Objective c 中获取GUID

+ (NSString*) stringWithUUID 

{
   CFUUIDRefuuidObj = CFUUIDCreate(nil);//create a new UUID
   
   //get the string representation of the UUID
   NSString*uuidString = (NSString*)CFUUIDCreateString(nil, uuidObj);
   CFRelease(uuidObj);
   return [uuidString autorelease];
}