在硬件后退按钮上检查是否存在任何模态，然后取消模态

Question

Ionic v4-在硬件后退按钮上，我必须检查是否存在任何模态。如果存在任何模态，则关闭该模态。如果没有模态，则返回上一页

我在下面的代码行中使用了

代码：

    private backButtonEvent() {
    this.platform.backButton.subscribe(async () => {
        debugger;
        try {
            let activeModal = await this.modalCtrl.getTop();
            debugger;
            if(activeModal) {
                activeModal.dismiss();
                return;
            }
        } catch(ex) { console.log(ex); }
        this.routerOutlet.forEach((ro: IonRouterOutlet) => {
            if (this.router.url === '/login' || this.router.url === '/home') {
                if (this.router.url === '/home') {
                    this.common.confirmShow('Exit', 'Do you want to exit the app ?\r\nYou will be logged out after closing the app').then(d => {
                        if (d == 1) {
                            navigator['app'].exitApp();
                        }
                    }).catch(e => { console.log(e); });    
                } else if (this.router.url === '/login') {
                    navigator['app'].exitApp();
                }
            }
            else if (ro && ro.canGoBack()) {
                ro.pop();
            }
        });
    });        
}

这里，它始终满足activeModal true