获取一个DeviceId

-(NSString*)getDeviceId{
    
    NSString* uuidString = nil;
    if (![[NSUserDefaults standardUserDefaults] objectForKey:@"deviceId"]) {
        
        CFUUIDRef uuidRef = CFUUIDCreate(kCFAllocatorDefault);
        CFStringRef strRef = CFUUIDCreateString(kCFAllocatorDefault, uuidRef);
        uuidString = [NSString stringWithString:(NSString*)strRef];
        
        NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
        [defaults setValue:uuidString forKey:@"deviceId"];
        [defaults synchronize];
        
        CFRelease(strRef);
        CFRelease(uuidRef); 
    }else{
        uuidString = [[NSUserDefaults standardUserDefaults] objectForKey:@"deviceId"];
    }
    
    return uuidString;
}