Using Swift Shared Instance in Objective C

Question

I have a shared instance of a class in Swift that I'm using in Objective-C. I'm unable to create the shared instance and use the instance function. Here's my Swift code.

class VideoPlayerSignaler: NSObject {
    static let sharedInstance = VideoPlayerSignaler()

    let playerAction = Signal<PlayerAction>()

    private override init() {

    }

    func firePlayerAction(action: PlayerAction) {
        playerAction.fire(action)
    }
}

Here's my Objective-C code.

VideoPlayerSignaler *signaler = [VideoPlayerSignaler sharedInstance];

// This is the line that is producing the issue. 
// It's as if the signaler variable is a Class Instance
[signaler firePlayerAction: PlayerAction.Stop];

The error I'm producing states that firePlayerAction does not exist. In essence, Objective C believes the signaler variable to be a class instance.

What am I doing wrong and how do I fix it so that signaler is a shared instance of VideoPlayerSignaler?

If you post your code for the signal class as well as the firstPlayerAction in Objective-C, I may be able to help. — dhint4
– dhint4, Commented Oct 21, 2015 at 3:50
I can give you the library code. https://github.com/artman/Signals — thank_you
– thank_you, Commented Oct 21, 2015 at 3:58
That's what I thought. XCode doesn't recognize the function or the instance variable. — thank_you
– thank_you, Commented Oct 21, 2015 at 4:09

rickster · Accepted Answer · 2015-10-21 19:26:24Z

There's nothing wrong with your Swift, or with how you access the singleton instance from ObjC — the problem is the enum value you're passing to it.

Presumably your enum declaration looks something like this:

enum PlayerAction: Int {
    case Stop, Collaborate, Listen // etc
}

To make your enum accessible to ObjC, you need to preface the declaration with @objc:

@objc enum PlayerAction: Int { /*...*/ }

This makes it appear as a Cocoa-style NS_ENUM declaration in ObjC, creating global symbols for case names by concatenating the Swift enum type's name with the case names:

typedef NS_ENUM(NSInteger, PlayerAction) {
    PlayerActionStop = 1,
    PlayerActionCollaborate,
    PlayerActionListen, // etc
};

So those names are what you should be passing when you call a method taking an enum value from ObjC:

[signaler firePlayerAction: PlayerActionStop]; // NOT PlayerAction.Stop

(The only docs I can find to cite for this are buried in the Attributes chapter in The Swift Programming Language — scroll down the to objc attribute.)

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