Example of encapsulating a gesture recognizer's behavior within a signal's callbacks

MainViewController.m

- (void)setupDraggableHeaderGestureRecognizer {
	// setup a gesture recognizer so we can drag the "I need some daytime hours" header up and down
	@weakify(self);

	UIPanGestureRecognizer *recognizer = [[UIPanGestureRecognizer alloc] init];
	_draggableHeaderView.userInteractionEnabled = YES;
	[_draggableHeaderView addGestureRecognizer:recognizer];
	RACDisposable *disposable = [[[recognizer
		rac_gestureSignal]
		scanWithStart:RACTuplePack(@(_mapViewHeightConstraint.constant), @0)
			   reduce:^(RACTuple *translations, UIPanGestureRecognizer *gestureRecognizer) {
				   @strongify(self);
				   switch (gestureRecognizer.state) {
					   case UIGestureRecognizerStateBegan:
						   return RACTuplePack(@(self.mapViewHeightConstraint.constant), @0);

					   case UIGestureRecognizerStateChanged: {
						   CGFloat verticalTranslation = floorf([gestureRecognizer translationInView:self.mapView.superview].y);
						   CGFloat initialConstant = ((NSNumber *) translations.first).floatValue;
						   CGFloat constant = initialConstant + verticalTranslation;
						   if (constant < [self minimumMapHeight])
							   constant = [self minimumMapHeight];
						   else if ((CGRectGetMinY(self.mapView.frame)+constant) > (CGRectGetMinY(self.searchButton.frame) - CGRectGetHeight(self.draggableHeaderView.frame))) {
							   constant = CGRectGetMinY(self.searchButton.frame) - CGRectGetHeight(self.draggableHeaderView.frame) - CGRectGetMinY(self.mapView.frame);
						   }
						   return RACTuplePack(translations.first, @(constant - initialConstant));
					   }

					   case UIGestureRecognizerStateCancelled:
						   return RACTuplePack(translations.first, translations.first);

					   default:
						   return translations;
				   }
			   }]
		subscribeNext:^(RACTuple *tuple) {
			@strongify(self);
			self.mapViewHeightConstraint.constant = ((NSNumber *) tuple.first).floatValue + ((NSNumber *) tuple.second).floatValue;
		}];

	_draggableHeaderDisposable = [RACDisposable disposableWithBlock:^{
		[_draggableHeaderView removeGestureRecognizer:recognizer];
		[disposable dispose];
	}].asScopedDisposable;
}