我们在iOS应用程序中使用远程通知,我们正在注册应用程序内的APNS服务器：didFinishLaunching：delegate方法.这意味着每次应用程序刚刚启动时,它都将在APNS服务器上注册.以下是代码段.
[[UIApplication sharedApplication] registerForRemoteNotifications]
我们注意到设备令牌(由APNS服务器交付给我们)每次都是相同的.因此,我们认为我们可以在NSUserDefaults中保存令牌并在以后使用它.在application：didFinishLaunching：方法中,我们可以检查NSUserDefaults中是否存在设备令牌.如果它可用,我们可以使用相同而不是注册到APNS.否则,我们可以选择向APNS注册.
但是,从Apple文档中可以看出,“他们鼓励我们在每次新推出应用程序时注册远程通知”.以下是文档的截图.
设备令牌值何时实际更改？我是否能够将设备令牌存储在NSUserDefaults中并在以后使用它而不是每次都注册？请帮忙！！提前致谢！！
用一些苹果文档回答你的问题：
The form of this phase of token trust ensures that only APNs generates the token which it will later honor,and it can assure
itself that a token handed to it by a device is the same token that it
previously provisioned for that particular device—and only for that
device.
If the user restores backup data to a new device or reinstalls the
operating system,the device token changes.
这意味着您不应该将令牌真正存储在NSUserDefaults中.
但是,如果你想保存它,我建议将它保存在钥匙串中.
请参阅此示例如何执行此操作：
Store Device Token in Keychain
Apple文档的另一个引用：
“By requesting the device token and passing it to the provider every time your application launches,you help to ensure that the provider has the current token for the device. If a user restores a backup to a device other than the one that the backup was created for (for example,the user migrates data to a new device),he or she must launch the application at least once for it to receive notifications again. If the user restores backup data to a new device or reinstalls the operating system,the device token changes. Moreover,never cache a device token and give that to your provider; always get the token from the system whenever you need it. If your application has previously registered,calling registerForRemoteNotificationTypes: results in iOS passing the device token to the delegate immediately without incurring additional overhead.”
编辑：
看起来上面链接到Apple的文档已经打破了.这是一个更新的链接(感谢@Enrico Cupellini)：https://developer.apple.com/library/content/technotes/tn2265/_index.html
