" Getting these two worlds to cooperate requires a lot of 'glue code' to make them work together. The 'model-view-controller' paradigm introduces the controller object in between the view (the GUI class) and the model (the object) to communicate between the other two objects . The actual implementation of the controller object can vary quite a bit, but the idea of an object to 'transform' events to changes in data and execution of methods is the essence of this pattern. What does "event driven" mean? Was there ever an application which did not respond to user events. . ? Just because an application responds to events does not mean it is "event driven". Event driven means it spends much of its time waiting for an event and then takes action if and when an event occurs. Abercrombie And Fitch Model Photo Contrast this with some programs that do not respond to events at all, but simply do their job and terminate. For example, an operating system command to display the current time. "

" The model should have no direct knowledge of the view. However, the observer pattern can be used to provide some indirection between model and view, allowing the model to notify interested parties of a change. A view object can register itself with the model and listen for changes but the model itself remains view-agnostic. The controller does not pass domain objects (the model) to the view although it might issue a command telling the view to update itself. The user interface waits for further user interactions, which begins the cycle anew. Benefits and liabilities Although widely used, MVC has both advantages and disadvantages compared to other design options, and individual circumstances should be used to choose the most appropriate design. We discuss some of those here. Abercrombie Guy Model Pic View instability vs. model stability If constructed correctly, models can enjoy a fair degree of stability (owing to the stability of the domain model), whereas user interface code usually undergoes frequent and sometimes dramatic change (typically because of usability problems, the need to support growing classes of users, or simply the need to keep the application looking "fresh"). "