What is the difference between beginTrackingWithTouch and touchesBegan?
Having just run into this today, I think the key difference is that beginTrackingWithTouch and friends are only for tracking - not anything else - in particular not for target/action handling. So if you override touchesBegan, then you'd also be responsible for calling sendActionsForControlEvents when touches ended. But if you use beginTrackingWithTouch, that's handled for free.
I discovered this by implementing beginTrackingWithTouch (for a custom button control) thinking it was just a sideways replacement for handling touchesBegan. So in endTrackingWithTouch, I called sendActionsForControlEvents if touchInside was true. The end result was that the action was called twice, because first the builtin mechanism sent the action, then I called it. In my case, I'm just interesting in customizing highlighting, so took out the call to sendActionsForControlEvents, and all is good.
Summary: use beginTrackingWithTouch when all you need to do is customize tracking, and use touchesBegan when you need to customize the target/action handling (or other low-level details) as well.
beginTrackingWithTouch:withEvent:
1) subclass UIControl
2) Sent to the control when a touch related to the given event enters the control’s bounds.
3) To provide custom tracking behavior (for example, to change the highlight appearance). To do this, use one or all of the following methods: beginTrackingWithTouch:withEvent:, continueTrackingWithTouch:withEvent:, endTrackingWithTouch:withEvent:
touchesBegan:withEvent:
1) subclass UIResponder
2) Tells the receiver when one or more fingers touch down in a view or window.
3) There are two general kinds of events: touch events and motion events. The primary event-handling methods for touches are touchesBegan:withEvent:, touchesMoved:withEvent:, touchesEnded:withEvent:, and touchesCancelled:withEvent:. The parameters of these methods associate touches with their events—especially touches that are new or have changed—and thus allow responder objects to track and handle the touches as the delivered events progress through the phases of a multi-touch sequence. Any time a finger touches the screen, is dragged on the screen, or lifts from the screen, a UIEvent object is generated. The event object contains UITouch objects for all fingers on the screen or just lifted from it.