IOS8 使用CoreLocation获取地理位置请求不弹出的解决方法：
1.在Info.list文件下添加一个键为NSLocationWhenInUseUsageDescription，值为想要给用户看到的文本（也可以为空）
2.定义一个CLLocationManager后，使用[_locationManager requestWhenInUseAuthorization];请求用户允许获取地理位置
CoreLocation获取地理位置的三种方式：
1：蜂窝基站：Cell tower triangulation will always work if there is a signal but it’s not very precise.
2：Wi-Fi：Wi-Fi positioning works better but that is only available if there are known Wi-Fi routers nearby. This system uses a big database that contains the locations of wireless networking equipment.
3：GPS卫星定位：You get the best results from the GPS (Global Positioning System) but that attempts a satellite communication and is therefore the slowest of the three. It also won’t work very well indoors.
编写获取地理位置时应处理以下几种情况：
• Finds a location with the desired accuracy
• Finds a location that is not as accurate as you’d like and you don’t get any more accurate readings
• Doesn’t find a location at all
• Takes too long finding a location