let activeNav = page.tabs.getSelected();
    if (activeNav.canGoBack()) {
     return activeNav.pop();
    } else {
     return this.showExit();
    }
   }
   if (page instanceof Login) {//查看当前页面是否是登陆页面
    this.showExit();
    return;
   }
   this.appCtrl.getRootNav().pop();//剩余的情况返回操作
  });
 }
 
 //双击退出函数
 showExit() {
  if (this.backButtonPressed) {
   this.platform.exitApp();
  } else {
   this.presentToast();//再按一次退出
   this.backButtonPressed = true;
   setTimeout(() => {
    this.backButtonPressed = false;
   }, 2000)
  }
 }
 presentToast() {
  let toast = this.toastCtrl.create({
   message: '再按一次退出应用',
   duration: 2000,
   position: 'top',
  });
  toast.onDidDismiss(() => {
   console.log('Dismissed toast');
  });
  toast.present();
 }
}

<ion-nav #myNav [root]="rootPage"></ion-nav>