Changes

== Model View Controller (MVC) ==

In the days before object-oriented programming (and even for a time after object-oriented programming became popular) there was a tendency to develop applications where the code for the user interface was tied tightly to the code containing the application logic and data handling. This coupling made application code difficult to maintain and locked the application to a single user interface. If, for example, an application written for Microsoft Windows needed to be migrated to Mac OS, all the code written specifically for the Windows UI toolkits had to be ripped out from amongst the data and logic code and replaced with the Mac OS equivalent. If the application then needed to be turned into a web based solution, the process would have to be repeated again. Attempts to achieve this feat were usually found to be prohibitively expensive and ultimately ended up with the applications being completely re-written each time a new platform needed to be targeted.

== The Target-Action pattern, IBOutlets and IBActions ==

When you create an iPhone app you will typically design the user interface (the view) using the Interface Builder tool and write the view controller and model code in Objective-C using the Xcode code editor. In the previous section looked briefly at how the view controller interacts with the model. In this section we will look at how the view created in Interface Builder and our view controller code interact with each other.