@ViewChild('mainTabs') tabs:Tabs;//声明tabs组件()

@ViewChild('myNav') nav: Nav;//声明根组件()

platform.ready().then(()=>{
this.exitApp();
})
public backButtonPressed: boolean = false;
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 LoginPage) {//查看当前页面是否是登陆页面
    this.showExit();
    return;
   }
   this.appCtrl.getActiveNav().pop();//剩余的情况全部使用全局路由进行操作 
  });
 }
 
 //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();
 }