iOS上有两种消息通知，一种是本地消息（Local Notification），一种是远程消息(Push Notification，也叫Remote Notification)，设计这两种通知的目的都是为了提醒用户，现在有些什么新鲜的事情发生了，吸引用户重新打开应用。本地推送也可以通过服务器控制，比如说如果有新消息了，推送消息，但是，前提是程序必须是打开的，而远程推送，是通过苹果APNS服务器，推送给手机，手机在推送给具体的哪个程序，一般远程推送用到的比较多。
在iOS8之后，以前的本地推送写法可能会出错，接收不到推送的信息，
如果出现以下信息：
1 Attempting to schedule a local notification
2 with an alert but haven't received permission from the user to display alerts
3 with a sound but haven't received permission from the user to play sounds
说明在IOS8下没有注册，所以需要额外添加对IOS8的注册方法，API中有下面这个方法：
// Registering UIUserNotificationSettings more than once results in previous settings being overwritten.
- (void)registerUserNotificationSettings:(UIUserNotificationSettings*)notificationSettings NS_AVAILABLE_IOS(8_0);
第一步：创建本地推送
第二步：接收本地推送
第三步：解除本地推送
过程中可能会出现如下状况：
Attempting to schedule a local notification……with a sound but haven't received permission from the user to play sounds
Attempting to schedule a local notification……with an alert but haven't received permission from the user to display alerts
可能是因为你没有注册，或者设置中没有开启推送功能
