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?

Answer 1

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.

Answer 2

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"

Answer 3

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...