A Brief History of Controllers
It's important to remember that the MVC pattern has been around for a long time—decades before this era of modern web applications. When MVC first developed, graphical user interfaces (GUIs) were just a few years old, and the interaction patterns were still evolving. Back then, when the user pressed a key or clicked the screen, a process would “listen,” and that process was the controller. The controller was responsible for receiving that input, interpreting it and updating whatever data class was required (the model), and then notifying the user of changes or program updates (the view, which is covered in more detail in Chapter 3).
In the late 1970s and early 1980s, researchers at Xerox PARC (which, coincidentally, was where the MVC pattern was incubated) began working with the notion of the GUI, wherein users “worked” within a virtual “desktop” environment on which they could click and drag items around. From this came the idea of event-driven programming—executing program actions based on events fired by a user, such as the click of a mouse or the pressing of a key on the keypad.
Over time, as GUIs became the norm, it became clear that the MVC pattern wasn't entirely appropriate for these new systems. In such a system, the GUI components themselves handle user input. If a button was clicked, it was the button that responded to the mouse click, not a controller. The button would, in turn, notify any observers or listeners that it had been clicked. ...