Ionic4--android物理返回按鈕無效

問題：安卓的物理返回按鈕有時有效果有時沒效果

方法：可能是獲取設備類型的方法是異步的，沒有正確返回設備號。

下面是代碼：

import { NavController, ActionSheetController, AlertController, MenuController, ModalController, PopoverController, Platform } from '@ionic/angular';

constructor(public navController: NavController,
    public eventService: EventService,
    public alertCtrl: AlertController,
    public modalCtrl: ModalController,
    public menuCtrl: MenuController,
    public actionSheetCtrl: ActionSheetController,
    public popoverCtrl: PopoverController,
    public platform: Platform) { }


ngOnInit(): void {
    this.androidBackButtonAction();
}

androidBackButtonAction() {
    this.platform.ready().then(() => {//獲取設備異步
      if (this.tool.devicePlatformType() == 2) {
        this.platform.backButton.subscribe(() => {
          this.tabsCanGoBack = this.tabs.outlet.canGoBack();
          this.tabsParentCanGoBack = this.tabs.outlet.parentOutlet.canGoBack();
          this.androidBackButtonHandle();
        });
      }
    })
}

async androidBackButtonHandle() {
    try {
      const alert = await this.alertCtrl.getTop();
      if (alert) {
        alert.dismiss();
        return;
      }
      const action = await this.actionSheetCtrl.getTop();
      if (action) {
        action.dismiss();
        return;
      }
      const popover = await this.popoverCtrl.getTop();
      if (popover) {
        popover.dismiss();
        return;
      }
      const modal = await this.modalCtrl.getTop();
      if (modal) {
        modal.dismiss();
        return;
      }
      const isOpen = await this.menuCtrl.isOpen();
      if (isOpen) {
        this.menuCtrl.close();
        return;
      }
      if (!this.tabsCanGoBack && !this.tabsParentCanGoBack) {
        this.tool.appMinimize();
        return;
      }
    } catch (error) {
    }
  }