Implementing Objective C delegate in Swift

Question

I have a Objective C class that has methods that look like this:

@class Client;

@protocol ClientDelegate <NSObject>

@optional
-(void) receivedMessageFromClient : (id) message;

@end

@interface Client : NSObject 

+(id) setup; 
 @property(nonatomic, strong) id <ClientDelegate> clientDelegate;

// more method declarations below

I am implementing the ClientDelegate in my Swift class like this:

class HomeViewController: UIViewController, ClientDelegate {
    var client : AnyObject?
    var delegate: ClientDelegate?

    override func viewDidLoad() {
        super.viewDidLoad()

        client = Client.setup() as! Client
         client.clientDelegate = self
    }

func receivedMessageFromClient(message: AnyObject) {
        print("Message recieved: \(message)")
    }
}

This is giving me a compiling error:

Cannot assign to property: 'self' is immutable

When I remove the lines

client = Client.setup() as! Client
client.clientDelegate = self

the code compiles and calls the method in the Client class that in turns sends a message to receivedMessageFromClient, but the method is not called in HomeViewController. It seems that everything is setup with the exception of assigning self to be the delegate.

Delegates usually have weak attribute instead of strong. And RTFM about protocols developer.apple.com/library/ios/documentation/Swift/Conceptual/… — Alexmelyon
– Alexmelyon, Commented Nov 20, 2015 at 8:24
Possible duplicate of I am using objective-c classes in swift2 , how i can implement delegate methods and bind that delegate — Janak LN
– Janak LN, Commented Nov 20, 2015 at 8:29
yes, and it is working. I am able to call and use methods of the class — Ashish Agarwal
– Ashish Agarwal, Commented Nov 20, 2015 at 9:12
Reading your code, I think you need to revise the delegation pattern check this out. You first need to sort out your delegate in objective c then implement it in Swift. — Rob Sanders
– Rob Sanders, Commented Nov 20, 2015 at 9:16

Mike Lischke · Accepted Answer · 2018-01-05 07:45:44Z

11

Check out my comments on your question but this is a basic example of an Objective-C delegate implemented in Swift:

Objective-C:

@protocol MyDelegate <NSObject>

@optional
- (void)canImplementThis:(int)aVar;
@required
- (BOOL)needToImplementThis;

@end

@interface MyClass : NSObject

@property (nonatomic, weak) id<MyDelegate> delegate;

@end

Swift:

class SwiftClass : UIViewController, MyDelegate {

    var myObj : MyClass?

    override func viewDidLoad() {
        super.viewDidLoad()

        myObj = MyClass()
        myObj?.delegate = self
    }

    // MARK: - <MyDelegate>

    func canImplementThis(aVar : Int) {
        print("Called: \(aVar))
    }

    func needToImplementThis() -> Bool {
        return false
    }

}

Forgive any typos I typed this out straight into SO.

edited Jan 5, 2018 at 7:45

Mike Lischke

54.4k18 gold badges142 silver badges210 bronze badges

answered Nov 20, 2015 at 9:31

Rob Sanders

5,4253 gold badges35 silver badges61 bronze badges

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

1 Comment

user924 Over a year ago

how to call needToImplementThis or canImplementThis in objective-c?

Goose · Accepted Answer · 2017-11-09 21:49:08Z

0

Had to change Int to Int32 for some reason so it fix the invalid selector issue, with Int32 on the swift side but then worked

answered Nov 9, 2017 at 21:49

Goose

1

Collectives™ on Stack Overflow

Implementing Objective C delegate in Swift

2 Answers 2

1 Comment

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related