How to convert an Int into NSData in Swift?

问题

In Objective-C I use the following code to

Convert an Int variable into NSData, a packet of bytes.

int myScore = 0;
NSData *packet = [NSData dataWithBytes:&myScore length:sizeof(myScore)];

Use the converted NSData variable into a method.

[match sendDataToAllPlayers: 
packet withDataMode: GKMatchSendDataUnreliable 
error: &error];

I tried converting the Objective-C code into Swift:

var myScore : Int = 0

func sendDataToAllPlayers(packet: Int!,
            withDataMode mode: GKMatchSendDataMode,
            error: NSErrorPointer) -> Bool {

            return true
}

However, I am not able to convert an Int variable into an NSData and use it an a method. How can I do that?

回答1:

With Swift 3.x to 5.0:

var myInt = 77
var myIntData = Data(bytes: &myInt, 
                     count: MemoryLayout.size(ofValue: myInt))

回答2:

In contemporary versions of Swift, I would do:

let score = 1000
let data = withUnsafeBytes(of: score) { Data($0) }

e8 03 00 00 00 00 00 00

And convert that Data back to an Int:

let value = data.withUnsafeBytes {
    $0.bindMemory(to: Int.self)[0]
}

Note, when dealing with binary representations of numbers, especially when exchanging with some remote service/device, you might want to make the endianness explicit, e.g.

let data = withUnsafeBytes(of: score.littleEndian) { Data($0) }

 e8 03 00 00 00 00 00 00

And convert that Data back to an Int:

let value = data.withUnsafeBytes {
    $0.bindMemory(to: Int.self)[0].littleEndian
}

Versus big endian format, also known as “network byte order”:

let data = withUnsafeBytes(of: score.bigEndian) { Data($0) }

 00 00 00 00 00 00 03 e8

And convert that Data back to an Int:

let value = data.withUnsafeBytes {
    $0.bindMemory(to: Int.self)[0].bigEndian
}

Needless to say, if you don’t want to worry about endianness, you could use some established standard like JSON (or even XML).

For Swift 2 rendition, see previous revision of this answer.

回答3:

You can convert in this way:

var myScore: NSInteger = 0
let data = NSData(bytes: &myScore, length: sizeof(NSInteger))

来源：https://stackoverflow.com/questions/28680589/how-to-convert-an-int-into-nsdata-in-swift

标签

ios

swift

int

nsdata