What data type should I use when converting a byte array from Swift to Objective-C

Question

I have a project where I write the production code in Swift and my unit tests in Objective-C (because I'm using OCMock I write my tests in Objective-C).

What I'm trying to do is to write a Buffer object where the writeBytes method takes a Byte array and a length, like this:

func writeBytes(data: [Byte], length: Int)

In my unit test target I want to test this method, but the problem is that it won't convert this method to Objective-C. By looking in my -Swift.h file I see the following:

@interface Buffer : Object
@property (nonatomic) NSInteger capacity;
@property (nonatomic) NSInteger size;
- (instancetype)initWithCapacity:(NSInteger)capacity OBJC_DESIGNATED_INITIALIZER;
- (void)reset;
- (NSInteger)size;
- (BOOL)isFilled;
- (BOOL)isEmpty;
@end

As you can see the writeBytes method is missing. I've tried different data types to see if it appears: UInt8, UnsafePointer<UInt8>, but none of them work.

For the sake of debugging I tried using a String array and that gets converted to Objective-C without any problems.

What data type should I use for my Byte array to make the writeBytes method available in Objective-C?

Yes, since it is working with String arrays I know the file gets updated. — Markus Persson
– Markus Persson, Commented Jul 17, 2014 at 8:51

Martin R · Accepted Answer · 2014-07-17 11:45:16Z

3

The Swift type [Byte] is not representable in Objective-C, but you can work with a pointer to the bytes:

func writeBytes(data: ConstUnsafePointer<Byte>, length: Int) { ... }

var data : [Byte] = [1, 2, 3]
writeBytes(data, length: data.count)

This mapped to Objective-C as

- (void)writeBytes:(Byte const *)data length:(NSInteger)length;

so that you can call it like

Byte data[] = {1, 2, 3};
[buffer writeBytes:data length:3];

answered Jul 17, 2014 at 11:45

Martin R

541k98 gold badges1.3k silver badges1.4k bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Markus Persson Over a year ago

Ah, nice! This works, thank you! I only tested it with [UnsafePointer<Byte>] and not as you suggested.

Martin R Over a year ago

@Downvoter: It would be helpful to know what is wrong about this answer, so that I can fix it if necessary ...

Community · Accepted Answer · 2017-05-23 11:51:41Z

1

Use NSData. You can create one from an array of [UInt8] in Swift as:

import Foundation
var u8s = [UInt8]()
// ...
var data = NSData(bytes:&u8s, length:u8s.count)

FYI this is the opposite of Swift - converting from ConstUnsafePointer<()> where the questioner was looking for the way to convert NSData to [UInt8].

edited May 23, 2017 at 11:51

CommunityBot

11 silver badge

answered Jul 21, 2014 at 16:05

dankogai

1,63712 silver badges7 bronze badges

Collectives™ on Stack Overflow

What data type should I use when converting a byte array from Swift to Objective-C

2 Answers 2

2 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related