Dots activity indicator

DotsActivity.m

    RACSignal* activitySignal = [[RACObserve(self, viewModel.inProgress) map:^id(NSNumber* value) {
        if (value.boolValue == NO) return [RACSignal return:@""];
        return [[RACSignal interval:0.5 onScheduler:[RACScheduler mainThreadScheduler]]
                scanWithStart:@"."
                reduce:^id(NSString* previous, id current) {
                    if (previous.length > 2) return @".";
                    return [previous stringByAppendingString:@"."];
                }];
    }] switchToLatest];