Firm foundation in the main hci principles, the book provides a working

Figure 6.14 iOS UI event responder (handler) object class hierarchy. (From IOS Developers Library, 
iOS UIKit Framework Reference, 2013, https://developer.apple.com/library/ios/documentation/ 
UIKit/Reference/UIKit_Framework/_index.html [4].)

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looks for an object capable of handling the event (Figure 6.15). Because 
the hit-test view is also a responder object, an application may also take 
advantage of the responder chain when handling touch events. The 
responder chain consists of a series of next responders (each returned 
by the nextResponder method) in the sequence. The response behavior 
itself is implemented by the responder objects (i.e., the UI components 
such as the window, button, slider, etc.).
6.5 Summary
In this chapter, we reviewed three examples of UI toolkits, namely, 
those for Java3D, Android, and iOS. There are certainly many other 
UI toolkits; however, most of them are similar in their structures and 
basic underlying mechanisms. As you have seen, some UI toolkits 
include visual prototyping tools and declarative specification syn-
tax as well, which make it even more convenient for developers to 
implement user interfaces. In general, the use of UI toolkits promotes 
iOS
Events
(Touch, Motion, Remote Control, etc.)
UIKit
Event Abstraction
Event Recognition
View Object
(First responder)
View Object
(next responder)
App
App
UIEvents
UIEvents
UIEvents
UIEvents
UIResponder
Method
Raw Input
Figure 6.15 The event-processing flow and the event-driven object behavior structure. The user 
input is captured, abstracted, and recognized by the UIKit framework and queued into the proper 
application view objects (or responders), which implement the particular response behaviors using 
the UIResponder methods.

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standardization, familiarity, ease of use, fast implementation, and 
consistency for a given platform.
References
1. Oracle. 2013. Abstract Window Toolkit. http://docs.oracle.com/javase/7/
docs/api/java/awt/package-summary.html.
2. Google Developer. 2013. User interface. http://developer.android.com/
guide/topics/ui/index.html.
3. Eclipse. 2013. http://www.eclipse.org/.
4. IOS Developer Library. 2013. iOS UIKit Framework Reference. https://
developer.apple.com/library/ios/documentation/UIKit/Reference/
UIKit_Framework/_index.html.

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YS T E M
D
E V E LO P M E N T
F
R A M E W O R K
So far, we have only focused on the user interface (UI) objects and 
their behavior. Obviously, a complete application consists not only 
of UI objects, but those for the core functions of the application as 
well. How do we effectively develop the larger interactive programs 
with two such parts (i.e., UI and internal functional core)? For this, 
it is a good idea to follow an established development framework 
or methodology suited for highly interactive systems [1]. A develop-
ment framework refers to a modular approach for interactive program 
development where the core computational and interface parts are 
developed in a modularized fashion and combined in a flexible man-
ner. Such a development framework is often based on the UI toolkit, 
which provides the abstraction for the interface parts. For one, the 
framework allows the concept of plugging in different interfaces for 
the same model computation and easier maintenance of the overall 
program. In addition, such a practice also promotes the productivity 
as well as easier and less costly postmaintenance. MVC (model, view, 
and controller) is one such major framework.