Converting objective-c block syntax to swift

Question

I've been practicing blocks a bit and would like some help converting this one from Objective C to Swift.

The below Objective C code works just fine... logging a random number every second

- (void)viewDidLoad {
[super viewDidLoad];


NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(returnNumberMethod) userInfo:nil repeats:YES];

}

 - (void)returnNumberMethod {

[self returnRandomInt:^(NSInteger randNum) {

    NSLog(@"%ld", (long)randNum);
}];

}

- (void)returnRandomInt:(void (^)(NSInteger randNum)) completion {

NSInteger number = arc4random_uniform(100);

completion(number);

}

My swift attempt, but it didn't work, I know the syntax is wrong but would someone be able to help with translating the above code? Thank you!

override func viewDidLoad() {
    super.viewDidLoad()

    let timer = NSTimer(timeInterval: 1, target: self, selector: "getRandomNumber", userInfo: nil, repeats: true)

}

//block practice

func getRandomNumber() {

    self.randomNumber { (number) -> NSInteger in

        let numberString = NSString(format: "%ld", number)

        print(numberString)
    }
}

func randomNumber(completion: (number: NSInteger) -> NSInteger) {

    let numero = arc4random_uniform(100)

}

Answer 1

You are close: make the completion callback a method accepting an UInt32 (since that is the type returned by arc4random_uniform) and return void. Additionally change the syntax you are calling the function with. The following works:

func getRandomNumber() {
    randomNumber { number in
        let numberString = NSString(format: "%ld", number)
        print(numberString)
    }
}

func randomNumber(completion: (UInt32 -> Void)) {
    let numero = arc4random_uniform(100)
    completion(numero)
}

You can make use of the string magic in swift by using print("\(number)") instead of the string format.