Get singleton instance in swift

Question

I've written a class in objective-c to get me a single instance of class called helper which helps me to do a lot of different stuff.

static Helper *objHelper = nil;

@implementation Helper

- (id)init {
    self = [super init] ;
    return self;
}

///- Return Helper Singleton Instance
+ (Helper *) getHelperInstance;
{
    @synchronized (objHelper) {
        if ( !objHelper || objHelper == NULL ) {
            objHelper = [[Helper alloc] init];
        }
        return objHelper;
    }
}

I've tried to write it in swift but i don't think i made it right:

var objHelper : Helper?


override init() {
    super.init()

}

func getHelperInstance() ->Helper{

    synchronizd(objHelper == nil) {

        if objHelper == nil {

            objHelper = Helper()
        }
    }
    return objHelper!

}

and to handle synchronized :

func synchronizd(lock: AnyObject, closure:()->()) {
    objc_sync_enter(lock)
    closure()
    objc_sync_exit(lock);
}

When i used the objective-c class i use it in my classes as :

var objHelper = Helper()
objHelper  = Helper.getHelperInstance()

but when i wrote it in swift which i have to pass parameters :

var objHelper = Helper()
objHelper  = Helper.getHelperInstance(objHelper)()

What did i converted to swift wrong ? and why its asking for (objHelper)() where when it was in objective c code it didn't ask to do that ! i just need to make my swift code runs the same as my objective-c code.

Update: i am asking of doing the singleton on another way instead of struct or whatever.my code works fine with some edits in swift and thats what in asking for.

It is far easier in Swift, have a look at stackoverflow.com/questions/24024549/…. — Martin R
– Martin R, Commented Dec 28, 2015 at 8:12
@MartinR , if I've defined class Helper { static let sharedInstance: Helper = Helper() private init() { print("AAA"); } } then how do i use it in other classes ? i need to do like let x = Helper. sharedInstance ? — Nata Mio
– Nata Mio, Commented Dec 28, 2015 at 8:43
Where is the problem? That should work (if you remove the space character in Helper. sharedInstance). — Martin R
– Martin R, Commented Dec 28, 2015 at 10:35

Erez Hod · Accepted Answer · 2015-12-28 11:11:56Z

4

In Swift it is extremely simple, keep a shared instance constant with the class reference inside the class itself like so:

class Helper {
    static let sharedInstance = Helper()

    func someMethod() {
        print("Bla bla")
    }
}

And use its methods in different classes like so:

Helper.sharedInstance.someMethod()

edited Dec 28, 2015 at 11:11

answered Dec 28, 2015 at 9:03

Erez Hod

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2 Comments

Martin R Over a year ago

This does not compile and does not implement a "shared instance" because you forgot to make the property static. Correct implementations can be found here: stackoverflow.com/questions/24024549/….

Luca Angeletti Over a year ago

You should make the default init private. Please add this code private init() {}

Marius Fanu · Accepted Answer · 2015-12-28 08:53:10Z

0

It's this simple:

// This will be a global variable accessible from anywhere
let helperSharedInstance = Helper()

class Helper {

}

answered Dec 28, 2015 at 8:53

Marius Fanu

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9 Comments

Luca Angeletti Over a year ago

This is not a Singleton Class

Marius Fanu Over a year ago

@appzYourLife there's no such thing as a Singleton Class. Singleton is a design pattern, and you can implement it in multiple ways, either like I did it or like the other people suggested via a static variable on a class.

Nata Mio Over a year ago

@appzYourLife , Then is it possible for you to translate my objective-c code into swift for singleton class ? Swift way is complicated to implement.

Luca Angeletti Over a year ago

@MariusFanu:

[...] The singleton pattern is implemented by creating a class with a method that creates a new instance of the class if one does not exist. If an instance already exists, it simply returns a reference to that object.

Wikipedia. I can't see such a mechanism provided by your code. It's up to the developer using the global constant and avoiding the initialization of a new Helper. So I don't think your code is a valid implementation of the Singleton Design Pattern.

Marius Fanu Over a year ago

@appzYourLife That's just one way to implement it. If you scroll down, on that same wiki page, you'll see The enum way, which is not a class. A Singleton, must be accessible and point to that same instance, both things my example does.

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