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 http://stackoverflow.com/questions/24024549/dispatch-once-singleton-model-in-swift. — Martin R, Dec 28 '15 at 08:12
@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, Dec 28 '15 at 08:43
Where is the problem? That should work (if you remove the space character in `Helper. sharedInstance`). — Martin R, Dec 28 '15 at 10:35

Erez Hod · Answer 1 · 2015-12-28T11:11:56.343

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 '15 at 11:11

answered Dec 28 '15 at 09:03

Erez Hod

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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: http://stackoverflow.com/questions/24024549/dispatch-once-singleton-model-in-swift. – Martin R Dec 28 '15 at 10:33
1

You should make the `default init private`. Please add this code `private init() {}` – Luca Angeletti Dec 28 '15 at 12:05

score 0 · Accepted Answer · answered Dec 28 '15 at 08:53

0

It's this simple:

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

class Helper {

}

answered Dec 28 '15 at 08:53

Marius Fanu

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This is not a Singleton Class – Luca Angeletti Dec 28 '15 at 12:03
@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`. – Marius Fanu Dec 28 '15 at 12:13
@appzYourLife , Then is it possible for you to translate my objective-c code into swift for singleton class ? Swift way is complicated to implement. – Nata Mio Dec 28 '15 at 12:42
@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](https://en.wikipedia.org/wiki/Singleton_pattern). 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. – Luca Angeletti Dec 28 '15 at 12:52
@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. – Marius Fanu Dec 28 '15 at 13:01
@MariusFanu: I see your point. But I still don't think that simply declaring a global constant referencing the instance of a class does mean implementing the Singleton Design Pattern. – Luca Angeletti Dec 28 '15 at 13:07
The annoying part is each time i need to access foo() for example i have to go throw : Helper.sharedInstance. foo() instead of just helper.foo() ? any suggestion to utilize it ?@appzYourLife – Nata Mio Dec 28 '15 at 13:14
@NataMio: look [here](http://stackoverflow.com/questions/24024549/dispatch-once-singleton-model-in-swift) at the **Class Constant** section. – Luca Angeletti Dec 28 '15 at 13:16
I have to do like : `Singleton. sharedInstance.fooexample()` which is very long each time i want to access `fooexample()`. is possible to do like `sharedInstance.fooexample()` or `Singleton.fooexample()` ? – Nata Mio Dec 28 '15 at 13:25

Get singleton instance in swift

2 Answers2