Extract struct from NSData in Swift

问题:

I'm making Game Center game. I send a data packet containing a struct MovePacket like this:

var packet = MovePacket(packetID: 1, move: myMove)

let dataPacket = NSData(bytes: &packet, length: sizeof(MovePacket))

currentMatch!.sendDataToAllPlayers(dataPacket, withDataMode: GKMatchSendDataMode.Reliable, error: nil)

This works like in Objective-C, but I don't understand how to decode the received NSData back to my struct MovePacket. This is one of my tries:

func match(match: GKMatch!, didReceiveData data: NSData!, fromRemotePlayer player: GKPlayer!) {

    var packet : MovePacket 

    data.getBytes(&packet, length: sizeof(MovePacket)) // getting error here: Address of variable 'packet' taken before it is initialized

    println(packet) //Variable 'packet' used before being initialized

}

回答1:

Assuming you meant “decode it back from NSData”:

func match(match: GKMatch!, didReceiveData data: NSData!, fromRemotePlayer player: GKPlayer!) {
    if data.length == sizeof(MovePacket) {
        let packet = UnsafePointer<MovePacket>(data.bytes).memory
        println(packet)
    } else {
        // error: data size is incorrect
    }
}