How to call an Objective-C function with a (NSMutableArray *)parameter in Swift?

Question

Created May ’18

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I need to use an Objective-C class in Swift wuith some functions that have NSMutableArray * parameter, as the following example:

@interface StereotacticFrame : NSObject

- (BOOL)sortFiducials :(NSMutableArray *)fiducials :(float)imageWidth;

....

Where fiducials is an in-out parameter.

In Swift class I have the property

var fiducials = NSMutableArray(capacity: 9)

I need to use the Obj-C class like this:

let frame = StereotacticFrame()

frame.sortFiducials(&fiducials, Float(imageView.bounds.size.width))

But I got the following error: '&' used with non-inout argument of type 'NSMutableArray!'

This class perform some complex medical calculations and could be very difficult for me to translate to Swift the whole thing.

What I can do?

Thanks in advance!

PS.: If the & is removed, the program crashes when de function is executed, because "fiducials" is actually an in-out parameter!

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Answer 1

Claude31 OP

May ’18

If I understand well how this works, your objc sortFiducials is imported in Swift as :

func sortFiducials(_ array: fiducials!, imageWidth: Float) -> Bool

then it should be called as

frame.sortFiducials(fiducials, Float(imageView.bounds.size.width))

See OOPer (credit to him) answer here:

h ttps://stackoverflow.com/questions/41274950/swift-method-contain-nsmutablearray-doest-override

0

Answer 2

Elga OP

May ’18

I did a test without the &:

frame.sortFiducials(fiducials, Float(imageView.bounds.size.width))

The program crashes when the function is executed, because "fiducials" is actually an in-out parameter.

It seems that the function is imported assuming that fiducials is not an in-out parameter.

Then, when the Obj-C function tries to change the content of the array, the app crashes.

0

Answer 3

Claude31 OP

May ’18

Have you checked you have no inconsistency between framework and Swift code ?

Can you recompile the framwork ?

0

Answer 4

DTS Engineer OP

Apple

May ’18

Parameters of type

NSMutableArray

don’t get any Swift magic; the importer imports them as

NSMutableArray

. Such arrays are mutable, meaning that the caller can mutate them and you see the results. So, while they can act as in/out parameters they don’t need to be imported into Swift as

inout

parameters, so there’s no ampersand (

) at the call site.

For example, a class like this:

NS_ASSUME_NONNULL_BEGIN

@interface Test : NSObject

- (void)addObject:(id)object toList:(NSMutableArray *)list;

@end

NS_ASSUME_NONNULL_END

is imported in Swift as:

open class Test : NSObject {
    open func add(_ object: Any, toList list: NSMutableArray)
}

and thus you can call it from Swift as:

let t = Test()
let list = NSMutableArray()
list.add("hello")
t.add("cruel", toList: list)
list.add("world")
NSLog("%@", list)

and get output like this:

2018-05-10 13:05:05.259166+0100 xxst[41284:14867763] (
    hello,
    cruel,
    world
)

To investigate this further I recommend that you create a small test project and implement a dummy version of this method in Objective-C and then call it from Swift via a bridging header. That will eliminate the possibility of a header/implementation mismatch, as suggested by Claude31.

If your test project still crashes then you can post snippets of it so that we can see the actual code.

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