iOS Device ID的几种形式

每次启动APP都会变更

NSString *uuid = [[NSUUID UUID] UUIDString]  

每次安装APP都会变更

NSString *idfv = [[UIDevice currentDevice].identifierForVendor UUIDString];  

跟随广告设置，新启动和新安装都不会变更

#import <AdSupport/ASIdentifierManager.h>  
ASIdentifierManager *asIM = [[ASIdentifierManager alloc] init];  
NSString *idfa = [asIM.advertisingIdentifier UUIDString];