![]() Working at the UIViewController class level also has its perks. Unlike views, view controllers don’t implement the all-important drawRect: method needed for providing custom presentations. When your application handles any kind of drawing operation in response to user touches, you need to implement touch handlers in views. By hiding the way the game pieces move in response to touches, your model code can focus on game semantics instead of view position updates.ĭrawing presents another reason to work in the UIView class. For example, you can inform your model that a pawn has moved to Queen’s Bishop 5 at the end of an interaction sequence rather than transmit a meaningless series of vector changes. Building interaction behavior directly into view classes allows you to send meaningful semantically rich feedback to your core application code while hiding implementation minutia. Further, using views for direct touch interaction may seem to contradict Model–View–Controller design orthogonality, but it can be necessary and can help promote encapsulation.Ĭonsider the case of working with multiple touch-responsive subviews such as game pieces on a board. You probably expect to separate the way an interface looks (its view) from the way it responds to touches (its controller). Handling touches in views may seem counterintuitive. Trying to implement low-level gesture control in non-responder classes has tripped up many new iOS developers. You decide where you process and respond to touches. Your application receives touches in view or view controller classes both implement touch handlers via inheritance from the UIResponder class. ![]() This depends both on how you’ve set up your application to respond (that is, whether you’ve enabled Multi-Touch interaction) and how the user touches the screen (that is, the physical number of touch points). Each UIEvent object represents a single touch event, containing single or multiple touches. The touch is passed along, from view to view, until some object takes charge and responds to that event.Īt the most basic level, touches and their information are stored in UITouch objects, which are passed as groups in UIEvent objects. When the user touches the screen, the application looks for an object to handle this interaction. As their name suggests, responders are objects that respond to events, and they act as a chain of possible managers for those events. IOS uses what is called a responder chain to decide which objects should process touches. It provides the essential components of all touch-based interaction.Įach touch conveys information: where the touch took place (both the current and previous location), what phase of the touch was used (essentially mouse down, mouse moved, mouse up in the desktop application world, corresponding to finger or touch down, moved, and up in the direct manipulation world), a tap count (for example, single-tap/double-tap), and when the touch took place (through a time stamp). Before jumping into gestures and gesture recognizers, you should gain a solid foundation in this underlying touch technology. As an iOS developer, you tell the view how to respond. ![]() It sends touch events to the view you’re interacting with. TouchesĬocoa Touch implements direct manipulation in the simplest way possible. By the time you finish reading this chapter, you’ll have read about many different ways you can implement gesture control in your own applications. You’ll also discover how to distinguish and interpret gestures, which are a high-level touch abstraction, and gesture recognizer classes, which automatically detect common interaction styles like taps, swipes, and drags. You’ll see how to create views that users can drag around the screen. This chapter introduces direct manipulation interfaces that go far beyond prebuilt controls. You can design and build applications that work directly with users’ gestures in meaningful ways. Touches are not limited to button presses and keyboard interaction. The touch represents the heart of iOS interaction it provides the core way that users communicate their intent to an application. Core iOS Developer's Cookbook, The, 5th Edition
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