android - Ionic 2 - NavController canGoBack() 始终未定义 (Android)

Question

这是我的功能:

checkStack(){
    let canGoBack = this.navCtrl.canGoBack()
    console.log('canGoBack: ',canGoBack);

    if(canGoBack === true){
        console.log('Not RootPage.');
    } else {

        let alert = this.alertCtrl.create({
            title: 'Exit',
            message: 'sure?',
            buttons: [
                {
                    text: 'Yes',
                    role: 'cancel',
                    handler: () => {
                        console.log('Cancel clicked');
                    }
                },
                {
                    text: 'No',
                    handler: () => {
                        this.platform.exitApp();
                    }
                }
            ]
        });

        alert.present();
    }
}

我正在调用 IonViewDidLoad():

this.platform.registerBackButtonAction(this.checkStack);

但是如果我点击 BackButton 它会失败并显示消息:

“未捕获的类型错误:无法读取未定义的属性‘canGoBack’”

怎么了？

Answer 1

这是我的解决方案:

constructor(public platform: Platform, public app: App){
   initializeApp()
}

this.platform.registerBackButtonAction(() => {

            let activeNav = this.app.getActiveNav();

            if(activeNav.canGoBack()){

                // not Root

            } else {

                // is Root

        }

我是这样定义的:

initializeApp(){
   this.platform.ready().then(() => {...})
}

并调用构造函数。效果很好 ;-)