Monitor for gestures from non-view-controller class - objective-c

Question

I'm wanting to monitor for up, down, left, or right swipe gestures from an external class (i.e. with the methods not in my view controller). I've managed to set this up using an external class and properties to judge which direction was pushed, but I'm now wanting to run a method inside the view controller when a swipe is detected (which will accept which direction was swiped, and act accordingly).
I'm unsure how to get a method in one class to run when a swipe is detected in another. At present, my SwipeDetector class is set up as shown below, and I'd like those kDirectionKey constants to be fed into a method in the view controller class, and for that method to fire whenever a swipe takes place. Is this something I should be using observers for? I've never used them before, seem a little daunting.
#synthesize up = _up;
#synthesize down = _down;
#synthesize left = _left;
#synthesize right = _right;
#synthesize swipedDirection = _swipedDirection;
- (void)recogniseDirectionSwipes
{
_up = [[UISwipeGestureRecognizer alloc] initWithTarget:self action:#selector(upSwipeDetected)];
_down = [[UISwipeGestureRecognizer alloc] initWithTarget:self action:#selector(downSwipeDetected)];
_left = [[UISwipeGestureRecognizer alloc] initWithTarget:self action:#selector(leftSwipeDetected)];
_right = [[UISwipeGestureRecognizer alloc] initWithTarget:self action:#selector(rightSwipeDetected)];
_up.direction = UISwipeGestureRecognizerDirectionUp;
_down.direction = UISwipeGestureRecognizerDirectionDown;
_left.direction = UISwipeGestureRecognizerDirectionLeft;
_right.direction = UISwipeGestureRecognizerDirectionRight;
}
- (void)upSwipeDetected
{
NSLog(#"Direction swipe sniffed out, and that direction was up!");
_swipedDirection = kDirectionKeyUp;
}
- (void)downSwipeDetected
{
NSLog(#"Direction swipe sniffed out, and that direction was down!");
_swipedDirection = kDirectionKeyDown;
}
- (void)leftSwipeDetected
{
NSLog(#"Direction swipe sniffed out, and that direction was left!");
_swipedDirection = kDirectionKeyLeft;
}
- (void)rightSwipeDetected
{
NSLog(#"Direction swipe sniffed out, and that direction was right!");
_swipedDirection = kDirectionKeyRight;
}
#end

Answer 1

If you're doing sophisticated gesture detection on a UIView, it would make sense to do that in the UIViewController's view. To encapsulate that functionality you would create a UIView subclass, implement your gesture handling there, then pass appropriate messages back to the controller class as needed.
The latter seems to be your main question. That's a classic case for the delegation pattern. If you opt to create a custom UIView to implement the gesture handling, let's call it FooView then you could create a formal protocol FooViewDelegate to handle messages to the view's delegate. In this case, the delegate would be your controller class. Apple docs on protocols.
Alternatively, you could just implement the gesture detection in your UIViewController subclass and no have to worry about delegation. It depends on your requirements.
As another alternative (one to which you allude), if the view controller retains a reference to the SwipeDetector class, you could observe properties on the SwipeDetector instance.
[self addObserver:self forKeyPath:#"swipeDetector.swipeDirection"
options:NSKeyValueObservingOptionNew
context:NULL];
Note that for KVO to work, you need to use the property accessors on your SwipeDetector class, e.g. self.swipeDirection = kDirectionKeyUp; instead of setting the ivars directly.