Swift Generic Class implementing an Objective-C Protocol

Question

My intention is to create a generic class in Swift which conforms to an Objective-C protocol:

The class is:

class BaseViewFactoryImpl<T> : NSObject, BaseView {
  func getNativeInstance() -> AnyObject {
    return String("fsd")
  }
}

The protocol BaseView is:

@protocol BaseView < NSObject >

- (id)getNativeInstance;

@end

The compiler tells me:

Type 'BaseViewFactoryImpl<T>' does not conform to protocol 'BaseView'

If I delete <T> then there is no error.

What is wrong here? How can I get the correct generic class implementation?

It's just not possible with generic classes, see http://stackoverflow.com/questions/26097581/generic-nsoperation-subclass-loses-nsoperation-functionality for a similar issue. — Martin R, Apr 17 '15 at 14:37

score 1 · Answer 1 · answered Feb 02 '16 at 08:43

//BaseViewFactory.swift

class BaseViewFactoryImpl<T> : NSObject, BaseView {
    func getNativeInstance() -> AnyObject {
        return String("fsd")
    }

//BaseViewProtocol.h

@protocol BaseView <NSObject>

- (id)getNativeInstance;

@end

//BridgingHeader.h

#import "BaseClassProtocol.h"

Your code should work. Have you created the bridging header to import the obj-C protocol file?

Cristik · Answer 2 · 2021-06-26T05:00:57.803

1

Starting with Swift 3, you need to use Any, not AnyObject, to represent generic id values coming from Objective-C.

This builds with no errors:

class BaseViewFactoryImpl<T> : NSObject, BaseView {
  func getNativeInstance() -> Any {
    return "fsd"
  }
}

edited Jun 26 '21 at 05:00

answered Sep 26 '19 at 20:48

Cristik

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score 0 · Answer 3 · answered Apr 27 '15 at 02:25

If you create a new generic view model, when you try to create any subclass of the generic view model, you need to declare the subclass as a generic class as well. It's kind of annoy.

For a better way, you can use typealias to declare the instance's type instead of using generic:

protocol BaseView {
    typealias T
    func getNativeInstance() -> T!
}

class StringViewModel : BaseView {

    typealias T = String

    func getNativeInstance() -> String! {
        return T()
    }

}

Swift Generic Class implementing an Objective-C Protocol

3 Answers3