Winter 2012ACS-3913 Ron McFadyen1 Model View Controller Originated with Smalltalk development (1979) Separates a system’s classes into View, Controller, Model

Model View Controller ViewController Controller handles decisions regarding user events Model notifies its views Controller informs model to update itself according to user actions Other patterns are likely in use: Factory for creating a default controller Decorator for creating scrollable views … gets updates Winter 20122ACS-3913 Ron McFadyen

Model View Controller ViewController Strategy Model Composite Observer Winter 20123ACS-3913 Ron McFadyen

Winter 2012ACS-3913 Ron McFadyen4 Model View Controller Whenever the model’s state changes it notifies the view and the view can update itself. The model is a subject that notifies its observers (view) The controller represents a strategy for reacting to user interface events. A view has a controller, a strategy, associated with it; strategies can be swapped in and out. The controller, learning of a certain user action, may inform the model to take some action to update itself. The controller may also inform the view to take some action. The visual presentation is de- coupled from the actions required to manage user gui events. A view is typically a nested structure of components organized according to the composite pattern.

Winter 2012ACS-3913 Ron McFadyen5 Model View Controller Examples: Calculator example DJ example in text

Winter 2012ACS-3913 Ron McFadyen6 Model View Controller Calculator example (see course web pages) View: To display a log of operations To display running total and allow user to enter an operand and select an operator Model: the current state … the current total Informs the views of pertinent results Controller: Informs the model if the user selects an operator Informs views to update their display

Winter 2012ACS-3913 Ron McFadyen7 Model View Controller Assignment 5: modify this example to include a new view more operations (subtraction, division) one list of observers. Due Tuesday April 3, 2012

Winter 2012ACS-3913 Ron McFadyen8 Model View Controller DJ example in text, pages View: To display a pulsing beat (BeatBar) To display the beats per minute, and to let the user change the bpm in three ways: new value, increment, decrement Model: the current state … the current bpm Informs the views of pertinent changes Controller: Informs the model if the user changes the bpm Informs views to enable/disable buttons Note the controller interface could be described by use cases … one for each end-user goal

Winter 2012ACS-3913 Ron McFadyen9 Model View Controller MVC in practice is encountered in many variations on many platforms: e.g. these links may still be valid: Android-Developers-MVC-and-MVVM.aspx