How to convert NSUUID to NSData

NSUUID *vendorIdentifier = [[UIDevice currentDevice] identifierForVendor];
uuid_t uuid;
[vendorIdentifier getUUIDBytes:uuid];

NSData *vendorData = [NSData dataWithBytes:uuid length:16];

Use this to get the vendorIdentifier as Data (Swift 4):

var uuidBytes = UIDevice.current.identifierForVendor!.uuid
let uuidData = NSData(bytes: &uuidBytes, length: 16) as Data

Keep in mind to guard against UIDevice.current.identifierForVendor being nil as the documentation says.

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Original answer (Swift 2 Version):

var uuidBytes: [UInt8] = [UInt8](count: 16, repeatedValue: 0)
UIDevice.currentDevice().identifierForVendor!.getUUIDBytes(&uuidBytes)
let uuidData = NSData(bytes: &uuidBytes, length: 16)

Swift 3 Version:

let vendorId = UIDevice.current.identifierForVendor!
let uuidBytes = Mirror(reflecting: vendorId.uuid).children.map { $0.1 as! UInt8 }
let data = Data(bytes: uuidBytes)