NSData from Byte array in Swift

Question

I'm trying to create an NSData var from an array of bytes.

In Obj-C I might have done this:

NSData *endMarker = [[NSData alloc] initWithBytes:{ 0xFF, 0xD9 }, length: 2]

I can't figure out a working equivalent in Swift.

Answer 1

NSData has an initializer that takes a bytes pointer: init(bytes: UnsafeMutablePointer <Void>, length: Int) . An UnsafePointer parameter can accept a variety of different things, including a simple Swift array, so you can use pretty much the same syntax as in Objective-C. When you pass the array, you need to make sure you identify it as a UInt8 array or Swift's type inference will assume you mean to create an Int array.

var endMarker = NSData(bytes: [0xFF, 0xD9] as [UInt8], length: 2)

You can read more about unsafe pointer parameters in Apple's Interacting with C APIs documentation.

Answer 2

var foo : Byte[] = [0xff, 0xD9]

var data = NSData(bytes: foo, length: foo.count)

println("\(data)")

outputs: ff d9

var data = NSData(bytes: [0xFF, 0xD9] as Byte[], length: 2)

println("\(data)")

outputs: ff d9

Edit: Ah, you have to write 'as Byte[]', so then the results are the same

---

UPDATED for Swift 2.2

var foo:[UInt8] = [0xff, 0xD9]
var data = NSData(bytes: foo, length: foo.count)
print("\(data)")

outputs: ff d9

var data = NSData(bytes: [0xFF, 0xD9] as [UInt8], length: 2)
print("\(data)")

outputs: ff d9

Answer 3

You don't need to extend Data, in Swift 3 you can do this:

let bytes:[UInt8] = [0x00, 0x01, 0x02, 0x03]
let data = Data(bytes: bytes)
print(data as NSData)

Prints "<00010203>"

To get the byte array again:

let byteArray:[UInt8] = [UInt8](data)

Answer 4

Swift 3 extension

extension Data {

    init<T>(fromArray values: [T]) {
        var values = values
        self.init(buffer: UnsafeBufferPointer(start: &values, count: values.count))
    }

    func toArray<T>(type: T.Type) -> [T] {
        return self.withUnsafeBytes {
            [T](UnsafeBufferPointer(start: $0, count: self.count/MemoryLayout<T>.stride))
        }
    }
}

Usage

let bytes:[UInt8] = [0x00, 0xf4, 0x7c]
let data = Data(fromArray: someBytes)
print(data as NSData)

let bytes = data.toArray(type: UInt8.self)
print(bytes)

Answer 5

Answer in Swift 5 is simple and not found here. Ran into this issue and found answer:

var bytes = [Int8](repeating: 0, count: 32)
let data = Data(bytes: bytes, count: bytes.count)

Answer 6

For Swift 5 I have created another Data extension that works well.

extension Data {

    init<T>(fromArray values: [T]) {
        var values = values
        self.init(buffer: UnsafeBufferPointer(start: &values, count: values.count))
    }

    func toArray<T>(type: T.Type) -> [T] {
        let value = self.withUnsafeBytes {
            $0.baseAddress?.assumingMemoryBound(to: T.self)
        }
        return [T](UnsafeBufferPointer(start: value, count: self.count / MemoryLayout<T>.stride))
    }

}

Sample Usage

let data = Data(fromArray: [1, 2, 3, 4, 5])
let array = data.toArray(type: Int.self)
print(array)
// [1, 2, 3, 4, 5]