ionic2如何处理android硬件返回按钮

 import {Component, ViewChild} from '@angular/core'; import {Platform, ToastController, Nav, IonicApp} from 'ionic-angular'; import {StatusBar, Splashscreen} from 'ionic-native'; import {TabsPage} from '../pages/tabs/tabs'; @Component({  templateUrl: 'app.html' }) export class MyApp {  rootPage = TabsPage;  backButtonPressed: boolean = false; //用于判断返回键是否触发  @ViewChild('myNav') nav: Nav;  constructor(public ionicApp: IonicApp, public platform: Platform, public toastCtrl: ToastController) {   platform.ready().then(() => {    StatusBar.styleDefault();    Splashscreen.hide();    this.registerBackButtonAction();//注册返回按键事件   });  }  registerBackButtonAction() {   this.platform.registerBackButtonAction(() => {    //如果想点击返回按钮隐藏toast或loading或Overlay就把下面加上    // this.ionicApp._toastPortal.getActive() || this.ionicApp._loadingPortal.getActive() || this.ionicApp._overlayPortal.getActive()    let activePortal = this.ionicApp._modalPortal.getActive();    if (activePortal) {     activePortal.dismiss().catch(() => {});     activePortal.onDidDismiss(() => {});     return;    }    let activeVC = this.nav.getActive();    let tabs = activeVC.instance.tabs;    let activeNav = tabs.getSelected();    return activeNav.canGoBack() ? activeNav.pop() : this.showExit();//另外两种方法在这里将this.showExit()改为其他两种的方法的逻辑就好。   }, 1);  }  //双击退出提示框  showExit() {   if (this.backButtonPressed) { //当触发标志为true时，即2秒内双击返回按键则退出APP    this.platform.exitApp();   } else {    this.toastCtrl.create({     message: '再按一次退出应用',     duration: 2000,     position: 'top'    }).present();    this.backButtonPressed = true;    setTimeout(() => this.backButtonPressed = false, 2000);//2秒内没有再次点击返回则将触发标志标记为false   }  }}

 <ion-tabs #mainTabs>  <ion-tab [root]="tab1Root" tabTitle="Home" tabIcon="home"></ion-tab>  <ion-tab [root]="tab2Root" tabTitle="About" tabIcon="information-circle"></ion-tab>  <ion-tab [root]="tab3Root" tabTitle="Contact" tabIcon="contacts"></ion-tab> </ion-tabs>

 import {Component, ViewChild} from '@angular/core'; import { HomePage } from '../home/home'; import { AboutPage } from '../about/about'; import { ContactPage } from '../contact/contact'; import {Tabs} from "ionic-angular"; @Component({  templateUrl: 'tabs.html' }) export class TabsPage {  @ViewChild('mainTabs') tabs:Tabs;//加这句以及引用两个模块  tab1Root: any = HomePage;  tab2Root: any = AboutPage;  tab3Root: any = ContactPage;  constructor() {  } }