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Timer.scheduledTimer(withTimeInterval: 1, repeats: true) { timer in
    let randomNumber = Int.random(in: 1...20)
    print("Number: \(randomNumber)")

    if randomNumber == 10 {
        timer.invalidate()
    }
}

//tener una variable NSTimer global para poder pararlo

-(void) startDotsAnimation{
    dotsSequence = 1;
    
    if (!timerDotsAnimation) {
        timerDotsAnimation = [NSTimer scheduledTimerWithTimeInterval:1
                                                              target:self
                                                            selector:@selector(animateDots)
                                                            userInfo:nil
                                                             repeats:YES];
    }
}

-(void) animateDots {
    
    switch (dotsSequence) {
        case 1:
            self.lblDots.text = @".";
            break;
            
        case 2:
            self.lblDots.text = @". .";
            break;
            
        case 3:
            self.lblDots.text = @". . .";
            dotsSequence = 0;
            break;
    }
    
    dotsSequence++;
}

-(void) stopDotsAnimation {
    if (timerDotsAnimation) {
        [timerDotsAnimation invalidate];
        timerDotsAnimation = nil;
    }
}