MVC pattern and implementation in java

Agenda Context Problem Solution What is MVC? MVC Architecture Common MVC Implementation MVC Interaction Order MVC Pattern MVC Responsibilities Advantages of MVC Implementation of MVC

CONTEXT Interactive applications with a flexible human-computer interface

PROBLEM DEFINITION User interfaces are especially prone to change requests. Different user place conflicting requirements on the user interface. Building a system with the required flexibility is expensive and error-prone if the user interface is tightly interwoven with the functional core.

PROBLEM DEFINITION The following forces influence the solution The same information is presented differently in different windows, for example, in a bar or pie chart. The display and behavior of the application must reflect data manipulations immediately. Changes to the user interface should be easy, and even possible at run-time. Support different ‘look and feel’ standards or porting the user interface should not affect code in the core of the application.

SOLUTION MVC – Model View Controller

What is MVC? MVC - Model-View-Controller - is a design pattern for the architecture of web applications. It is a widely adopted pattern, across many languages and implementation frameworks, whose purpose is to achieve a clean separation between three components of most any web application.

MVC Architecture The Model represents the structure of the data in the application, as well as application-specific operations on those data. The View renders the contents of a model. It specifies exactly how the model data should be presented. The Controller translates user actions (mouse motions, keystrokes, words spoken, etc.) and user input into application function calls on the model, and selects the appropriate View based on user preferences and Model state.

Cond… The MVC architecture divides an application (code) required to manage a user interface into three parts: Data components maintain the raw application data and application logic for the interface –model. Presentation components provide the visual representation(s) of the data --view (usually to the screen). Input-processing components handle input from the user by modifying the model--controller.

Common MVC Implementation

MVC Actions Model -- Notify view about data updates View --Change rendering as needed Controller --Select view to be rendered based on event notifications and method invocations

MVC Interaction Order User performs action, controller is notified. Controller may request changes to model. Controller may tell view to update. Model may notify view if it has been modified. View may need to query model for current data. View updates display for user. 6 View 4 Model 5 3 1 Controller 2

MVC Pattern – Model Contains application & its data Provide methods to access & update data Interface defines allowed interactions Fixed interface enable both model & GUIs to be easily pulled out and replaced Examples:- Text documents Spreadsheets Web browser Video games

MVC Pattern – View Provides visual representation of model. Multiple views can display model at same time. When model is updated, all its views are informed & given chance to update themselves.

MVC Pattern – Controller Users interact with the controller Interprets mouse movement, keystrokes, etc. Communicates those activities to the model Interaction with model indirectly causes view(s) to update

model responsibilities store data in properties implement application methods (e.g., ClockModel.setTime() or ClockModel.stop()) provide methods to register/unregister views notify views of state changes

view responsibilities create interface update interface when model changes forward input to controller controller responsibilities translate user input into changes in the model if change is purely cosmetic, update view

Advantages of MVC Separating Model from View (that is, separating data representation from presentation). More robust Easier to maintain permits run-time selection of appropriate Views based on workflow, user preferences, or Model state. Separating Controller from Model (application behavior from data representation) allows configurable mapping of user actions on the Controller to application functions on the Model.

Easy to add multiple data presentations for the same data. Multi-view applications (overview+detail, brushing,…) Different users Different UI platforms (mobile, client-side, server-side,…) Alternate designs GUI Model GUI Model GUI

Cond… Facilitates adding new types of data presentation as technology develops. Model and View components can vary independently enhancing maintainability ,extensibility, and testability. allows user interfaces (views) to be easily added, removed, or changed allows response to user input (controller) to be easily changed

COND… changes can happen dynamically at runtime promotes code reuse (e.g., one view might be used with different models) allows multiple developers to simultaneously update the interface, logic, or input of an application without affecting other source code.

Implementation of MVC

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