How can I exchange various type's data through NSData?

Question

I'm creating a bluetooth match game application. I'm using func session(session: MCSession, didReceiveData data: NSData, fromPeer peerID: MCPeerID) on MCSessionDelegate.

I want to exchange various type's data, like GameStatusClass, PlayerClass, EnemyClass, CGPoint etc, case by case. Then this is my code. I think, my code is not good because unarchiveObjectWithData is called twice.

Do you have some idea to write simply or nice sample code?

enum ModelType {
    case A
    case B
}

class BasicModel: NSObject {
    var modelType : ModelType?
}
class ModelA: BasicModel {
    var x = 100
    override init() {
        super.init()
        self.modelType = ModelType.A
    }
}
class ModelB: BasicModel {
    var y = "test"
    override init() {
        super.init()
        self.modelType = ModelType.B
    }
}


class NearbyManager : NSObject, MCSessionDelegate {
    func session(session: MCSession, didReceiveData data: NSData,
        fromPeer peerID: MCPeerID)  {
            dispatch_async(dispatch_get_main_queue()) {
                let tmp = NSKeyedUnarchiver.unarchiveObjectWithData(data) as! BasicModel
                switch tmp.modelType! {
                case ModelType.A:
                    let a = NSKeyedUnarchiver.unarchiveObjectWithData(data) as! ModelA
                    self.funcA(a)
                case ModelType.B:
                    let b = NSKeyedUnarchiver.unarchiveObjectWithData(data) as! ModelB
                    self.funcB(b)
                }
            }
    }
    func funcA(data: ModelA) {
        print(data.x)
    }
    func funcB(data: ModelB) {
        print(data.y)
    }
}

Answer 1

A possible solution:
Creation:
• Create a NSData with the model type.
• Archive your Object to NSData.
• Append the two data.

Reading:
• Read the first octet for getting the type.
• Unarchive the rest (with offset).

In Objective-C, but it should be easily translated in Swift (code not tested, but you should get the logic)

//Sending:

NSData *typeData = [NSData dataWithBytes:&ModelTypeA length: sizeof(uint_16)];
NSData *objectData = [NSKeyedArchiver archivedDataWithRootObject:objectA];
NSMutableData *dataToSend = [[NSMutableData alloc] init];
[dataToSend appendData:typeData];
[dataToSend appendData:objectData];

//Reading:

if ([data length] > 1)
{
    NSData *typeData = [data subdataWithRange:NSMakeRange(0,1)];
    uint_16 type;
    [typeData getBytes:type];
    NSData *objectData = [data subdataWithRange:NSMakeRange(1, [data length]-1];
    switch (type)
    {
        case ModelTypeA:
        {
            ModelA *a = (ModelA *)[NSKeyedUnarchiver unarchiveObjectWithData:objectData];
            [self func:a];
        }
            break;
        case ModelTypeB:
        {
            ModelB *b = (ModelB *)[NSKeyedUnarchiver unarchiveObjectWithData:objectData];
            [self func:b];
        }
            break;
        default:
            break;
    }
}

Note: I put the offset to 1, but if you want more and more possible values, you may want to get a bigger offset, but that should be enough kind of object already.