ionic2APP 如何处理返回键问题

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1、APP中难免会有自定义各种modal、alert，modal或alert处于激活状态时android用户按物理返回键，页面被返回，而这些弹窗切没有被返回，一种解决办法是可以在每个组件内用生命周期钩子ionViewWillLeave监听有modal或是alert的页面，如果处于激活状态则先关闭它，当然这种状态简单却不高效；

2、封装一个服务，代码如下

import {Injectable} from '@angular/core';
import {Subject}    from 'rxjs/Subject';
import {TranslateService} from 'ng2-translate';

@Injectable()
export class ToastService {
  comfirmSubject = new Subject();

  // comfirmObservable$ = this.comfirmSubject.asObservable();
  _isActive = false;
  gobackWhenClose = false;
  model = null;
  is_access_modal:boolean = false;

  set isActive(active: boolean) {
    if(active) {
      this._isActive = true;
    } else {
      this._isActive = false;
      if(this.model) {
        this.model.dismiss();
        this.model = null;
      }
    }

  }

  get isActive() {
    return this._isActive || this.model;
  }

  constructor(private translate: TranslateService) {}

  // 普通弹框
  confirm(params: any) {
    this.comfirmSubject.next(params);
    this.isActive = true;
  }

  // 业务成功后弹框，title带成功的icon
  successConfirm(params: any) {
    params = Object.assign(params, {
      title: `<i class="icon-icons icon-icons-success"></i><span>${params['title'] || this.translate.get('TIPS.WENXINTISHI')['value']}</span>`
    });
    this.comfirmSubject.next(params);
    this.isActive = true;
  }

  // 业务失败后弹框
  errorConfirm(params: any) {
    params = Object.assign(params, {
      title: `<i class="icon-icons icon-icons-error"></i><span>${params['title'] || this.translate.get('TIPS.WENXINTISHI')['value']}</span>`
    });

    // 错误提示处理
    let feedbacks = this.translate.get('FEEDBACK')['value'];

    let content = params['body'];
    if (content) {
      if (content.indexOf('MSG.CLINETFUNDNOTENOUGH') > -1) {  //购买基金余额不足时，后台返回数据做了拆分
        params['body'] = feedbacks['MSG.CLIENTFUNDNOTENOUGH'] + '<span class="red">'+ content.split('|')[1] + '</span>'
      } else {
        params['body'] = feedbacks[content] || content;
      }
    }

    this.comfirmSubject.next(params);
    this.isActive = true;
  }
}

然后在APP.component.ts中去监听Android物理返回键，

}
if ( this.toastService.isActive && !this.toastService.is_access_modal) { // 当前有自定义toast，关闭toast
  this.toastService.isActive = false;  //包括toast和model
  if(this.toastService.gobackWhenClose) {
    this.toastService.gobackWhenClose = false;
    this.toastService._isActive = false;
    this.events.publish('backto');
  }
  return;
}

其中有多余的代码（为了符合自己业务需求，主要是isActive这个变量及