How to initialise a string from NSData in Swift

Question

I have been trying to initialise a string from NSData in Swift.

In the NSString Cocoa Documentation Apple is saying you have to use this:

 init(data data: NSData!, encoding encoding: UInt)

However Apple did not include any example for usage or where to put the init.

I am trying to convert the following code from Objective-C to Swift

NSString *string;
string = [[NSString alloc] initWithData: data encoding: NSUTF8StringEncoding];

I have been trying a lot of possible syntaxes such as the following (of course it did not work):

var string:NSString!
string = init(data: fooData,encoding: NSUTF8StringEncoding)

Sunkas · Answer 1 · 2017-02-23T14:59:13.077

282

This is the implemented code needed:

in Swift 3.0:

var dataString = String(data: fooData, encoding: String.Encoding.utf8)

or just

var dataString = String(data: fooData, encoding: .utf8)

Older swift version:

in Swift 2.0:

import Foundation

var dataString = String(data: fooData, encoding: NSUTF8StringEncoding)

in Swift 1.0:

var dataString = NSString(data: fooData, encoding:NSUTF8StringEncoding)

edited Feb 23 '17 at 14:59

answered Apr 02 '15 at 08:28

Sunkas

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Swift 2 has a different way of doing this – Lucas van Dongen Nov 03 '15 at 19:47
3

Added a Swift 2.0 version as well now – Sunkas Nov 09 '15 at 08:50
Would you happen to know the Swift 3.0 way? `error: use of unresolved identifier 'NSUTF8StringEncoding'` – Glenn 'devalias' Grant Jun 22 '16 at 01:14
2

Added a Swift 3.0 version as well. Damn, Apple like changing stuff! – Sunkas Jun 22 '16 at 14:09
Does swift have an "#ifdef" to make the code support both versions? – elcuco Jun 30 '16 at 07:35
There is #if #else #elseif, try those – Sunkas Jun 30 '16 at 08:32
1

You have to compile against a specific version of Swift, so your code will all be written against either 2.x or 3.x. Also, note with the 3.0 version you can shorten it by using `var dataString = String(data: fooData, encoding: .utf8)`. – ruttopia Jul 20 '16 at 18:17

score 228 · Accepted Answer · edited May 18 '17 at 19:43

228

This is how you should initialize the NSString:

Swift 2.X or older

let datastring = NSString(data: fooData, encoding: NSUTF8StringEncoding)

Swift 3 or newer:

let datastring = NSString(data: fooData, encoding: String.Encoding.utf8.rawValue)

This doc explains the syntax.

edited May 18 '17 at 19:43

MCCCS

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answered Jun 03 '14 at 19:26

67cherries

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2

Note that you don’t need to repeat “data” and “encoding” like that. – jbg Jul 07 '14 at 05:36
2

How can you do that what UInt is a constructor? It's asking me to add brackets. – User Sep 20 '14 at 02:36
19

Should be `let datastring = NSString(data: fooData, encoding:NSUTF8StringEncoding)` – Yas Tabasam Apr 15 '15 at 21:03
14

Is it possible to convert `NSData` directly into a Swift `String` (instead of an `NSString`)? – ma11hew28 Jun 29 '15 at 18:45
3

@MattDiPasquale var swiftString = NSString(data: NSData!, encoding: UInt) as! String that's all – Gintama Aug 29 '15 at 06:52
12

@MattDiPasquale Ignore the above forced cast; `String` is an `NSString`... all of these should be: `var datastring = String(data: someData, encoding: NSUTF8StringEncoding)` – JRaymond Oct 30 '15 at 00:27
@JRaymond NSLog would reject it as argument if you don't cast it. – marsbear Aug 24 '16 at 13:34

Can · Answer 3 · 2015-09-30T18:41:48.457

Swift 2.0

It seems that Swift 2.0 has actually introduced the String(data:encoding:) as an String extension when you import Foundation. I haven't found any place where this is documented, weirdly enough.

(pre Swift 2.0) Lightweight extension

Here's a copy-pasteable little extension without using NSString, let's cut the middle-man.

import Foundation

extension NSData
{
    var byteBuffer : UnsafeBufferPointer<UInt8> { get { return UnsafeBufferPointer<UInt8>(start: UnsafeMutablePointer<UInt8>(self.bytes), count: self.length) }}
}

extension String
{
    init?(data : NSData, encoding : NSStringEncoding)
    {
        self.init(bytes: data.byteBuffer, encoding: encoding)
    }
}

// Playground test
let original = "Nymphs blitz quick vex dwarf jog"
let encoding = NSASCIIStringEncoding

if let data = original.dataUsingEncoding(encoding)
{
    String(data: data, encoding: encoding)
}

This also give you access to data.byteBuffer which is a sequence type, so all those cool operations you can do with sequences also work, like doing a reduce { $0 &+ $1 } for a checksum.

Notes

In my previous edit, I used this method:

var buffer = Array<UInt8>(count: data.length, repeatedValue: 0x00)
data.getBytes(&buffer, length: data.length)
self.init(bytes: buffer, encoding: encoding)

The problem with this approach, is that I'm creating a copy of the information into a new array, thus, I'm duplicating the amount of bytes (specifically: encoding size * data.length)

score 4 · Answer 4 · edited Jan 09 '17 at 03:17

4

Since the third version of Swift you can do the following:

let desiredString = NSString(data: yourData, encoding: String.Encoding.utf8.rawValue)

simialr to what Sunkas advised.

edited Jan 09 '17 at 03:17

Dani Pralea

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answered Dec 12 '16 at 08:29

Sergei Petrachkov

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score 3 · Answer 5 · answered Jun 03 '14 at 19:30

3

import Foundation
var string = NSString(data: NSData?, encoding: UInt)

answered Jun 03 '14 at 19:30

mlask

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score 2 · Answer 6 · answered Jun 02 '16 at 12:37

Another answer based on extensions (boy do I miss this in Java):

extension NSData {
    func toUtf8() -> String? {
        return String(data: self, encoding: NSUTF8StringEncoding)
    }
}

Then you can use it:

let data : NSData = getDataFromEpicServer()
let string : String? = data.toUtf8()

Note that the string is optional, the initial NSData may be unconvertible to Utf8.

Tarun Seera · Answer 7 · 2016-03-16T14:01:20.703

Objective - C

NSData *myStringData = [@"My String" dataUsingEncoding:NSUTF8StringEncoding]; 
NSString *myStringFromData = [[NSString alloc] initWithData:myStringData encoding:NSUTF8StringEncoding];
NSLog(@"My string value: %@",myStringFromData);

Swift

//This your data containing the string
   let myStringData = "My String".dataUsingEncoding(NSUTF8StringEncoding)

   //Use this method to convert the data into String
   let myStringFromData =  String(data:myStringData!, encoding: NSUTF8StringEncoding)

   print("My string value:" + myStringFromData!)

http://objectivec2swift.blogspot.in/2016/03/coverting-nsdata-to-nsstring-or-convert.html

How to initialise a string from NSData in Swift

7 Answers7

in Swift 3.0:

Swift 2.0

(pre Swift 2.0) Lightweight extension

Notes

Linked