android - 无法读取未定义的属性 'latitude'

Question

我正在试用 ionic native。获取权限成功，但之后报错cannot read property 'latitude' of undefined。

注意* 我使用的是 android 模拟器，而不是物理设备。

    import { Component } from '@angular/core';
    import { Platform } from 'ionic-angular';
    import { Geolocation } from '@ionic-native/geolocation';
    import { AndroidPermissions } from '@ionic-native/android-permissions';

    export class GeolocationPage {

        latitude: number;
        longitude: number;

        constructor(private platform: Platform, private geolocation: Geolocation, private androidPermissions: AndroidPermissions) {

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

                this.androidPermissions.requestPermissions([this.androidPermissions.PERMISSION.ACCESS_COARSE_LOCATION]).then(
                    sucess => this.onSucess(),
                    err => this.onFailure()
                );

            });
        }

        onSucess(){
            alert('onSucess');

            this.geolocation.watchPosition().subscribe(pos => {
                this.latitude =  pos.coords.latitude;
                this.longitude = pos.coords.longitude;
            });
        }

        onFailure(){
            alert('onFailure');
        }
    }

Answer 1

 onSucess(){
     alert('onSucess');
     let _me = this
     this.geolocation.watchPosition().subscribe(pos => {
                 _me.latitude =  pos.coords.latitude;
                 _me.longitude = pos.coords.longitude;
             });
         }