How to convert an Int into NSData in Swift?

With Swift 3.x to 5.0:

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

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.load(as: Int.self)
}

---

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.load(as: Int.self).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.load(as: Int.self).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.

You can convert in this way:

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

For any integer type:

extension FixedWidthInteger {
    var data: Data {
        let data = withUnsafeBytes(of: self) { Data($0) }
        return data
    }
}

Example:

let data = 1.data