Accessing Obj-C properties in Swift extension file

Question

I started writing Swift extensions on my view controllers. So I have three files right now:

My header file, ViewController.h:

@interface MyViewController : UIViewController

@end

My Obj-C implementation file, ViewController.m:

@interface MyViewController () <UIScrollViewDelegate>
@property (strong, nonatomic) UIScrollView *scrollView;
@end

@implementation MyViewController

- (void)viewDidLoad {

    [super viewDidLoad];

    self.scrollView = [[UIScrollView alloc] init];
    [self customiseScrollView]; //This is Swift method called from Obj-C file
}

@end

And finally, ViewController.swift:

extension MyViewController {

    func customiseScrollView() {

    }
}

My question is, is it possible to access my Obj-C properties from my Swift implementation file? Every time I refer to it, I got an error:

Value of type 'MyViewController' has no member 'scrollView'

Bonus 1: Can someone also clarify if the Swift component can see what the .m is a delegate of as well. (To clarify, doing scrollView.delegate = self in Swift is a compile error because the Swift file does not realise that the .m file is a UIScrollViewDelegate).

Bonus 2: Can Swift extension file call Obj-C methods that are declared from the .m counterpart?

If you want to access the scrollView property from Swift then you should put it into the public interface in the .h file. – Re Bonus 1: *"what the .m is a delegate of"* makes no sense. A delegate is an object, not a file. – Re Bonus 2: Yes, [How to call Objective C code from Swift](http://stackoverflow.com/questions/24002369/how-to-call-objective-c-code-from-swift) is #2 on the frequent tab of the [swift] questions. — Martin R, Oct 22 '15 at 07:52
@MartinR Thanks Martin, I edited that part of the question to clarify what I meant. I also realised that I can access the properties when I put it in .h file, but I didn't want to do that because that exposes the property to my other Obj-C classes too. — Enrico Susatyo, Oct 22 '15 at 08:08
Declarations in the .m file are only visible in that file. The same would happen if you define an extension in a separate Objective-C file, it is not a Swift issue. — Martin R, Oct 22 '15 at 08:12

Kubba · Accepted Answer · 2019-08-29T17:57:52.920

17

I think that you can't access private properties from extension. Your scrollView property is in .m file, not .h - which means it's private and it's not visible from extension file.

Solution: move

@property (strong, nonatomic) UIScrollView *scrollView;

to your header file.

edited Aug 29 '19 at 17:57

answered Oct 22 '15 at 07:56

Kubba

3,390
19
34

1

Yes, this works! But I was hoping I don't have to do this, because I don't want these properties to be accessible from my other Obj-C classes. – Enrico Susatyo Oct 22 '15 at 08:09
4

@EnricoSusatyo It might be a good idea to make it `readonly` in the header and `readwrite` only in the implementation file. – Sulthan Dec 26 '18 at 15:49

Nico Spencer · Answer 2 · 2018-12-26T17:49:31.317

You can access internal objc properties and methods if you declare the objc class extension in a separate header and include that header in the bridging header.

MyClass.h

@interface MyClass : NSObject

@property (nonatomic, copy, readonly) NSString *string;

@end

MyClass+Private.h

#import "MyClass.h"

@interface MyClass ()

@property (nonatomic, copy) NSString *string;

@end

MyClass.m

#import "MyClass+private.h"

@implementation MyClass

//...

@end

Project-Bridging-Header.h

#import "MyClass.h"
#import "MyClass+Private.h"

Milos · Answer 3 · 2015-10-22T08:18:41.763

In Swift, private properties are not accessible from another file. This is the meaning of private in Swift. For example:

file1.swift

class MyClass {
    private var privateProperty: String = "Can't get to me from another file!"
}
extension MyClass: CustomStringConvertible {
    var description: String {
        return "I have a `var` that says: \(privateProperty)"
    }
}

file2.swift

extension MyClass {
    func cantGetToPrivateProperties() {
        self.privateProperty // Value of type 'MyClass' has no memeber 'privateProperty'
    }
}

A property declared in the implementation of an Objective-C class is a private property. As such, the property cannot be accessed from a Swift extension since this will be necessarily from a different (.swift) file...

Note that in your example, conformance to a delegate protocol is also declared privately, so this will not be visible from a Swift extension for the same reason. Likewise with private methods... However, if your `scrollView` takes part in a window hierarchy, you could get to it through its `public`ly or `internal`ly declared superview... — Milos, Oct 22 '15 at 08:28

score -1 · Answer 4 · answered Oct 22 '15 at 07:51

You can. All you need is to create a bridging objective C header.

Per Apple Documentation:

To import a set of Objective-C files in the same app target as your Swift code, you rely on an Objective-C bridging header to expose those files to Swift. Xcode offers to create this header file when you add a Swift file to an existing Objective-C app, or an Objective-C file to an existing Swift app.

score -1 · Answer 5 · answered Oct 22 '15 at 07:51

-1

Just create a Bridging-Header file and later import your ObjC file in it, like:

#import <objectivec.h>

Later in your swift file:

var a = objectivec()
a.method_from_those_file

For more information read Apple Doucmentation from here.

answered Oct 22 '15 at 07:51

Orkhan Alizade

7,379
14
40
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Accessing Obj-C properties in Swift extension file

5 Answers5