How can I create the correct player object based on a type in a network message?

Question

I am using lidgren as a networking library for a small XNA game. I am using a client/server architecture for the game. Currently, I have the client and server connecting but I would like to be able to pass an enum with a character type when the client requests to join the server. Here is a sample of my code:

while ((inMsg = networkManager.ReadMessage()) != null)
        {

            switch (inMsg.MessageType){
                case NetIncomingMessageType.StatusChanged:
                    switch ((NetConnectionStatus)inMsg.ReadByte()){
                        case NetConnectionStatus.Connected:
                            if (!this.isHosting)
                            {
                              //Extract player info from message and create a local player                             
                            }break;
                        case NetConnectionStatus.RespondedAwaitingApproval:
                            pType = (PlayerType)inMsg.ReadByte();
                            playerManager.AddPlayer(pType);
                            //Then I will send the player information to the client
                            inMsg.SenderConnection.Approve();
                            break;
                    }
                    break;

            }

            this.networkManager.Recycle(inMsg);
        }

When server gets a message with RespondedAwaitingApproval flag, I would like to be able to read the message, extract the type and create an instance of a player of that type. How can I accomplish that?

Answer 1

What's wrong with the simple approach? Something like:

Player CreatePlayerOfType (PlayerType type) {
  switch (type) {
    case PlayerType.Red:
      return new RedPlayer();
    case PlayerType.Blue:
      return new BluePlayer();
    default:
      throw new InvalidOperationException("Unexpected player type.");
  }
}

It's not clear from your question whether different player type enum values correspond to actual different player classes or just instances with different data (which is probably the approach I'd vote for, but I don't know anything else about the nature of your game). However, whichever it is, the above approach will work fine.

If construction of your players becomes complicated or you have a lot of player types or permutations, the above code can present a maintainability problem as it scales. To handle that, you can build your implementation towards an abstract factory pattern, which can afford you some interesting options for data-driving your player creation, or at least keeping the maintenance overhead down.

Answer 2

I have just solved the question by doing the following:

I pass in the player type with the netClient.Connect() method.

NetOutgoingMessage hailMsg = netClient.CreateMessage();
hailMsg.Write((byte)playerType);
netClient.Connect(ipEndPoint,hailMsg);

Then, on the server side, I did the following:

case NetConnectionStatus.RespondedAwaitingApproval:
     PlayerTypesTypes playerType = (PlayerTypes)inMsg.SenderConnection.RemoteHailMessage.ReadByte();
     //Do whatever you want with the playertype
     inMsg.SenderConnection.Approve();
     break;

Basically, I just realised that you could send additional information along with the clients hail message in the netClient.Connect method and that you can extract that from the hail message by specifying SenderConnection.RemoteHailMessage.